PRINCIPLES OF FOOD PROCESSING AND PRESERVATION updated

PRINCIPLES OF FOOD PROCESSING AND PRESERVATION (Volume-1.1) by: - Mohit Jindal P a g e | 1
PRINCIPLES OF FOOD PROCESSING AND PRESERVATION
DETAILED CONTENTS
Scope and trends in food industry
Status of Indian food industry with emphasis on State of Haryana. Definition of food – food technology,
food science, food preservation and food engineering – basic considerations. Importance of food processing
and preservation. Classification of foods on the basis of shelf life, pH, origin; Different types of food
spoilage viz. microbiological, bio-chemical, chemical, physical and their effects on food quality. Principles
of food preservation.
Preservation by sugar and salt
Principles of Salt and sugar preservation, Intermediate Moisture Food (IMF) like jam, jelly and
marmalade. Techniques of pickling.
Preservation by Low Temperature
Low temperature required for different foods – refrigeration – refrigeration load, refrigeration systems; slow
and fast freezing, freezing process; types of freezer advantages and disadvantages of freezing; storage and
thawing of frozen food.
Preservation by High Temperature
Pasteurization, Sterilization, Canning: their Definition, Method, advantages and disadvantages.
Moisture Removal
Evaporation, concentration, drying and dehydration, types of dryers, advantages and disadvantages,
selection of dryers.
Food Additives including Chemical Preservatives-
Classification, functions and uses in foods
8. Preservation of foods by Radiation – Irradiation of foods, Radiation doses for spices, onions,
potatoes and meat. Concept of microwave heating effect on food quality
LIST OF PRACTICALS
Study of changes in fruits/vegetables during storage
Peeling of fruits and vegetables
Preparation of brine and syrup
Blanching of seasonal fruits and vegetables
Dehydration of fruits & vegetables
Preparation of fruit bars
Freezing of seasonal vegetables, meat and fish products

Preparation of Jam, Jelly & squash
Pickle preparation
Storage of frozen products
Preparation of sauerkraut
Visit to fruits and vegetable industry to see above operations
RECOMMENDED BOOKS
Food Science by NN Potter, CBS publishers, New Delhi
Technology of Food Preservation by Desrosier, The Avi Publishing Company, Inc., Westport
Principles of Food Science Vol. – I by Fennema, Karrel, McGraw-Hill Book
Company, New York
Preservation of Fruits and Vegetables by Girdhari Lal, Sidhapa and Tandon, CBS Publishers, Delhi
Hand book of Analysis of Fruits and Vegetables by S Ranganna, Tata Me Graw- Hill. Publishing Company,
New Delhi
Fruits and Vegetable Processing by Cruss, Oxford and IBH Publishing Co., New Delhi
Food Science by Mudambi, New Age International Pvt Ltd Publishers, New Delhi
Basic Food Preparation( Manual)
Fruit & Vegetable Processing by Bhatt, Verma, Tata Mc Graw Hill Publishing Company Limited,. New
Delhi
Commercial Vegetable Processing by Woodroof, vannostrand Reinhold, New York
Preservation of Fruits & Vegetables by IRRI, Oxford & IBH Publishing, New Delhi
Food Canning Technology by Larcousse & Brown
Food Composition & Preservation by Bhawna Sabarwal, Commonwealth Publishers 1999, New Delhi.
Food Preservation by S.K. Kulshrestha, vikas publishing house Pvt. Ltd., New Delhi
Processing Foods by Oliverra, CRC Press, New York
Principles & Practices for the Safe Processing of Foods by Heinz, H J Heinz Company, UK

Scope and trends in food industry:-Status of Indian food industry with emphasis on State of Haryana.
Definition of food – food technology, food science, food preservation and food engineering – basic
considerations. Importance of food processing and preservation. Classification of foods on the basis of
shelf life, pH, origin; Different types of food spoilage viz. microbiological, bio-chemical, chemical,
physical and their effects on food quality. Principles of food preservation.
Scope and Trends
Food preservation prevents losses and wastage of nutrients from foods and allows people to benefit from the
nutrient concentrated foods. Enormous reduction in spoilage and wastage of perishable foods builds up
country’s economy by making more food available to the people at affordable prices. It provides much
needed employment avenues to many individuals in the food processing and allied fields. With the spurt in
growth of food preservation industries, the demand for the trained personnel has substantially increased.
With the recent liberalization policy and lifting of trade restrictions, there is a vast potential of exports of the
processed foods. Multinational food giants are finding India as a promising market. In case, Indian products
can meet the international standards of quality as well as compete successfully, we can earn valuable foreign
exchange.
Availability of cheap labour, Government Subsidy for cold storage and processing units, convenience of
roads in case for marketing and transport. Availability of cans, bottles, and other equipments at cheap rate,
there is tremendous for export of processed products like Jam, jelly, marmalade, pickles, etc. dehydrated and
dried vegetables in addition to domestic demand in India. Five-year tax holiday for new food processing
units in fruits and vegetables processing along with other benefits in the budget has bolstered the
government’s resolution of encouraging growth in this sector.
India is the second-largest producer, next to China, of fruit and vegetables in the world, contributing a total
of 150 million tonnes of the produce to the global production annually. But only 2.2% of the fruit and
vegetable are processed here as compared to countries like USA (65%), Philippines (78%) and China (23%).
That’s why there is a huge opportunity for companies looking at investing in this sector in the country.
Although India is a very large producer of fruits, but yield levels of most of the fruits are relatively low as
compared to those in other major fruit producing countries. India is a front runner in many fruits and
vegetables with share in world production (Indian Horticulture Database 2013) as follows:
44.1% of mango
42.6% Papaya
25.6% of banana
20.2% of onion
35.6% of cauliflower
About 25 to 30 per cent of the total production is lost due to spoilage at various post-harvest stages. In value
terms, the post harvest wastage and losses per year are estimated at over Rs. 3000 crores. Because of these
losses, the per capita availability of fruits is only of the order of 75 gm per person per day, which is just half
of the requirements of a balanced diet. This happens due to:
Lack of Transport
Lack of Storage facilities
Poor availability of package materials
Poor road conditions
Lack of local cold storage to store the surplus
This results in the inadequate pricing of produce during off season and spoilage. This provides the farmer to
gain a higher price on his product, due to palatability of the product.
The major fruits grown are banana, mango, citrus, guava, grapes, apple and pineapple which constituted
nearly 80 per cent of the total fruit production in the country. Banana has the largest share of 31.7 per cent in

total fruit production, followed by mango with 28 per cent. Production of mango has remained almost
stagnant during the decade 1983-93. The annual growth in production during 1983-93 was 9.6 per cent in
the case of banana, 10.3 per cent for papaya, 9.4 per cent for grapes and 4.7 per cent in respect of citrus
fruits. The major fruit producing states are Andhra Pradesh, Maharashtra, Karnataka, Bihar, Uttar Pradesh,
Tamil Nadu, Kerala and Gujarat. These eight states contribute 78 per cent of the total fruit production.
The Indian gourmet food market is currently valued at US$ 1.3 billion and is growing at of 20 per cent. It is
expected to cross US$ 2.8 billion by 2015 and is expected to reach US$ 78 billion by 2018. Share of online
food ordering would be in single digits of the overall food ordering business which in 2014 was estimated to
be around Rs 5,000-6,000 crore (US$ 800.19-960.12 million). We are growing at 20-30 per cent month-on-
month.
The total food production in India is likely to double in the next 10 years with the country’s domestic food
market estimated to reach US$ 258 billion by 2015.
Consumption pattern
Out of the total production of fruits and vegetables, nearly 76 per cent is consumed in fresh form, while
wastage is around 20 to 22 per cent. Only 2 per cent of vegetable production and 4 per cent of fruit
production are being processed.
Processing facilities
It is significant to note that the current installed capacity can process only 3 to 4 per cent of their total
production of fruits and vegetables in the country. There were around 4100 to 4200 processing units licensed
with an installed capacity of 12 lakhs tonnes. The actual production in 1993 was only 5.6 lakhs tones
implying a capacity utilization of less than 50per cent. Being seasonal in nature, the units operate for less
than 150 days in a year.
Exports
The government has initiated several policy measures for encouraging exports of processed fruits and
vegetables. As a result, exports of these products have increased from Rs. 122.5 crores in 1990/91 to Rs.
332.4 crores in 1993/94.
India’s share in word exports of fresh and processed fruits and vegetables was quite insignificant being just
1 per cent. India’s major exports are in fruit pulp, pickles, chutneys, canned fruits and vegetables,
concentrated pulps and juices, dehydrated vegetables and frozen fruits and vegetables.
India has the potential to achieve a 3% share in the world trade of agricultural and food products by 2015.
The vast production base offers India tremendous opportunities for export. During 2013-14, India exported
fruits and vegetables worth Rs. 8760.96 crores which comprised of fruits worth Rs. 3298.03 crores and
vegetables worth Rs. 5462.93 crores.
Demand
The demand for processed fruits and vegetables comes from both the domestic and export markets. In the
domestic market, a substantial share is contributed by defence, hotels and restaurants. Household consumption
accounts for less than 50 per cent of the production. India’s exported are constrained by several factors such as
poor quality, lack of standardization and unattractive packaging.

Importance and need of Food Processing and Preservation
Food preservation activities are as old as human race. It had an important role in the spread of civilization.
Delay in the consumption or processing of fresh foods alters its freshness, colour, texture, palatability and
nutritive value, organoleptic desirability, aesthetic appeal and safety. To make food available throughout the
year, humans have developed methods to prolong their storage life i.e. to preserve them. The rotting process
can be postponed by adding preservatives, optimizing storage conditions, or applying modern techniques.
Therefore, preservation of foods is imperative in order to increase their shelf life. Food preservation can result
in several advantages, some of which are substantial. These include:
• increased shelf-life
• decreased hazards from microbial pathogen
• decreased spoilage (microbial, enzymatic)
• inactivation of anti-nutritional factors
• ensured round the year availability of seasonal foods
• perishable foods that can be transported to far-off distances from the site of production
• increased availability of convenience foods (e.g. Ready-to-serve beverages, Instant mixes etc.)
• increased variety of foods, some with enhanced sensory properties and nutritional attributes.
Preservation in some cases produces a different form of the products which are of great importance in various
cuisines. E.g. raisins, squash and wines made from grapes.
Need for Food Preservation
When food is available more than its present use/ consumption, it should be preserved for future
utilization. Thus, preservation activities ensure proper utilization of food. Preservation of fresh produce is
needed for following reasons:
• For increasing availability of certain foods which have a short growing season such as fruits and
vegetables, for use throughout the year.
• For utilization of surplus crops and prevent wastage.
• For saving money by preserving foods when they are most plentiful, cheaper and are of good
quality.
• For producing food which is easier to store, distribute and transport and that can be made available
in all places at all times.
• For meeting the needs of the people for food in secluded and difficult areas.
• For ensuring supply of protective foods in homes, hotels and other such places.
Aim of food preservation is to prevent undesirable changes in the wholesomeness, nutritive value or
sensory quality of food and reduce chemical, physical and physiological changes of an objectionable
nature and eliminate contamination.
The goal of food preservation is to increase the shelf life of a food while keeping it safe. It ultimately
ensures its supply during times of scarcity and natural drought. The main objectives of food preservation
include lengthening lag phase of bacteria growth; delaying undesired autolysis; minimizing pest/ physical
damage and preventing microbial action.

CLASSIFICATION OF FOOD ONTHE BASIS OF SHELF LIFE
Foods can be categorized into three main groups on the basis of their shelf life or perish ability.
• Non-perishable or stable foods: These foods do not spoil unless they are handled carelessly. They
should be stored in a cool, dry place. They can be stored for one year. They should be picked and
cleaned before storage. If necessary, grains can be washed with water to remove any dust and dirt
sticking to them. These should then be dried in the sun, allowed to cool and stored in containers with
tight fitting lids.
Non-perishable foods include sugar, jaggery, hydrogenated fat, vegetable oil, ghee, whole
grains, dais, whole nuts, dry salted fish and meat, papads, canned foods, preserves such as pickles,
jams and murabbas.
• Semi-perishable foods: These foods do not spoil for a fairly long time if stored properly. They are
more stable due to microbiological contamination and natural chemical breakdown as compare to
other perishable foods.
Foods in this group can be stored for a week to a couple of months at room temperature without
the development of any undesirable changes in flavour and texture.
Semi perishable foods include processed cereals, pulses and their products like flour, Bengal
gram flour, millet flour, semolina, parched rice, popcorn, etc. Their shelf life depends on the storage
temperature and moisture in the air.
Other semi perishable foods are potatoes, onions, nuts, frozen foods kept solidly frozen at "zero"
to -18°C and canned foods that need refrigeration, apples, citrus fruits, pumpkin, etc.
• Perishable foods: This is the largest of the three groups and includes most of the food items we
consume every day, such as milk and milk products, eggs, poultry, meat, fish, most fruits and
vegetables such as bananas, pineapple, papaya, green leafy vegetables, etc.
Because of contain high amounts of protein, moisture and other nutrients; they are an ideal
medium for bacterial growth. They also spoil easily by natural enzymatic changes. They have a very
short shelf life of a few hours to a few days, after which they spoil rapidly. Food of this group may
be responsible for the food-borne illnesses.
CLASSIFICATION OF FOODS ACCORDING TO pH
Most foods are derived either from plants or from animals. pH of food is important because low acid
food with a high pH (4.6 and above) are prone to contamination by clostridium botulism, which produce a
toxin. Hence it is necessary to inactive this organism in such food.
• Low acid foods
The foods having pH above 5.3 are called low acid foods. For example: peas, corn, lima beans etc.
• Medium acid foods
The foods which have pH between 4.3 and 5.3 are called medium acid foods. For example:
asparagus, beets, pumpkin, spinach etc.
• Acid foods

Foods which have pH between 3.7 and 4.5 are called acid foods. For example: pears, pineapple,
tomatoes etc.
• High acid foods
Foods having pH 3.7 or lower are included in this category. For example: Berries and sauerkraut.
CLASSIFICATION OF FOODS ON THE BASIS OF ORIGIN:-
• Plant origin
• Animal origin
1. Plant origin:-
I. Cereals and grasses- cereals are members of grass family grown for their grain and most
important plants eaten by men. Example-wheat, rice, corn, sorghum etc. principle source of
carbohydrate although they contain protein, fats some vitamin and minerals also. Cereals
contain a good amount of thiamin and niacin.
II. Legumes- they are second to the cereals as important source of human food. They are the
meat of vegetable world and are closed to animal flesh in protein food value. Soya bean is
one of the oldest known food plants. The seed is richest in food value of all the vegetables
consumed throughout the world. Example:- soya bean, Bengal gram, lenticels, mong dal etc.
III. Nuts: - A nut is a seed one ceiled fruit with a hard shell. Example-hazels nuts, chest nuts,
peanut, coconut etc.
They are of three types following as:-
a) High protein content. Almond
b) High carbohydrates content. Chest nuts
c) High fat content. Coconut, cashew nuts, wall nut.
IV. Fruit and tuber-Plant roots and modified root are storage organ for plant and also are
important for us.-carrot, beats, radish, turnips, and sweet potato.
V. Vegetables-They provide variety of taste and texture. Example- all vegetables
VI. Fruit- they are ripened ovaries of a flowers addible portion is usually the fleshing covering
over the seeds.- fruit vegetables-pumpkin, cucumber, tomato are technical fruit but eaten as
vegetables.
VII. Sugar and other carbohydrates food:- the carbohydrates food commonly used are cane sugar,
jiggery, glucose, honey, syrup, custard powder etc. they serve mainly as a source of energy
VIII. Condiments and spices- they are important source of nutrient in average diet but are used
mainly for enhancing the palability of diet. The flavour and acceptability of food preparation
2. Animal origin
Meat, fish, milk and milk products, animal by products, liver
Factors Affecting food Spoilage
The types of spoilage of a particular food item depend to a great extent on the following:
 The composition of food:
The composition of food influences its susceptibility to spoilage. For example- presence of proteins
and carbohydrates especially sugars are preferred by microorganisms for energy source. Very few
utilize fat for energy production.
 Structure of the food item:
Whole healthy tissues of food from inside are sterile or low in microbial content. Skin, rind or shell
on food works as its protective covering from spoilage microorganisms.
 Types of microorganisms involved:
The types of microorganisms present in food depend on its composition of food.

 Conditions of storage of the food:
Conditions of storage of food affect the growth of microorganisms. Even if the proper storage of
food is done, the food loses its freshness and nutritive value if it is stored for too long
Different types of food spoilage viz. microbiological, bio-chemical, chemical, and
physical and their effects on food quality.
• Spoilage Due to Chemical Reactions-Chemical reactions takes place in the presence of atmospheric
oxygen and sunlight. Two major chemical changes, which occur during the processing and storage of
fruits and vegetables, are lipid oxidation and non-enzymatic browning which deteriorate sensory
quality, colour and flavour.
Lipid oxidation is influenced by light, oxygen, high temperature and the presence of iron and
copper, and water activity.
Non-enzymatic browning is one of the major causes of deterioration which takes place during
frying, cooking, storage of dried and concentrated foods through Maillard, caramelization and
ascorbic acid oxidation.
Maillard reaction occurs due to reactions between reducing sugars and amino acids in the presence
of heat and results in formation of black brown insoluble pigments.
Caramelization of sugars occurs in presence of high heat and low moisture content in the food.
Oxidation of fatty acids to other chemicals like aldehydes, ketones, alcohols and esters also results
in off-flavours
• Spoilage due to bio-chemical- Different biochemical reactions in foods and plants tissues are
catalyzed by enzymes. Enzymes are complex chemical substances, which are present in all living
organisms and tissues, which control essential metabolic processes. Enzymatic spoilage is the
greatest cause of food deterioration. They are responsible for certain undesirable or desirable changes
in fruits, vegetables and other foods. Examples involving endogenous enzymes include:
 the post-harvest senescence and spoilage of fruit and vegetables;
 Oxidation of phenols in plant tissues to orthoquinones by phenolases, peroxidases and polyphenol
oxidases (PPO). These orthoquinones rapidly polymerize to form brown pigments known as melanin
leading to enzymic browning;
 sugar – starch conversion in plant tissues by amylases;
 Post-harvest demethylation of pectic substances in plant tissues (leading to softening of plant tissues
during ripening, and firming of plant tissues during processing).
If enzymatic reactions are uncontrolled, the off-odors, and off-colours may develop in foods.
Enzymes can act between 0°C and 60°C but 37°C is optimum temperature. Enzymes can be
permanently inactivated by heat. It has been seen that for each 10°C rise in temperature, the activity
of microorganisms and enzymes increases by at least twice, in the range 0-60°C. Above this, heat
quickly destroys enzymes and stops living cells from working. All enzymes are inactivated at 80°C.
Decreased temperatures therefore work by slowing down these changes
• Spoilage Due to Physical Factor-Physical factors such as temperature, moisture and pressure can
also cause food spoilage. Physico-chemical reactions are caused by freezing, burning, drying and
bruising of fruits and vegetables during storage, handling and transportation, which result in food
deteriorations.

Food processing or storage causes some deterioration in colour of fruits and vegetables due to
the degradation of the chlorophyll resulting dull olive-brown colour. Dehydrated green peas and
beans packed in glass containers undergo photo-oxidation and loss of desirable colour occurs.
Freezer induced damage observed in frozen foods affects its quality. Anthocyanins, the pigment in
fresh and processed foods, form complexes with metals resulting in the change in colour. E.g. Red
sour cherries react with tin and form undesirable purple complex. Carotenoid, another colour
pigment, degrades by oxidation in the presence oxygen, light and heat.
• Factors Affecting Growth of Microorganism- (Spoilage Due to Insects, Pests and Rodent) Growth
of microbes and their propagation in the food are one of the important factors to food spoilage. They
decrease the nutritive value and wholesomeness of food. The main categories of foods subject to
insects and pest attack are fruits, vegetables, grains and their processed products.
Warm humid environment promote insect growth, although most insects will not breed if the
temperature exceeds above 35°C or falls below 10°C. Many insects cannot reproduce satisfactorily
unless the moisture content of their food is greater than 11 per cent. The presence of insects and pests
and their excreta in foods may render consumable loss in the nutritional quality, production of off-
flavours.
The products of insect and pests activities such as webbing, clumped-together food particles
and holes can also reduce the food values. Rats and mice carry disease-producing microorganisms on
their feet and/or in their feces and urine and contaminate the food by their presence.
Effects of Spoilage on Nutritional Quality
Effect of spoilage on nutrient degradation cannot be generalized because of the diverse nature of the
various nutrients as well as the chemical heterogeneity within each class of compounds and the complex
interactions of the above variables. Foods contaminated with microorganisms may cause food borne illness.
Food borne illnesses can be classified as food infection and food intoxication. Food infection occurs due to
growth of pathogenic microorganisms in victim’s digestive tract causing diarrhea, vomiting, fever etc. For
example- Salmonellosis due to consumption of Salmonella sp. contaminated food. The major nutritional
changes which occur in foods due to microbiological, enzymatic and chemical reactions are listed in below
Table.
Type of change Nutritional quality related changes in food
Microbiological Growth or presence of toxicogenic and/or infective microorganisms
Enzymatic 1. Hydrolytic reactions catalyzed by lipases, proteases, etc.
2. Lipoxygenase activity
Chemical 1. Oxidative rancidity
2. Non-enzymatic browning
3. Nutrient losses
Food intoxication or poisoning is caused due to ingestion of food containing toxic compounds
produced by pathogenic microorganisms in food. E.g. Staphylococcus aureus and Clostridium botulinum
causes food poisoning. Measures for the prevention of food spoilage: Manipulation of factors controlling the
conditions required for microbial growth and enzyme action viz. temperature, moisture, air and pH other
than the food itself can help prevent food spoilage
Principles of Food Preservation
All food preservation methods are based upon the general principle of preventing or retarding the causes

of spoilage caused by microbial decomposition, enzymatic and non-enzymatic reaction, chemical or
oxidative reactions and damage from mechanical causes, insects and rodents etc. Food preservation
operates according to three principles, namely:
1. Prevention or delay of microbial decomposition
by keeping out microorganisms (asepsis)-
Prevention or delay of microbial decomposition brought out by
1. Keeping out microorganisms or asepsis- Nature provides protective coverings around the food in the
form of shells of nuts, die skins of fruits and vegetables, the shells of eggs, and the skin or fat on
meat or fish. These protective coverings act as a preservative factor, thereby preventing or delaying
microbial decomposition. Even in the food industry several aseptic methods are adopted to prevent
the contamination of foods during its processing. Like canning. Packaging of foods is also an
application of asepsis.
2. Removal of microorganisms’ e.g. washing, filtration etc.
3. Hindering the growth and activity of microorganisms by controlling the conditions required for the
growth and activity of microorganisms by use of low temperature, drying, maintenance of anaerobic
conditions or chemicals
4. Killing microorganisms by heat or irradiation
Prevention or delay of self-decomposition of foods by
1. Destroying or inactivating food enzymes e.g. blanching, low temperature storage, chemical
preservation, drying etc.
2. Preventing or delay of chemical reactions e.g. prevention of oxidation with the use of antioxidants as
oxygen speeds up decomposition of food and antioxidants deprives food from oxygen.
Prevention of damage because of external factors such as insects, rodents, dust, odour, fumes, and
mechanical, fire, heat or water damage. Eg.
To retain the natural taste and aroma of a product, it is necessary to preserve it soon after preparation,
without allowing it to stand for any length of time. Various methods of preservation are employed and each
has its own merits. Items of food can be damaged either by insects and animals or by mishandling. The
entire operation of preserving foods is divided into three stages of careful handling:
Proper packaging
Quick and effective transportation
Providing good storage facilities, like silos for grains and cold storages for fruits and vegetables
About
Early scientific research into food technology concentrated on food preservation. Nicolas Appert’s
development in 1810 of the canning process was a decisive event. The process wasn’t called canning then
and Appert did not really know the principle on which his process worked, but canning has had a major
impact on food preservation techniques.
Louis Pasteur's research on the spoilage of wine and his description of how to avoid spoilage in 1864 was an
early attempt to apply scientific knowledge to food handling. Besides research into wine spoilage, Pasteur
researched the production of alcohol, vinegar, wines and beer, and the souring of milk. He developed
pasteurization—the process of heating milk and milk products to destroy food spoilage and disease-
producing organisms. In his research into food technology, Pasteur became the pioneer into bacteriology and
of modern preventive medicine.
• Food Technology is a branch of food science that deals with the production processes that make
foods. Early scientific research into food technology concentrated on food preservation.

• Food science The study of the basic chemical, physical, biochemical, and biophysical properties of
foods and their constituents, and of changes that these may undergo during handling, preservation,
processing, storage, distribution, and preparation for consumption
• Food engineering is a multidisciplinary field of applied physical sciences which combines science,
microbiology, and engineering education for food and related industries.
• Food preservation is the process of treating and handling food to stop or slow down food spoilage,
loss of quality, edibility, or nutritional value and thus allow for longer food storage. Microorganisms.
Principles of Salt and sugar preservation, Intermediate Moisture Food (IMF) like jam, jelly and
marmalade. Techniques of pickling.
Preservation by salt
Salt at a concentration of 15 to 25 per cent is sufficient to preserve most products. It inhibits enzymatic
browning (interfere with the action of proteolytic enzymes) and discoloration and also acts as a antioxidant.
Salts also cause food dehydration by drawing out water from the tissue cells. Salt in the form of brine is used
for canning and pickling of vegetables which contain very little sugar and hence sufficient lactic acid cannot
be formed by fermentation to act as preservative. It exerts its preservative action by
• Causing high osmotic pressure resulting in the plasmolysis of microbial cell.
• Dehydrating food as well as microorganisms by drawing out and tying up the moisture by ion
hydration.
• Ionizing to yield the chloride ion which is harmful to microorganisms.
• Reducing the solubility of oxygen in water, sensitizing the cells against carbon dioxide, and
interfering with the action of proteolytic enzymes.
Salt is employed to control microbial population in foods such as butter, cheese, cabbage, olives, cucumbers,
meat, fish and bread.
Preservation by Sugar
Syrups containing 66 per cent or more of sugar do not ferment. Sugar absorbs most of the available water
with the result that there is very little water for the growth of microorganisms hence their multiplication is
inhibited, and even those already present die out gradually. . Dry sugar does not ferment. Thus sugar acts as
a preservative by osmosis. The high osmotic pressure of sugar creates conditions that are un-favorable for
the growth and reproduction of most species of bacteria, yeasts and moulds. The preservative action of
moderate strength of sugar can be improved if invertase is used to increase the concentration of glucose
relative to sucrose Fruit syrup, jam, jelly, marmalade, preserve, candy, crystallized fruit and glazed fruit are
preserved by sugar.
INTERMEDIATE-MOISTURE FOODS (IMF)
Adjustment and control of water activity to preserve semi moist foods has attracted increasing attention.
Intermediate-moisture foods or semi moist foods, in one form or another, have been important items of diet
for a very long time. Generally, they contain moderate levels of moisture, of the order of 20- 50% by weight,
which is less than is normally present in natural fruits and 'vegetables, but more than is left in conventionally
dehydrated products. In addition, 'intermediate-moisture foods contain sufficient dissolved solutes to
decrease water activity below that required to support microbial growth. As a consequence, intermediate-
moisture foods do not require refrigeration to prevent microbial deterioration. There are various kinds of
intermediate-moisture foods: natural products such as honey; manufactured confectionery products high in
sugar, jellies, jams, and bakery items such as fruit cakes; and partially dried products including figs, dates
etc. In all of these products, preservation is partially from high osmotic pressure associated with the high
concentration of solutes; in some, additional preservative effect is contributed by salt, acid, and other
specific solutes.
FRUIT JAM

Jam: Jam is prepared by boiling whole fruit pulp with cane sugar (sucrose) to a moderately thick
consistency with out retaining the shape of the fruit. As per FPO specification 45 parts of fruit to each 55
parts of sugar and contain 0.5-0.6% acid and invert sugar should not be more than 40%. is used for
preparation of jam.
Or
Jam is a product with reasonably thick consistency, firm enough to hold the fruit tissues in position,
and is made by boiling fruit pulp with sufficient sugar.
Preparation of Jam
Jam can be prepared from one kind of fruit or from two or more kinds. It may be made from
practically all varieties of fruit. Apple, papaya, carrot, strawberry, mango, grapes, pineapple, etc. are used
for the preparation of jams. Various combinations of different varieties of fruit can be often made to
advantage, pineapple being one of the best for blending purposes because of its pronounced flavour and
acidity.
Selection of fruit: Fruit should be in right proportion which gives good quantity of pectin and also natural
flavour. For this fully ripped and ripped fruit are used in right proportion.
Preparation of fruit pulp: Sound fruit is sorted, washed in running water or, preferably, brush-washed and
prepared. The mode of preparation varies with the nature of the fruit. For example, mangoes are peeled,
steamed and pulped; apples are peeled, cored, sliced, heated with water and pulped; plums are scalded and
pulped; peaches are peeled and pulped; apricots are halved, steamed and pulped; berries are heated with
water and pulped or cooked as such.
Addition of sugar: To make jams and jellies, up to a maximum of 25% of corn syrup for sweetness can be
utilized. Generally, cane sugar of good quality is used in the preparation of jams. The proportion of sugar to
fruit varies with type and variety of fruit, its stage of ripeness and acidity. A fruit pulp to sugar ratio of 1:1 is
generally followed. This ratio is usually suited to fruits viz., berries, currants, plums, apricots, pineapple and
other tart fruits.
Addition of acid: Citric, malic or tartaric acids are present naturally in different fruits. These acids are also
added to supplement the acidity of the fruits deficient in natural acids during jam making. Addition of acid
becomes necessary as adequate proportion of sugar- pectin- acid is required to give good set to the jam. The
recommended pH for the mixture of fruit juice and pectin is 3.1. The acidity of finished jam varies between
0.5 to 0.7 % depending on the type of the jam. It is often advisable to add acid at the end of cooking which
leads to more inversion of sugar. When acid is added in the beginning, it will result in poor set.
Processing/boiling: Fruit pulp is cooked with the requisite quantities of sugar and pectin, and finished to
69% Total Soluble Solids (TSS). Permitted food colours, requisite amount of citric acid and flavourings are
added at this stage. The boiling process, in addition to excess water removal, also partially inverts the sugar,
develops the flavour and texture. During jam boiling, all microorganisms are destroyed within the product.
When this is filled hot into clean receptacles which are subsequently sealed, and then inverted the hot jam
contacts the lid surface, thus prevents the spoilage by micro-organisms during storage.
Judging of End Point
Concentration of jam is finished at an optimum point avoiding over cooking which leads to
economic losses due to less yield. But under cooking will result in the spoilage of jam during storage
due to fermentation. The finishing or end point of jam can be determined by the following methods.
Drop test: This method is the simplest way and commonly used by
housewives where no other facilities are available. In this method, a little
quantity of jam is taken from the boiling pan in a tea spoon and allowed to
air cool before putting a drop of it in a glass filled with water. Settling
down of the drop without disintegration denotes the end point
By sheet test: In this test, a small portion of jam is taken with a large
spoon or wooden ladle, cooled slightly and then allow to drop off
keeping the spoon or ladle in horizontally inclined position. If the

jam drops like syrup, further concentration is needed. If it is in the form of flake or forms a sheet, the
finishing point is attained
Refractometer method: This is the most common
method used by small and large scale fruit processing
industries for jam making. The cooking is stopped when
the refractometer shows 69o
Brix.
Boiling point method: Jam containing 69% TSS boils
at 106 oC at sea level. This method is simplest and best to determine the finishing point of jam.
By weighing method: Weighing method is more laborious and time consuming. Here the boiling pan is
weighed before and again after transferring the extract and sugar in to it. The end point is attained when the
net jam weight is one and a half times of the quantity of sugar added.
Packaging The product is packed in cans or glass jars, and cooled, followed by labeling and packaging.
Containers including can or jar gets sterilized when hot jam (not less than 85oC) is poured in them. Boiling
the containers in hot water can also effect sterilization.
Special Care/ Problems in Jam Production
Crystallization: The final product should contain 30–40% invert sugar. If the percentage is less than 30,
cane sugar may crystallize out on storage and if it is more than 50 the jam will become a honey-like mass
due to high inversion of 40 % sugar into glucose. Corn syrup or glucose may be added along with cane sugar
to avoid crystallization.
Sticky or gummy jam: Because of high percentage of total soluble solids, jams tend to become gummy or
sticky. This problem can be solved by addition of pectin or citric acid, or both.
Premature setting: This is due to low total soluble solids and high pectin content in the jam and can be
prevented by adding more sugar. If this cannot be done a small quantity of sodium bicarbonate is added to
reduce the acidity and thus prevent pre-coagulation.
Surface graining and shrinkage: This is caused by evaporation of moisture during storage of jam. Storing
in a cool place can reduce it.
Microbial spoilage: The mould attack on jam can be eliminated by storing them at less than 90% RH
(Preferably at 80% RH). It is also advisable to add 40 ppm sulphur dioxide in the form of KMS. In the case
of cans, sulphur dioxide should not be added to the jam as it causes blackening of the internal surface of the
can.

FRUIT JEELY
Jelly: Jellies are gellified products obtained by boiling fruit juices with sugar, with or without the addition of
pectin and food acids.
OR
Jelly is a semi solid product prepared by boiling a clear, strained solution of pectin containing fruit extract,
free from pulp, after addition of sugar and acid.
A jelly is a semisolid product prepared by boiling fruit with water, expressing as water (pectin) extract),
adding sugar, and concentrating to such consistency that gelatinization takes place on cooling. A perfect
jelly should be transparent, well set, but not too stiff, and should have the original flavour of the fruit. It
should be of attractive colour and keep its shape when removed from the mould. It should not be gummy,
sticky, or syrupy or have crystallized sugar.
Preparation of Jelly
A. Selection of fruits: Guava, sour apple, plum, papaya, certain varieties of banana and gooseberry are
generally used for preparation of jelly. Other fruits can also be used but only after addition of pectin
powder, since these fruits are low in pectin content. Fruits can be divided into four groups according
to their pectin contents. This classification is highly useful in preparation of jelly, because pectin is
the important component, which is responsible for the texture of the jelly. The classification is as
follows.
• Rich in pectin and acid: sour apple, grape, lemon, sour oranges, jamun, sour plum.
• Rich in pectin but low in acid: apple, unripe banana, pear, ripe guava, etc.
• Low in pectin but rich in acid: sour apricot, sweet cherry, sour peach, pineapple and strawberry.
• Low in pectin and acid: ripe apricot, peach, pomegranate, strawberry and other over ripe fruits.
B. Extraction of pectin/boiling: After selection, the fruits are washed thoroughly. Most of the fruits are
boiled for extraction of the juice in order to obtain maximum yield of juice and pectin. Boiling
converts protopectin into pectin and softens fruit tissues. Very juicy fruits do not require the addition
of water and are crushed and heated to boiling only for 5 min. Firm fruits are cut or crushed and

boiled with water for 5 min. The length of boiling will vary according to the type and texture of fruit.
The amount of water added to the fruit must be sufficient to give a high yield of pectin e.g. apples
require one half to an equal volume of water, where as citrus fruits require 2-3 volumes of water for
each volume of sliced fruits.
C. Straining and clarification: Pectin extract is obtained by straining the boiled fruit mass through bags
made of linen, flannel, or cheese cloth folded several times. For large scale production, the fruit
extract is made to pass through filter presses for clarity.
• Analysis of extract: Clarified extract is analyzed for pH, acidity, soluble solids and pectin content by
common laboratory methods.
For determining pectin content the easiest way adopted is precipitating the pectin with
alcohol. A rapid test for evaluation of juice pectin content is by mixing a small sample of juice with
an equal volume of 96% alcohol in a tube. The mixture from the tube is then emptied on a plate. The
appearance of a compact gelatinous precipitate indicates sufficient pectin content for jellification
(Figure J-1). Insufficient pectin will remain in numerous small granular lumps
.
Figure J-1 .4: Pectin test for jelly extract. a) Low pectin extract; b) High pectin extract
D. Addition of sugar and pectin: Based on the pectin test of the fruit extract, quantity of sugar to be
added is worked out. For the extract rich in pectin, sugar equal to the quantity of the extract is added.
To the extract with moderate pectin 650 – 750 g of sugar should be added to each kg of extract. For
juices rich in pectin, jellification will occur without pectin addition. If pectin content is less, 1-2%
powder pectin will be added to the juice.
E. Addition of acid: Jelly strength increases with increasing hydrogen ion concentration until an
optimum pH is reached which are generally 3.2 at 65%sugar concentration. Jellying strength depends
on the quantity of pectin and the acid present in the original fruit extract.
F. Processing/boiling: The juice is boiled up to remove about half of the water that has to be
evaporated. Then the calculated sugar quantity is added gradually. The remainder of the water is
evaporated until a TSS (refractometric extract) of 65% is reached. During boiling it is necessary to
remove foam / scum formed. Product acidity must be brought to about 1% (malic acid)
corresponding to pH > 3. Any acid addition is performed always at the end of boiling. Boiling of
jellies is performed in small batches (25-75 kg) in order to avoid excessively long boiling time which
brings about pectin degradation.
G. Judging of End Point: Boiling of jelly should not be prolonged, because excessive boiling results in
greater inversion of sugar and destruction of pectin. The end point can be judged by sheet test, drop
test, refractometry, thermometer, and by weighing the boiling mass. Methods like sheet test, drop
test, and weighing of the boiling mass can be done in the similar way as in the case of jam
preparation.
• Refractometer method: This is the most common method used in fruit processing industries for jelly
making. The cooking is stopped when the refractometer shows 65o
Brix.
• Temperature test: A solution containing 65% TSS boils at 105o
C. Heating of the jelly to this
temperature would automatically bring the concentration of solids to 65%. Endpoint of finishing jelly
should be 4.5-5o
C higher than that of the boiling point of water at that place.
H. Packaging: After jelly is ready, it is skimmed to remove foam. It is cooled slightly before pouring
into dry and hot glass jars. Cooling is optional and is carried out up to 85oC, in double wall baths
with water circulation. Filling is performed at a temperature not below 85oC in receptacles (glass
jars, etc.), which must be maintained still for about 24 hours to allow cooling and product
jellification.

Problems in Jelly Making
The most important difficulties that are experienced are as follows:
•Failure to set: This may be due to the addition of too much sugar, lack of acid or pectin, cooking below/
beyond the end-point.
•Colour changes: Darkening at the top of the jars can be caused by storing them in too warm place or by an
imperfect jar seal.
•Gummy jelly: It is the result of prolonged or over cooking in which more than desired inversion of sugar
occurs
•Stiff jelly: Over cooking or using too much pectin makes too tough jelly which fails to spread when applied
on bread.
•Cloudy or foggy jellies: It is due to the use of non-clarified juice or extract, use of immature fruits, over-
cooking, over-cooling, non-removal of scum, faulty pouring, and premature gelation.
•Formation of crystals: It is due to addition of excess sugar and also due to the over-concentration of jelly.
This excess sugar comes from over cooking, too little acid or from under cooking.
•Syneresis or weeping of jelly: The phenomenon of exudation of fluid from a gel is called syneresis or
weeping and is caused by several factors. The factors include; excess of acid, too low concentration of sugar,
insufficient pectin, premature gelation, and fermentation
•Presence of mold: Due to imperfect sealing and insufficient sugar.
•Colour fading: This is due to high temperature and bright light in storage room. Another possible cause
could be the insufficient processing to destroy the enzymes affecting colour or the elevated processing
temperature, which might cause colour fading. Trapped air bubbles can also contribute to the chemical
changes by oxidation.

FLOW DIAGRAM FOR JELLY MAKING
MARMALADE
Marmalade is a fruit jelly in which slices of the fruit or its peel are suspended.
OR
Marmalade is a clear jelly in which shreds of peel are suspended. It is generally prepared from citrus fruits
Marmalade preparation is similar to jelly with the difference that it contains citrus fruits like oranges and
lemons in which shredded peel is used as the suspended material. In the preparation of marmalade bitterness
is regarded as desirable characteristic of product. The principles of jelly making, apply also to the reparation
of marmalade Marmalades are classified into two:
Jelly marmalade
Jam marmalade
Jelly Marmalade
Good quality jelly marmalade can be prepared from a combination of Sweet orange/ Mandarin
orange and sour orange in a 2:1 proportion. Shreds of sweet orange (Malta) peel are used in the preparation.

Selection of fruit
Sound, ripened fruit is sorted, washed, and prepared. The mode of preparation varies with the nature
of the fruit. The fruits are then cut in to slices and are boiled for the preparation of extract.
Extraction of pectin/boiling: After selection, the fruits are washed thoroughly. Most of the fruits are boiled
for extraction of the juice in order to obtain maximum yield of juice and pectin. Boiling converts protopectin
into pectin and softens fruit tissues. The amount of water added to the fruit must be sufficient to give a high
yield of pectin e.g. apples require one half to an equal volume of water, where as citrus fruits require 2-3
volumes of water for each volume of sliced fruits.
Straining and clarification: Pectin extract is obtained by straining the boiled fruit mass through bags made
of linen, flannel, or cheese cloth folded several times. For large scale production, the fruit extract is made to
pass through filter presses for clarity
Analysis of extract: As like Jelly.
Preparation of peel shreds: The outer layer of yellow portion of citrus fruits is peeled off carefully. The
stripped-off peel is cut into slices of about 2-2.5 cm long and 1-1.2 mm thick. Boiling in water with 0.25%
sodium bicarbonate or 0.1% ammonia solution can soften the shreds. Before addition to the jelly, the shreds
may be kept in heavy syrup for some time to increase their bulk density to avoid floating on the surface
when it is mixed with jelly.
Addition of sugar and pectin: Based on the pectin test of the fruit extract, quantity of sugar to be added is
worked out. For the extract rich in pectin, sugar equal to the quantity of the extract is added. To the extract
with moderate pectin 650 – 750 g of sugar should be added to each kg of extract. For juices rich in pectin,
jellification will occur without pectin addition. If pectin content is less, 1-2% powder pectin will be added to
the juice.
Addition of acid: Jelly strength increases with increasing hydrogen ion concentration until an optimum pH
is reached which is generally 3.2 at 65%sugar concentration. Jellying strength depends on the quantity of
pectin and the acid present in the original fruit extract.
Processing: During boiling, the impurities in the form of scum are occasionally removed. When the
temperature of the mixture reaches 103oC, the prepared shreds of peel are mixed in it at the rate of 5-7% of
the original extract. Boiling is continued till the end point is reached. The end point is judged in the same
way as in the case of jelly. Like jelly, marmalade also contains 65% TSS at 105oC. Boiling should not
prolong for more than 20 min, after the addition of sugar to get bright and sparkling marmalade.
Cooling: The marmalade is cooled to permit the absorption of sugar by the shreds from the surrounding
syrup. If the marmalade is filled in hot, the shreds may come to the surface instead of remaining in
suspension. During cooling, the product is gently stirred occasionally for uniform distribution of shreds.
When marmalade temperature reaches around 85oC, viscosity of syrup increases and a thin film begins to
form on surface, which prevents shreds from coming to surface.
Flavouring: This is done by adding some flavour or orange oil to the product near the end of boiling to
supplement the flavour lost during boiling. Generally, a few drops of orange oil are mixed in marmalade
before filling into containers.
Packaging and Storage: Like jams and jellies, marmalade is also filled into jars and cans at a temperature
around 850C. Storage of marmalade must be done in dry rooms (relative humidity at about 75%), well
ventilated, medium cool places (temperature 10-20oC), disinfected and away from direct sunlight and heat.
These measures are necessary because marmalade is a hydroscopic product and, by water absorption,
favorable conditions for mould development are created.
Jam Marmalade
Jam marmalade is practically made by the method used for preparation of jelly marmalade except that the
pectin extract is not clarified. The orange peel after removing albedo portion is sliced into 0.3 cm thick
pieces and treated in the same way as recommended for jelly marmalade. The sliced fruit of orange, lemon,
or grape fruit after removing peel is mixed with little quantity of water and boiled to soften. The boiled
mixture is pressed through coarse pulper to remove seed and to get thick pulp. The pulp is mixed with equal
quantity of sugar and cooked to a consistency of 65o
Brix or consistency of jam. The treated shreds are mixed
in the jam when it is slightly cool. Some orange oil is also mixed in the marmalade before filling into

containers. Filling and packaging is done in the similar way as adopted for packaging of jelly and jelly
marmalade.
Problems in Marmalade Making- Browning during storage is very common which can be prevented
by the addition of 0.09g of potassium metabisulphite (KMS) per kg of marmalade and not using tin
containers. KMS dissolved in a small quantity of water is added to the marmalade while it is cooling. KMS
also eliminates the possibility of spoilage due to moulds.
PICKLES
Pickle is an edible product preserved in a solution of common salt and vinegar. It is one of the most
ancient method of preserving fruits and vegetables. Pickles are good appetizers and add to the palatability of
meal. They stimulate the flow of gastric juice and thus help in digestion. Several kinds of pickles are sold in
Indian market. Mango pickle ranks first. Pickles can also be prepared from fruits and vegetables like lemon,
amla, onion, cauliflower, cabbage, beans, cucumber, bitter gourd, jackfruit, turnip etc.Fruits are generally
preserved in sweetened and spiced vinegar, while vegetables in salt.
Pickling Process
The preservation of food in common salt or in vinegar is called pickling. Pickling may also be the
result of fermentation by lactic acid forming bacteria, which are naturally present in large numbers on the
surface of fresh vegetables and fruits. These bacteria can grow in acid medium and in the presence of 8-
10% salt solution, whereas the growth of majority of undesirable organisms is inhibited. Lactic acid bacteria
are most active at 30oC, so this temperature should be maintained, as far as possible, in the process of
pickling. Pickling is done in two stages.
Stage I can be done by any of the three following methods:
i) Fermentation with dry salting,
ii) Fermentation in brine, or
iii) Salting without fermentation.
Stage II is finishing and packing.
Fermentation with Dry Salting
In this method, the vegetable is treated with dry salt. The salt extracts the juice from the vegetables and
forms the brine, which is fermented by lactic acid bacteria. The method of dry salting in general is as
follows:
The vegetable is washed, drained, weighed for preparing pickles.
Several alternate layers of the prepared vegetable and salt (20-30 g of dry salt/ kg vegetables) are kept in a
vessel which is covered with a cloth and a wooden board and allowed to stand for 24 hrs. During this period
brine is formed by osmosis. As soon as the brine is formed, the fermentation process starts and the CO2
begins to evolve.
When fermentation is over, gas formation stops. Under favorable conditions fermentation is completed in 8-
10 days, however in cold weather it may take 2 to 4 weeks. When sufficient lactic acid has been formed,
lactic acid bacteria stop to grow and no further change takes place in vegetables.
Precaution should be taken against spoilage by aerobic microbes, because in the presence of air “pickles
scum”, a kind of wild yeast, is formed which brings about putrefaction and destroys the lactic acid.
The product may be preserved and kept by excluding air.
Fermentation in Brine
In this method steeping of the vegetables in brine, it penetrates in the tissues of the vegetables and
soluble material present in vegetable diffuses into the brine by osmosis. The soluble material includes
fermentable sugars and minerals. The sugars serve as food for lactic acid bacteria, which convert them into
lactic and other acids. The acid brine thus formed acts upon vegetable tissues to produce characteristic taste
and aroma of pickle. The amount of brine required is usually half the volume of vegetables. Brining is the
most important step in pickling. The growth of the majority of spoilage organisms is inhibited by brine

containing 15% salt. Lactic acid bacteria are salt-tolerant and can grow in brine of 8-10% strength. In brine
containing 10% salt, fermentation precedes somewhat slowly so 5 % brine used for fair fermentation.
Fermentation takes place to some extent up to 15 % but stops at 20% brine strength. After fermentation
process, the salt content is now increased gradually, so that by the time pickle is ready, salt concentration
reaches 15%.
Salting Without Fermentation
In this type of process vegetables are washed, prepared and is mixed with salt (250 g/kg of prepared
material). This high salt concentration will inhibit the fermentation. After curing of Vegetables with large
amount of salt they are drained and excess of salt is removed by soaking them in cold or warm water.
Thereafter, the vegetables are stored in plain vinegar of 10% strength for several weeks. Vegetables can also
be stored in sweetened and spiced vinegar. The spices can be added in the ground form or essential oil of
spices may be added to impart the spice flavour.
VARIOUS PICKLES
At present, pickles are prepared with salt, vinegar, oil or with a combination of above ingredients with
spices. These methods are discussed below:
Preservation with Salt
Salt improves the taste and flavour and hardens the tissue of vegetables and controls fermentation. Salt
content of 15% or above prevents microbial spoilage. This method of preservation is generally used only for
vegetables, which contains very little sugar. Since the sugar content is less, sufficient lactic acid cannot be
formed by fermentation to act as preservative. However, some fruits viz., mango, lemon, etc. are also
preserved with salt. An example for pickle preparation with salt is shown
Mangoes (Matured green)
↓
Washing
↓
Peeling
↓
Slicing
↓
Putting slices in jar
↓
Sprinkling salt
↓
Putting in sun for one week
(Shaking jar at least twice a day to mix the salt)
↓
Mixing spices
↓
Storage at ambient temperature (In cool dry place)
Flow chart of mango pickle
Preservation with Vinegar
This technology is based on the addition of food grade vinegar which has a bacteriostatic action in
concentrations up to 4% acetic acid and bactericidal action in higher concentrations. Vegetables preserved in
vinegar need to reach a final concentration of 2-3% acetic acid in order to assure their preservation.

To achieve this final concentration, 6-9% acetic acid vinegar is used, as related to the specific ratio of
vinegar: vegetable. This higher concentration treatment helps to expel the gases present in the intercellular
spaces of vegetable tissue.
In vinegar pickles, salt (2-3%) and sometimes sugar (2-5%) are also added. If the vinegar
concentration is lower than 2%, vinegar pickles need to be submitted to pasteurization in order to assure
their preservation. Mango, garlic, chilies, etc. are preserved as such in vinegar. Vinegar pickles are the most
important pickles consumed in other countries.
Onion (small)
↓
Peeling
↓
Blanching for 5 minutes
↓
Filling blanched onions in jar
↓
Addition of salt
↓
Keeping for 1-2 days
↓
Draining off water
↓
Addition of vinegar and Spices
↓
Storage
Flow chart of onion pickle
Preservation with Oil
Oil pickles are highly popular in India. They are highly spiced. In India, mustard oil, rapeseed oil, sesame oil
are generally used. The fruits or vegetables should be completely immersed in the edible oil. Cauliflower,
lime, mango and turnip pickles are the most important oil pickles. The pickle remains in good condition for
one to two years if handled properly. A schematic flow chart of lemon pickle by using oil as preservative is
shown in
Lemon
↓
Washing
↓
Cutting into 4 pieces
↓
Squeezing out juice from 1/4th amount of fruit
↓
Mixing spices and salt with juice
↓
Mixing with pieces
↓
Filling in jar
↓
Keeping in sun for 4-6 days
↓
Addition of oil after heating
↓

Cooling it
↓
Storage
Flow chart of lemon pickle
Preservation with Salt, Vinegar, Oil and Spices
This method combines the advantages of fermentation action of salt and the preservation action of both
vinegar and oil. The flavouring property of spices is also made use of. The spices are usually fried in oil and
mixed to the prepared fruit/ vegetable before the addition of vinegar. The spices can be added separately or
in the form of spice vinegar. A schematic flow chart of tomato pickle by using salt, vinegar, oil and spices as
preservative is shown
Tomatoes
↓
Washing
↓
Blanching for 5 minutes
↓
Cooling immediately in water
↓
Peeling & Cutting into 4-6pieces
↓
Frying all ingredients in a little oil (except vinegar)
↓
Mixing with pieces
↓
Heating for 2 minutes & Cooling
↓
Addition of vinegar & remaining oil
↓
Filling in jars & storage
Flow chart of tomato pickle

Preservation by Low Temperature- Low temperature required for different foods – refrigeration –
refrigeration load, refrigeration systems; slow and fast freezing, freezing process; types of freezer
advantages and disadvantages of freezing; storage and thawing of frozen food.
The freezing process consists of pre-freezing operations, freezing, and frozen storage. Depending on
the food being frozen, some pre-freezing steps are: washing, husking, shelling, cutting, boning, trimming,
pitting, and slicing. Inspection and grading on long moving belts, formerly a visual operation, is now being
increasingly mechanized.
Fruits may have sugar or syrup added, and vegetables may be subjected to steam or hot water
blanching to retard enzymatic or chemical changes such as browning and off-flavor development that can
occur during subsequent storage. Filling and sealing of packages are usually done by complicated machines
designed for the purpose.
FREEZING TECHNOLOGY
Basically there are three methods of preservation. Their main aim is to control the activities of
microorganisms. In short you can also refer to them as 3K’s.They are
1) Keep them away
2) Kill them
3) Keep them away from growing
The Freezing technology is based on the third principle of preservation which is Keep them away
from growing. Temperature of the product to –10°C to –20°C Low temperature retards the biochemical
reactions occurring in foods and prevents biochemical reactions in food. Microorganisms also get
inactivated at low temperature. But the formation of ice crystals within the structure of most food products
creates changes in the structure and gives negative changes in the quality characteristics of the product.
Freeze food required continuous maintaining the low temperature not only during process but also
during storage and distribution.
THE FREEZING POINT OF FOODS

Living cells contain much water, often two-thirds of more of their weight. In this medium there are
organic and inorganic substances, including salts and sugars and acids in aqueous solutions, and more
complex organic molecules, such as proteins which are colloidal suspension. Thus more the salt, sugar,
minerals and proteins in a solution the lower its freezing point (depression of freezing point) and the longer
it will take to freeze when put in freezing chamber. If water and fruit juice for example are placed in a
freezer, the water will freeze first.
The freezing time depends upon number of factors such as dimensions, shape of product,
thermal properties, and temperature of refrigerant medium.
Frozen foods have great advantage is microorganisms do not grow in foods when the temperature is –10°C
or colder. Generally freezing preserves taste, texture and nutritional value of foods better than any other
preservation method.
The common terms are Cool Storage, Refrigeration and Freezing. Let us see what the difference
between each other is.
Difference between cool storage, refrigeration and freezing
Temperature
Cool storage 16 to –2°C Microorganism Spoilage microorganism can grow rapidly at
temp.>10°C. Some grow below 0°C if water is unfrozen.
Refrigeration 4.5-7°C Pathogenic microorganisms grow slowly. Psychotropic
Microorganisms grew
Freezing -2°C to lower No significant growth of spoilage or pathogenic m/o.
However, multiplication of microorganisms can take
place if food is thawed.
Freezer storage –18°C -----do---
QUICK AND SLOW FREEZING
During freezing process the product temperature is lowered and most water is transferred into ice
crystals. With decreasing temperature the liquid phase becomes more and more concentrated.
• Quick freezing is defined as the process where the temperature of the food passes through the zone
of ice crystal formation in 10 minutes or less. The process removes quick removal of water and small
ice crystals are formed in it. Rapid freezing technique, sometimes called cryogenic freezing, has
reduced freezing times. Rapid freezing rates result in better texture retention after thawing for many
products. Because of the higher cost of cryogenic freezing, this method is usually limited to high-
cost items where improved quality or yield more than pays for increased cost.
• Whereas slow freezing involves slow removal of water
and process may take 3-72 hours. This also involves ice
crystal formation which has more damaging effect on
the texture.
The advantages of quick freezing over slow freezing are
that:
• smaller ice crystal are formed hence there is less
mechanical destruction of intact cells of the food;
• there is shorter period of solidification and therefore
less time for diffusion of soluble materials and for
separation of ice;
• there is more prompt prevention of microbial growth;
• there is more rapid slowing down of enzyme action.
• Quick frozen foods therefore are supposed to thaw to a
condition more like that of the original food than slow-
frozen foods

Freezing Process of Water
The material to be frozen first cools down to the temperature at which nucleation starts. Before ice can form,
a nucleus, or a seed, is required upon which the crystal can grow; the process of producing this seed is
defined as nucleation. Once the first crystal appears in the solution, a phase change occurs from liquid to
solid with further crystal growth. Therefore, nucleation serves as the initial process of freezing, and can be
considered as the critical step that results in a complete phase change. During freezing of water, the water
molecules arrange themselves in a tetrahedral fashion. These results in a hexagonal crystal lattice which is
loosely built and has relatively large hallow spaces resulting in high specific volume. This is the reason for
increase in volume of water on freezing. You must have observed ice cubes floating on water. The density of
ice at 0° C is only 0.9168. Water can exist in three phases, viz., solid, liquid and gas.
Freezing
At temperature below the freezing point of water (−18 to −400C), growth of microorganisms and
enzyme activity are reduced to minimum. Most perishable foods can be preserved for several months if the
temperature is brought down quickly and the food is kept at these temperatures. Foods can be quickly frozen
in about 90 minutes or less.
Quick frozen foods maintain their quality and freshness when they are thawed because only very small ice
crystals are formed when foods are frozen in this manner. Frozen foods should, always be kept at
temperatures, below −5 0
C. Properly frozen (–12 to –17 0
C by excluding air), juice retains its freshness,
colour and aroma for a long time.
Refrigeration Load:-
A product refrigeration laud is the quantity of heat that must be removed to reduce the temperature of
the product from its initial; temperature to the temperature consistent with good frozen food storage. Cooling
load on the cooling system determines the size of the refrigeration, and, consequently, its energy
consumption. (This does not affect the COP or efficiency: without cooling load will not be a COP or
effectiveness.)
Less load, the lower the power consumption. Load, as a rule, consists of many different components. You
may be able to reduce or eliminate one or more of them. Application storage (e.g. cold store or retail
Cabinet) load includes:

• transmission load, which is heat transferred into the refrigerated space through its surface;
• product load, which is heat removed from and produced by products brought into and kept in the
refrigerated space;
• internal load, which is heat produced by internal sources (e.g., lights, electric motors, and people
working in the space);
• infiltration air load, which is heat gain associated with air entering the refrigerated space;
• equipment-related load
Refrigeration Load
When computing refrigeration load, the most conservative approach is to calculate each part at its expected
peak value. The combined result can overstate the actual total load by as much as 20 to 50%. Perhaps the
heat loads of goods which are at a higher temperature than the temperature of storage. You pay for some of
these heat gains in two times. For example, you pay for engine start evaporator fan, but you also pay for the
cooling system to heat it puts at cooled space. Processing of applications, the majority of the heat loads, as a
rule, from the product, chilled or frozen, although there may be stranger heat gains. More information about
reducing these heat loads are given in the GPG 279 Cut employment costs for refrigeration.
Freezing Systems
The freezing process can be accomplished using
either indirect or direct contact systems. Most
often, the type of system used will depend on
the product characteristics, before and after
freezing is completed.
Indirect Contact Systems
In numerous food products freezing systems the
product and the refrigerant are separated by a
barrier throughout the freezing process. This is called an indirect contact system. Although many systems
use a non- permeable barrier between product and refrigerant, indirect freezing systems include any system
without direct contact, including those where the package material becomes the barrier. These include plate
freezer, air blast freezer and freezer for liquid foods.
Direct Contact Systems
Direct contact freezing systems operate with direct
contact between the refrigerant and the product. In
most situations these systems operate more efficiently
since there is no barrier to heat transfer between the
refrigerant and the product. All direct contact freezing
systems are designed to achieve rapid freezing, and
the term individual quick freezing (IQF) applies.
IQF generally refers to freezing of solid
food/pieces/grains like green peas, cut beans, cauliflower pieces, meat, fish etc. While quick freezing relates
mostly to liquid, pulpy or semi liquid products like fruit juices, mango/papaya concentrates and purees etc.
There is no clumping together of pieces or grains.
They remain individual separate pieces. Individual quick freezing have advantages:
•Smaller ice crystals are formed; hence, there is less mechanical destruction of intact cells of the food.

•More rapid prevention of microbial growth.
•More rapid slowing down of enzymatic action.
Disadvantages
Brine is a good refrigerating medium but it cannot be used for fruits.
It is very difficult to maintain the medium at a definite concentration and also to keep it free from dirt and
contamination.
This includes fluidized bed freezing, immersion freezing and cryogenic freezing.
Direct Contact Systems Freezers:-
Fluidized-Bed Freezer
When the air velocity
is increased to the point
where it exceeds the velocity
of free-fall of the particle,
fluidization occurs; this is
called fluidized-bed freezing.
Fluidized bed freezer system
operate with direct contact
between refrigerant and the
product and are used to freeze
particulate foods such as peas, cut corn, diced carrots, and strawberries. Fluidized bed freezing is a
modification of air-blast freezing. Solid food particles ranging in size from peas to strawberries can be
fluidized by forming a bed of particles 1-5 in. Particulate foods are fed by a shaker onto a porous trough.
The food is pre-chilled and high velocity refrigerated air fluidizes the product, freezes it and moves it in
continuous flow for collection and packaging. An air velocity of at least 375 lineal ft/min is necessary to
fluidize suitable particles, and an air temperature of about –34°C is common. freezing time varies with
conditions, some representative times for various products are listed in Table 1.
Product Time to reduce temperature from 21°C to –18 °C, min
Peas 3-4
Diced carrots 6
Cut green beans 5-12
Strawberries 9-13
French fried potatoes 8-12
Fish fillets 30
Best results are obtained with Fluidized bed freezing the products that are small and uniform in size (e.g.,
peas, limas, cut green beans, strawberries, whole kernel corn, brussel sprouts).
The advantages of fluidized bed freezing as compared to conventional air-blast freezing are:
• More efficient heat transfer and more rapid rates of freezing
• Less product dehydration and less frequent defrosting of equipment
• Short freezing time is apparently responsible for the small loss of moisture.
A major disadvantage of fluidized bed freezing is that large or non- uniform products cannot be fluidized at
reasonable air velocities
Immersion Freezing

The immersion freezer consists of a tank with a cooled freezing media, such as glycol, glycerol, sodium
chloride, calcium chloride, and mixtures of salt
and sugar. The product is immersed in this
solution or sprayed while being conveyed through
the freezer, resulting in fast temperature reduction
through direct heat exchange. Direct immersion
of a product into a liquid refrigerant is the most
rapid way of freezing. The solute used in the
freezing system should be safe without taste,
odour, colour, or flavour, and for successful
freezing, products should be greater in density
than the solution.
Immersion freezing systems have been commonly
used for shell freezing of large particles due to the
reducing ability of product dehydration when the
outer layer is frozen quickly. A commonly seen problem in these freezing systems is the dilution of solution
with the product, which can change the concentration and process parameters. It has the following
advantages:
1. There is intimate contact between the food or package and the refrigerant; therefore, resistance to heat
transfer is minimized.
2. Although loose food pieces can be frozen individually by immersion freezing and air freezing, immersion
freezing minimizes their contact with air during freezing, which can be desirable for foods sensitive to
oxidation. For direct immersion freezing, the refrigerant used must have the following properties:
1. It should be Non-toxic.
2. It should be Clean.
3. Free from frozen tastes, odour/bleaching agents.
Cryogenic freezing Cryogenic freezing is a type of freezing which requires extremely low temperatures,
generally below -238 Fahrenheit (-150 Celsius) through direct contact with liquefied gases such as nitrogen
or carbon dioxide. This type of system differs from other freezing systems since it is not connected to a
refrigeration plant; the refrigerants used are liquefied in large industrial installations and shipped to the food-
freezing factory in pressure vessels. The refrigerants used at present in cryogenicfreezing are liquid nitrogen
and liquid carbon dioxide. In the former case, freezing may be achieved by (i) immersion in the liquid, (ii)
spraying of liquid, or (iii) circulation of its vapor over the product to be frozen. Low initial investment and
rather high operating costs are typical for cryogenic freezers. Liquid nitrogen (LN) is used in many
cryogenic freezers. The product is placed on a conveyor belt and moved into the insulated chamber, where it
is cooled.
Liquid Nitrogen freezers-Liquid nitrogen, with a boiling temperature of -196 °C at atmospheric pressure, is
a by-product of oxygen
manufacture. The
refrigerant is sprayed into
the freezer and
evaporates both on
leaving the spray
nozzles and on contact with
the products. The system
is designed in a way that
the refrigerant passes in
counter current to the
movement of the
products on the belt giving
high transfer

efficiency. Typical food products used in this system are fish fillets, seafood, fruits, and berries. Advantages
of LN freezing are as follows:
Dehydration loss from the product is usually much less than 1%
Oxygen is excluded during freezing
Individually frozen pieces of product undergo minimal freezing damage
The equipment is simple, suitable for continuous flow operations, adaptable to various production rates and
product sizes, of relatively low initial cost, and capable of high production rates in a minimal space.
The only disadvantage of LN freezing is high operating cost, and this is attributable nearly entirely to the
cost of LN.
Liquid carbon dioxide freezers-Liquid carbon dioxide exists as either a solid or gas when stored at
atmospheric pressure. When the gas is released to the atmosphere at -70 °C, half of the gas becomes dry-ice
snow and the other half stays in the form of vapor. This unusual property of liquid carbon dioxide is used in
a variety of freezing systems, one of which is a pre-freezing treatment before the product is exposed to
nitrogen spray
Indirect Contact Systems
Plate Freezers: The most common type of contact freezer is the plate freezer. In this case, the
product is pressed between hallow metal plates, either horizontally or vertically, with a refrigerant
circulating inside the plates. Pressure is applied
for good contact as schematically. In some cases,
plate systems may use single plates in contact
with the product. This type of freezing system is
only limited to regular-shaped materials or blocks
like beef patties or block-shaped packaged
products. As would be expected, these systems
are less efficient, and they are costly to acquire
and operate.
Plate-freezing systems can be operated as a batch
or continuous system.
Air or still freezing: - Air freezing is the oldest of the freezing methods. The equipment is the
simplest. The food is simply placed in an insulated cold room at a temperature maintained in the range of –
15 °C to –29°C. This method is different from the air-blast freezing, which employs air velocities. Although
there is some air movement by natural convection, in some cases gentle air movement is promoted by
placing circulating fans in the room. This method is also referred as still air freezing or sharp freezing. It is
similar to the freezing conditions that exist in home freezers except that temperatures are low i.e. –18 to –
30°C.
Air-Blast freezing: An improved version of the still air freezer is the forced air freezer, which
consists of air circulation by convection inside the freezing room. Air blast freezing is the process of taking
a product at a temperature (usually chilled but sometimes at ambient temperature) and freezing it rapidly,
between 12 and 48 h, to its desired storage temperature which varies from product to product (e.g. fish =
−20 °C, beef = −18 °C). These freezers operate at temperatures of –30 to –45°C, with forced air velocities of
10-15 m/sec. Food is frozen as batch to tunnels through which carts or belts may be moved continuously.
Particulate unpackaged foods, such as loose vegetables are fed onto the moving belt when speed is
adjustable according to the required freezing time. In other designs, food moves on trays, in a vertical
direction. Trays of particulate products such as peas or beans automatically move upward through a cold air
blast.

This freezing process allows the formation of small crystals of ice inside the cell of the product, in order to
avoid cellular damage. The air flow is normally counter-current.
There are four important points to consider in efficient operation of air blast freezing:
1. Air temperature of the freezer should be -10°F (-23°C) or preferably lower. Typically, the temperature is
-30 to -40°F (-34 to -40°C).
2. Air velocity should be 1,000-2,000 ft/min (305-610 m/min) or higher.
3. Product should not be transferred to the still-air storage room until the product has attained 0°F (- 18°C).
4. A stacking arrangement on pallets should be used that enables cold air to contact all cases.
Scrapped-surface heat exchanger-The food contact areas of a scraped – surface cylinder are
fabricated from stainless steel, pure nickel, and hard chromium plated nickel, or other corrosion resistant
material. The inside rotor contains blades that are covered with plastic laminate or molded plastic. The rotor
speed varies between 150 and 500 rpm. The cylinder containing the product and the rotor is enclosed in an
outside jacket. The cooling medium is supplied
to the outside jacket. Commonly used media
include brine or a refrigerant such as Freon. The
scraped-surface heat exchanger ensures efficient
heat exchange between the slurry and the cold
surface. Freezing systems for liquid foods can be
batch or continuous. In the case of ice-cream
freezing, the system is designed with facility for
injection of air into the frozen slurry to achieve
the desired product consistency. In a continuous
freezing system for liquid foods, the basic
system is a scraped -surface heat exchanger
using refrigerant during phase change as the
cooling medium. The rotor acts as a mixing
device, and the scraper blades enhance heat
transfer at the heat-exchange surface.
ADVANTAGES OF FROZEN FRUITS AND VEGETABLES
The fresh vegetables and fruits closely resemble their frozen counterparts in freshness, since the metabolic
activities are arrested to such an extent that all the enzymes are inactivated and microorganisms are under
control.
The taste, flavour and colour of fruits and vegetables are preserved to a maximum.
They have high nutritive value since the retention of nutrients is maximum.
Since frozen vegetables have already been subjected to a heat treatment they require less time for cooking
thus saves considerable time in kitchen and also saves fuel.
Greater convenience in handling and preparation.

Freezing is a suitable choice for preserving fruit juices containing anthocyanin and carotenoid pigments
since the retention of pigments is maximum.
They offer more hygienic food
Cent percent edible portion of food of food in each package
Since the degradative effect of heat treatment is bypassed in this, the method of freezing can retain the
pigment of such fruit juices and concentrates in its best form
Freezing can also serve as an intermittent technology for preserving commodities in bulk and supplying in a
different form when demand arises eg peas can be frozen in bulk quantities and during demand defrosted put
in a brine solution packed in flexible pouches and circulated in market whenever required.
Value for money especially off-season
No pollution problem in consuming areas
The waste collected during freezing can be utilized for production of value added products.
Limitations
1. Some water soluble nutrients may be lost during freezing as the process involves blanching in boiling
water.
2. Users of quick frozen foods need to invest on freezers to maintain the quality of the product till used. This
adds to the cost of the product.
3. Proper freezing transport facilities have to be developed for each product.
4. Quick freezing can be handled at the industrial level because it involves specialized freezing equipment,
technological know-how, strict quality control which would not be feasible on a small scale.
5. Sales markets have to be established in all markets with refrigerated display cabinets.
QUALITY AND PHYSICAL CHANGES IN FROZEN FOODS
When the food is frozen it undergoes number of quality and physical changes. Lets us see what they are.
Concentration Effects
Damage due to concentration results in
1. Gritty, sandy texture of food due to precipitation of solutes out of solution.
2. Salting out at proteins effect due to solutes remaining in concentrated solution.
3. Drop in pH drop causing proteins to coagulate.
Ice Formation
There are 2 types of fluids viz., Extra-cellular fluid (EF) and Intracellular fluid (IF). The concentration of
salts and other soluble products is higher within the cells than outside. When the product is frozen, the first
ice-crystals are formed outside the cells. The cells lose water by diffusion through the membrane. As the
cells lose water, the remaining solution within the cell becomes more concentrated and their volumes shrink
causing the cell wall to collapse.
The large ice-crystals formed outside the cell wall occupy a larger volume than the corresponding
amount of water and therefore, will execute a physical pressure on the cell wall. When the pressure becomes
high, it can damage the cell wall and lead to release of intracellular fluid (Drip loss). If the freezing rate is
high, ice-crystals are formed outside the cells. Only at very high freezing rates, small crystals are formed
uniformly throughout the tissue, both externally and internally with regard to the cells.
Freeze burn
It refers to a defect which develops during frozen storage. Moisture loss due to sublimation from surface
leads to discoloration in form of patches of light coloured tissues. This can be controlled by humidification
or lowering of storage temperature or better packaging.
Freeze Cracking

Generally, light freezing rates lead to small ice crystals and to better quality food systems. However, some
products may crack when submitted to high freezing rates as in cryogenic fluids. This is particularly seen in
mango slices frozen by liquid nitrogen. Pre-cooling prevents freeze cracking.
Moisture Loss
Moisture loss, or ice crystals evaporating from the surface area of a product, produces freezer burn. We have
already discussed what freezer burn is. This surface freeze-dried area is very likely to develop off flavours.
Packaging in heavyweight, moisture-proof packaging material will prevent freezer burn.
Drip Loss
Formation of ice crystals causes a physical pressure on the cell wall. When the pressure becomes high, it can
damage the cell wall and lead to release of intracellular fluid. This is called drip loss.
Rancid Flavour
In frozen products chemical changes can take place due to this development of rancid oxidative flavours
may develop in frozen product. This problem can be controlled by using a wrapping material which does not
permit air to pass into the product. It is also advisable to remove as much air as possible from the freezer bag
or container to reduce the amount of air in contact with the product.
PACKAGING AND STORAGE
A wide variety of materials have been used for packaging of frozen foods including plastics, metals
and paperboards. Polyethylene (PE), low density Polyethylene (LDPE) and High density Polyethylene
(HDPE) are commonly used for packaging of IQF foods i.e. fruits, vegetables and fish. Materials are easy to
seal and can be easily printed. LDPE is also easily available and cheap. HDPE can tolerate temperature in
excess to 100°C. Both HDPE and LDPE however provide relatively poor barrier protection from oxygen.
Polyester tetra phthalate (PET) is another common material used. The trays of the material are suitable for
reheating in conventional and microwave oven with stability at temperature in excess of 250°C. However
the materials are expensive and can become brittle at freezer temperature. Polystyrene (PS) is also general
plastic material used for frozen food applications. Commercial storage of frozen storage of frozen products
is usually done in deep freezers at –18 to –20°C.
STORAGE AND TRANSPORTATION OF FROZEN PRODUCE
To preserve quality and safety in frozen foods, strict temperature requirements are must during
storage, handling, distribution, and retail display and consumer storage. It is recommended that food
temperatures are maintained at –18°C or colder, although exceptions for brief periods are allowed during
transportation or local distribution when –15°C is permitted. Also, retail display cabinets should be at –
18°C, to an extent consistent with good storage practice, but not warmer than–12°C. The transport and
distribution sections of the chill chain are particularly important to control in order to ensure both safety and
quality. It is important to check temperature of foods at each point within the chill chain from storage and
transportation.
Factors Determining Freezing Rate
Food Composition- Like metals and other materials, food constituents have different thermal conductivity
properties which change with temperature. The greater the conductivity, the greater the cooling and freezing
rate. It should also be noted that fat has a much lower thermal conductivity than water, and air has a thermal
conductivity far less than that of water or fat. That why the food rich in fat will freeze in more time as
compare to food which contain less fat.
Food thickness:- the freezing point of food also depends upon the thickness of food items. When the food
items are thick there freezing time is more. But when the food item are thin there freezing time is low.
Air velocity: - if the velocity of air circulated to freeze the stored food is more faster the freezing of food
items.

Packaging: -the packaging of the food increases the freezing of the food items. Further the thickness of the
packaging material also affected the freezing time. If the packaging material is thick then freezing time will
be more and if the packing material is thin the freezing time will be less.
Contact between food and cooling medium:- if the contact between the food and cooling medium is more
than freezing time will be less because more heat will transfer from food to cooling medium due to greater
area of contact between food and cooling medium.
KEY WORDS
Freezing point: Temperature at which the liquid congeals into the solid state at a given pressure and
temperature.
Refrigerated storage: Refers to storage temperatures above freezing point of water i.e. about 16 to –2°C.
Quick freezing: Quick freezing is defined as the process where the temperature of the food passes through
the zone of ice crystal formation in 10 minutes or less. The process removes quick removal of water and
small ice crystals are formed in the process.
Slow freezing: Slow freezing involves slow removal of water and process may take 3-72 hours.
Fluidized bed freezing: A method of freezing used for particulate items such as peas, diced carrots, corn
and berries. The freezer employs a bed with a perforated bottom through which refrigerated air is blown
vertically upwards.
Blanching: Blanching is a common heat pre-treatment commonly used before processing most vegetables.
The main aim is to inactivate enzymes responsible for deterioration in food.
Sublimation: The change of state from ice to water vapour or water vapour to ice. Unpackaged frozen
material changes to gaseous form e.g. dry ice(frozen carbon dioxide)when exposed to extreme cold air.
Dehydro-freezing : Is pre-treatment given prior to freezing, involving partial removal of water
Freeze burn: It refers to a defect which develops during frozen storage. Moisture loss due to sublimation
from surface leads to discoloration in form of patches of light coloured tissues. This can be controlled by
humidification or lowering of storage temperature or better packaging.
Antifreeze: Chemical substances that added to a liquid to lower its freezing point. These chemicals prevent
freezing and are commonly used in coolants for aeroplanes and automobiles.
Cool storage: The temperature in cool rooms where surplus food is stored is usually around 15 o
C.
Enzymatic & microbial changes in the foods are not prevented but slowed down considerably. Root crops,
potatoes, onions, apples and similar foods can be stored for limited periods.
Cold store or chilling (0 to 50
C): Chilling temperatures are obtained by mechanical refrigeration. Fruits,
vegetables and their products can be preserved for a few days to many weeks. The best storage temperature
for many foods is slightly above 00
C but this varies with the product. Besides temperature, the relative
humidity can affect the preservation of the food.
Commercial cold storages (temp.2-5 0
C; R.H 90-100%) with automatic control of temperature are used for
storage of semi-perishable foods such as potatoes and apples and made their availability throughout the year.
The growth of bacteria, yeasts, and moulds, and rate of all chemical reactions is slow at or below 100
C, and
becomes slower the colder it gets.
1 tonne of refrigeration is the rate of heat removal required to freeze a metric ton (1000 kg) of water
at 0°C in 24 hours.

Preservation by High Temperature :-Pasteurization, Sterilization, and Canning: their
Definition, Method, advantages and disadvantages
PASTEURIZATION
Pasteurization is a comparatively low order of heat treatment, generally at a temperature below the
boiling point of water. The more general objective of pasteurization is to extend product shelf-life from a
microbial and enzymatic point of view. This process is named after the French chemist Louis Pasteur, who
devised it in 1865 to inhibit fermentation of wine. He discovered that the destruction of bacteria can be
performed by exposing them to certain minimum temperature for certain minimum time and the higher the
temperature the shorter the exposure time required. In this process, all of the bacteria (such as E.coli,
Lysteria, and Salmonella) are not destroyed; but there concentration reduces very low. Refrigeration keeps
the bacteria from further growth, very low. The term pasteurization as applied to market milk today refers to
process of heating every particle of milk to at least 63° C for 30 minutes or 72° C (161°F) for 15 seconds (or
the temp-time combination which is equally efficient) in an approved and properly operated equipment.
Pasteurization : A process of heating every particle of milk or milk product to specified temperature and
holding at that temperature for specified period followed by immediate cooling and storage at low
temperature.
OR
when food is heated in containers or by other method to a temperature below 1000
C for a definite period of
time, the process is known as pasteurization
Temperature/time treatment in pasteurization
Food Product Temp (°C) Time (Seconds)
Milk 72 15
Tomato Juice 118 60
Fruit Juice 88 15
Soft Drink 95 10
Pasteurization temperature and time will vary according to:
nature of product; initial degree of contamination;
Pasteurized product storage conditions and shelf life required
Aim of Pasteurization
It inactive the food enzymes like blanching.
it kill the pathogenic organisms and inactive the spoilage micro-organisms
It increase the shelf life of the food product
Pasteurization is frequently combined with another means of preservation - concentration,
chemical, acidification, etc. Blanching is a type of pasteurization usually applied to vegetables mainly to
inactivate natural food enzymes. Depending upon time and temperature treatment there are three kinds of
pasteurization processes.

Low Temperature Long Time (LTLT)
In LTLT the time and temperature generally 62.8 °C for 30 minutes is used but may vary between
63° to 66° C or more, depending on holding time. This process is also called batch type pasteurization and
now a day this process is not used because of high energy and time loss..
In LTLT pasteurization it is possible to define three phases:
heating to a fixed temperature;
maintaining this temperature over the established time period
(= pasteurization time);
Cooling the pasteurized products: natural (slow) or forced cooling.
Advantages of LTLT
Low initial cost
Disadvantages of LTLT
Transfer of heat very slow.
Processing cost is high
Require more space for increasing capacity.
Packing can not be start during pasteurization
This is a typical batch method where a quantity of milk is placed in an open vat and heated to 63°C
and held at that temperature for 30 min. Sometimes filled and sealed bottles of milk are heat-treated in
shallow vats by that method and subsequently cooled by running water.
High Temperature Short Time (HTST)
In HTST pasteurization generally 71.7° for 15 seconds is used but according to the nature of product
the temperature may very between 85° to 90° C or more, depending on holding time.
Typical temperature/time combinations are as follows:
88° C for 1 minute
100° C for 12 seconds
121°C for 2 seconds.
Advantages of HTST
Less floor space is required
lower initial cost
milk packing can start as soon as pasteurization begin
easily cleaned and sanitized
lower operating cost
Pasteurization capacity can be increased at nominal cost.
Disadvantages of HTST
The system is not well adapted to handling small quantities of removal liquid milk product.
Gas kit require constant attention for possible damage and lake of sanitation
complete damage is not possible
Ultra High Temperature (UHT) Processing Treatments

In this method fluid is exposed to a brief, intense heating, normally to temperatures in the range 135-
140 °C but for a very short time, a second or less. The treatment kills all microorganisms. This is method is
not for very heat sensitive products because this much of temperature can spoil the product. This method is
used mainly for coffee creamers and boxed juices. After this is done, there is no need to refrigerate, because
it sterilizes the product. Sometimes the products can have a "cooked" taste that can be detected after being
brought to such a high temperature.
Sterilization
Sterilization: A process to heat food product to a specific temperature for a specific time to kill the most
heat resistant spore-forming organism.
Sterilization is a process of heat application above 100°C, by sterilization we mean complete
destruction of micro-organisms. Because of the resistance of certain bacterial spores to heat, this frequently
means a treatment of at least 121° C (250° F) of wet heat for 15 minutes or its equivalent by using steam
under pressure. It also means that every particle of the food must receive this heat treatment. If a can of food
is to be sterilized, then keeping it at 121° C or retort for the 15 minutes will not be sufficient because of
relatively slow rate of heat transfer through the food in the can to the most distant point. In such cases time
needs to be increased.
At 121° C temperatures the spores of the heat resistant bacteria are quickly killed. The longer is the
heat treatment time at lethal temperatures, the larger is the number of killed microorganisms. At higher
temperature, the shorter is the time required to kill microorganisms and lower is heat-included damage to
food products. But in the case of canned food keeping it at 121° C or retort for the 15 minutes will not be
sufficient because of relatively slow rate of heat transfer through the food in the can to the most distant
point. In such cases time needs to be increased.
Theoretically, absolute sterility does not exist. In commercial practice not all cans of food are sterile.
However, they usually do not spoil because conditions in the container are not favorable for the growth of
concerned microorganisms. The pH may be too low or absence of oxygen. Therefore, the term processing is
highly suitable than the term ‘sterilization’ applied to canned foods.
The foods products low in acid and often high in protein and contain spore forming bacteria are
difficult to sterilize. The acidity of fruits and tomatoes greatly lower the death or sterilizing temperature,
which usually explains why acid fruits are easily sterilized.
This process wills make the treated product safely preserved at room temperature.
Effect of commercial sterilization
The destruction of nutrients the thermal process is dependent on
i) time temperature treatment used as the basis of the process
ii) rate of heat transfer into the product.
The commercial developments have focused primarily on increasing the rate of heat transfer into the
product. Hence, agitated retorts such as the orbitort, steritort, flame sterilizer and hydrostatic cooker have
been developed.
It has been observed that retention of vitamin C in tomato juice is improved when processing is
conducted at a HTST condition.Under HTST conditions nutrient retention may be greatly enhanced. HTST
aseptic canning also results in a significant improvement in organoleptic qualities i.e. colour, taste and
aroma. In an evaluation of HTST aseptic processing, it was found that thiamin retention was significantly
greater in HTST products than in conventionally canned and retorted products.
It is a misconception to think that commercially sterile products remain unchanged during storage.
This is not the truth. Organoleptic and nutrient changes do occur during storage, the extent of the changes
being dependent on the time and temperature of storage. It has been observed that low temperature storage
results in an improvement in nutrient retention.

Canning
There are several methods of preservation of fruits and vegetables and canning is one of them. It is
an important method of food preservation by heat. In this process, the foodstuff (fruits & vegetables) are
placed in containers, and sterilized by placing them in hot water or steam. Canning is also known as
appertizing in honour of its inventor.
Canning : is defined as preservation of foods in sealed containers and usually implies heat treatment as the
principal factor in the prevention of spoilage.
Or
the process of preserving food by sterilization at >1000 C and cooking in a sealed metal can, which destroys
bacteria and protects from contamination.
History of Canning
The canning process dates back to the late 18th century in France when the Emperor Napoleon
Bonaparte, concerned about keeping his armies fed, offered a cash prize to whoever could develop a reliable
method of food preservation. Nicholas Appert conceived the idea of preserving food in bottles, like wine.
After 15 years of experimentation, he realized if food is sufficiently heated and sealed in an airtight
container, it will not spoil. Peter Durand, took the process one step further and developed a method of
sealing food into unbreakable tin containers, which was perfected by Bryan Dorkin and John Hall, who set
up the first commercial canning factory in England in 1813. More than 50 years later, Louis Pasteur
provided the explanation for canning’s effectiveness when he was able to demonstrate that the growth of
microorganisms is the cause of food spoilage.
CANNING PROCESS FOR FRUITS AND VEGETABLES
Canning is defined as the preservation of foods in the sealed containers and usually implies heat
treatment as the principal factor in prevention of spoilage. Mostly the canning is done in tin cans but other
containers like glass, plastics, etc. The fruits and vegetables used for canning should be as fresh as possible
so that their quality could be retained. Fruits should be mature, firm ripe and free from all defects, while
vegetables should be usually tender.
Principles
1. Destruction of spoilage organisms within the sealed containers by application of heat,
2. To improve the texture, flavour and appearance by cooking, and
3. To stop recontamination of food during storage.
Selection of fruits & vegetables
Sorting & Grading
Washing
Peeling
Cutting
Blanching
Filling
Syruping/Brining

Lidding /Clinching
Exhausting
Seaming
Processing
Cooling
Storage
Selection of Fruits and Vegetables
We should select the fresh good quality fruits and vegetables for canning because quality of canned product
is dependent on the quality of raw material. Fruits should be firm, mature and uniformly ripe. Over-ripe,
insect infected and diseased fruits and vegetables should be rejected. Unripe and immature fruits should be
rejected because they generally shrivel and toughened on canning. Vegetables should be tender. Fruits and
vegetables should be free of dirt.
Sorting and Grading
We should see that any spoiled, blemished, injured fruit or vegetable be discarded. Raw material should be
sorted based on maturity and ripeness. Fruit and vegetables should be graded according to size and colour to
obtain uniform quality of canned product. Grading can be done by hand or by machines. Screw type and
roller type grader are generally used. Fruits like berries, cherries, grape and plum are graded whole, while
peach, pear, apricot, mango, pineapple, etc., are generally graded after cutting into pieces.
Washing
Fruits and vegetables should be washed with water thoroughly. Washing will remove dust, dirt and any
sprayed chemical residue. Any microorganism over the surface of the fruits or vegetables are also washed
out. Water used for washing may be cold or hot. We may employ chlorine (150ppm) or potassium
permanganate (dilute solution) in water to disinfect fruits and vegetables. Fruits and vegetables are generally
soaked in water tank before washing by hand. They can be washed by spraying water, which is the most
effective method.
Peeling
Washed fruits and vegetables are prepared for canning. The fruits and vegetables are peeled by hand with
knife or machine, heat treatment or lye solution. Lye is a solution of caustic soda. For example, peaches and
potatoes are scaled in steam or boiling water and put in cold water to soften and loosen or cracking of skin.
Later the skin can easily be removed by hand or pressure spray of water. In case of lye peeling of fruits and
vegetables, e.g., peaches, apricots, orange and sweet potatoes are dipped in boiling lye (1-2% caustic soda)
for ½ to 2 minutes. Any trace of alkali is removed by washing fruits and vegetables in running cold water;
sometimes they are also washed in water containing 0.5 per cent citric acid or hydrochloric acid.
Cutting
We should cut the fruits and vegetables depending upon the requirement like slice, dice, finger etc either by
knife or by machine. At the same time seed, stone and core are also removed by special coring knife.
Blanching
In blanching operations the prepared fruits and vegetables are kept in boiling water or exposed to steam for 2
to 5 minutes followed by cooling in running cold water. The time and temperature of blanching vary
depending on the type of raw material. Inactivation of peroxidase enzyme is used as an index adequacy of
blanching.
The purposes of blanching are:
(1) to inactivate the enzymes, which cause discoloration and off-flavour
(2) to reduce the volume by shrinkage, making their packing easier

(3) to reduce the microbial load on raw materials
(4) to enhance the green colour of vegetables like peas and spinach,
(5) to remove undesirable acids and astringent taste of the peel resulting improved flavour, and (6) to
remove occluded gases for reducing strain on the seam of can during processing.
Filling
Tin cans are used as containers for canning. The cans can be opened from any end as they are called open
top sanitary can. Cans are washed with hot water. Prepared fruits and vegetables are filled into cans either by
hand or by machine. Plain cans are used generally, although in case of coloured fruits like black grapes, red
plum, strawberries, etc., lacquered cans are employed. In case of canned fruits the drained weight should not
be less than 50% and for berry fruits not less than 40%. Similarly for canned vegetables the drained weight
should not be less than 55% but in case of tomatoes limit is the 50%. Therefore, fruits and vegetables are
filled about 60 percent of the filling capacity of a can.
Syrup
A solution of sugar in water is called syrup. Generally the fruits are covered with sugar syrup. Cans are
filled with hot (79°–82°C) sugar syrup, leaving a headspace of 0.3 to 0.5cm. Syrup of 10° to 55° Brix (per
cent sucrose) is generally used. We can prepare sugar syrup of 20° Brix by dissolving 250 g sugar in one-
liter water and of 50oBrix by dissolving one kg of sugar in one litre water. Sometimes citric acid and
ascorbic acid are also mixed with the syrup to improve flavour and nutritional value, respectively. The
purpose of adding syrup to fruits is
(1) to improve taste
(2) to fill up the interspaces in can
(3) to facilitate further processing.
Brining
Brine is a solution of common salt in water. Brine is used in canning of vegetables. A brine of 1 to 3% salt is
used at 79°-82°C, leaving a headspace of 0.3 to 0.5 cm in the can. The objectives of brining are to improve
the taste of vegetables and to facilitate further processing by filling the interspaces of vegetables in the can.
Lidding or Clinching
Now the filled cans are covered loosely with the lid before exhausting. It has some disadvantages such as
spilling of the contents and toppling of the lids. In modern canning, lidding has been replaced by clinching
operation. In this case, lid is partially seamed. The lid remains sufficiently loose to permit the escape of
gases, air and vapour formed during exhausting operation.
Exhausting
There are respiratory gases and air remains in the cans, which are to be removed before processing. The
method of removing these gases is known as exhausting. Containers are exhausted by heating or
mechanically. In heat exhausting, the cans are passed through a tank of hot water or exhaust box under
steam. The fruit cans are exhausted at 82 to 100°C for 7-10 minutes or until temperature at the centre of the
can reaches 74°C. The vegetable cans are exhausted at 90 to 100°C for 7-10 minutes or until temperature at
the centre of the can reaches 77°C. The proper exhausting reduces the strain on the seam of the can. The
time and temperature of exhausting vary with the size and contents of can, but it should be sufficient to
ensure a vacuum of 12 to 15 inch Hg in processed and cooled can.
Sealing or Seaming
After exhausting, the cans are sealed by double seaming machine and the method is called seaming. In
sealing lids on cans, a double seam is created, and the method of sealing or closing is also known as
seaming.
Processing
Process of heating and cooling of canned food to inactivate bacteria and to preserve food is also called as
commercial sterilization. Many bacterial spores are heat resistant, which can only be killed either by very

high or by very low temperature treatment or prolonged cooking. Such drastic treatment, however, affects
the quality of food. Thus processing time and temperature should be adequate to eliminate all bacterial
growth. We must not over-cook the canned foods otherwise it will spoil the flavour, appearance and texture
of the product. All fruits and acid vegetables can be processed satisfactorily at a temperature of 100°C, i.e.,
in boiling water. The acid present in fruits and acid vegetables retards the growth of bacteria and spores.
These bacteria and spores do not thrive in heavy sugar syrups, which are normally used in canning fruits.
Vegetables, generally non acidic (except tomato and rhubarb), are processed at a higher temperatures of
about 115 to 121°C. Bacterial spores usually do not grow below pH 4.5 as you have read in previous
chapters. We, generally process the canned products having pH less than 4.5 in boiling water but products
with pH higher than 4.5 require processing at 115 to 121°C. The higher temperature can be obtained by
processing in a retort under a pressure of 0.70 to 1.05 kg/cm2 (10 to 15 lb/sq. inch). The centre of can should
attain these high temperatures. The temperature and time of processing vary with the size of the can, the
larger the can, the greater is the processing time. Fruits and acid vegetables are generally processed in open
type cookers, continuous non-agitating cookers and continuous agitating cookers. The open cookers are
galvanized iron tank of desired capacity. Sealed cans are placed in iron crates and immersed in the tank
containing boiling water. In continuous cookers, the cans travel in boiling water in crates carried by
overhead conveyors. In continuous agitated cookers, the cans are rotated by special mechanical devices to
agitate the contents of the cans. Agitation reduces the processing time considerably. The non-acid vegetables
are processed under steam pressure in closed retorts. The sealed cans are placed in the retort, keeping the
level of water 2.5 to 5.0 cm above the top of the cans. The cover of the cooker is then screwed down tightly
and the cooker is heated by steam to the desired temperature. The period of processing (sterilization) should
be counted from the time the water starts boiling or steaming. After heating for the required period, heating
is stopped and the petcock or vent is opened. When the pressure comes down to zero the cover is removed
and the cans are taken out.
Cooling
After processing, the cans are cooled rapidly to about 39°C to stop the cooking process. Cooling can be done
by several methods such as
(1) immersing the hot cans in tank containing cold water
(2) spraying cold water
(3) turning in cold water into the pressure cooker,
(4) exposing the cans to air. Generally the first method is practiced.
Cooling water may be kept sterile with 1 or 2 per cent chlorine. If canned products are not cool immediately
after processing, the quality is deteriorated, e.g., peaches and pears become dark in colour, tomatoes turn
brownish and become bitter in taste, while peas become mashy with a cooked taste.
Testing for Defects
Before the canned products are marketed, we should test them for any defect. The finished cans are tested
for leak or imperfect seals. We should tap the top of the can with a short steel rod. A clear ringing sound
indicates a perfect seal, while a dull and hollow sound shows a leaky or imperfect seal. Leaky cans should
be removed from the lot.
Storage, labeling and packing
Before storage, the cans should be completely dry, small traces of moisture are likely to induce rusting. They
should be stored in a cool and dry place. Storage of cans at high temperature should be avoided, as it
shortens the shelf life of the product. The high temperature may lead to hydrogen swell and perforation
during extended storage. The basement stores are useful, especially during summer months. The temperature
in these stores is lower by about 6° to 8°C, compared to outside temperature. Before dispatch, the cans are
labeled and packed either in wooden or cardboard boxes, and are ready for marketing. The cans may be
stored for 1 to 2 years depending upon the type of raw materials used and the shelf life of the product.
Spoilage in Canned Fruits and Vegetables

Canned products are liable to spoilage for various reasons. Spoilage in canned food may be caused due to
two reasons. Heated canned foods may undergo spoilage either due to chemical or biological reasons.
A) Spoilage due to physical and chemical changes:
1. Swell – Swell or bulge in cans caused due to the positive internal pressure of gases formed by microbial
or chemical action. Hydrogen Swell – This type of swelling is due to the hydrogen gas produced by the
action of food acids on the metal of the can. The swelling ranges from flipper – springer, soft swell or hard
swell.
2. Overfilling – Overfilling should be avoided.
3. Faulty retort operation – It gives cans look like swells.
4. Under exhausting – It causes severe strain during heat processing.
5. Paneling – It is seen in large sized cans that the body is pushed inward due to high vacuum inside.
6. Rust – Rust is mostly seen under the label and subsequently affects the label. Cans lacquered externally
do not rust.
7. Leakage – Cans generally leak due to defective seaming and nail holes.
8. Bursting – Can burst due to excess pressure of gases produced by decomposition of the food.
9. Discoloration – This may be due to enzymatic and non – enzymatic browning. Enzymatic discoloration
can be avoided by placing the peeled and cut pieces of fruits and vegetables in 2% salt solution.
10. Stack burning – The contents in the can if remain hot for a long time during storage result in stack
burning. It may cause discoloration. To avoid stack burning cans should be cooled quickly to about 39oC
before storage.
B) Spoilage by microorganisms
The time gap between filling and heat processing may cause microbial spoilage. If cans are not processed
properly they may result in spoilage by bacteria and the spoilage is termed as “Under processed” spoilage.
Clostridium botulinum a Major Threat in Canned Products
Various spoilages caused due to different microorganisms are:
1. Flat sour – The non-acid vegetables spoiled by Bacillus coagulens and Bacillus sterothermophilus.
2. Thermophilic acid spoilage – Cans swell due to production of carbon dioxide and hydrogen by
Clostridium thermo-saccharolyticum.
3. Sulphide spoilage – Caused by Clostridium significance in low acid foods.
Tin Containers for canning
The cans are made of thin steel plate of low carbon content, lightly coated on both sides with tin metal.
Sometimes discolouration of the product or corrosion of the tin plate takes place. In order to avoid
corrosion, these cans are coated inside and or outside with lacquer, the process is known as “lacquering”.
There are two types of lacquers used.
1. Acid-resistant-Acid-resistant lacquer is golden colour enamel, cans coated with it are called R enamel or
A.R. cans. The lacquered cans are used for packing fruits having water soluble colour (anthocyanins) for
example raspberry, strawberry, red plum, coloured grapes, pomegranate, etc. Fruits having water insoluble
colour, for example pineapple, mango, grapefruit, etc., are packed in plain cans only.
2. Sulphur-resistant – This lacquer is also of a golden colour, cans coated with it are called C. enamel or
S.R. cans. These cans are used for packing pea, corn, lima beans, etc. The tin cans are supplied to the
canning factory in flattened form, where they are reformed using a machine, reformer, into cylindrical
shape. After that, they are flanged by using flanger, which curls the rings outwards at each end. The one end
of the cylindrical can is then fixed, before filling it, using a machine known as double seamer. After filling,
processing and exhausting the can, the lid is fixed using the same machine.

KEY WORDS
Canning: It is a process of preservation achieved by thermal sterilization of a product held in hermetically
sealed containers
Blanching: dipping of fruits or vegetables in boiling water or exposing these to steam for a few minutes to
kill enzymatic and biological activity prior to processing.
Canning: process of sealing of foodstuffs hermetically (air tight) in containers and sterilizing them by heat
for long storage.
Degradation: loss of quality.
Denaturation: structural change in proteins due to effect of heat, light, changes in pH etc.
Deterioration: includes adverse changes in organoleptic quality, nutritional value, food safety, asthetic
appeal, colour, texture and flavour.
Pasteurization: when food is heated in containers or by other method to a temperature below 1000 C for a
definite period of time, the process is known as pasteurization.
Or
Process of heating food product to a specific temperature for a specific time to kill the most heat resistant
vegetative pathogen.
Or
Pasteurization is one type of preservation by heat mainly liquid, below boiling point for a specific time to
destroy harmful bacteria.
Sterilization: A process to heat food product to a specific temperature for a specific time to kill the most
heat resistant spore-forming organism.
D-value: It is also called “decimal reduction time” or “thermal death rate” and defined as time (in minutes)
at a particular temperature (°C) required to kill 90 percent of a microbial population.
Spoilage microorganism: Microorganism which spoil the product by developing undesirable flavours,
odours and changing food appearances or textures via microbial action.
Pathogenic: Microorganism which may infect plants, animals and man and make them sick.
Evaporation, concentration, drying and dehydration, types of dryers, advantages and disadvantages,
selection of dryers.
EVAPORATION PROCESS:-

Evaporation is a heating process in which water is removed from the liquid substance. The simplest kind of
evaporation process is, water evaporates from the sea and leaves salt behind. Other example of evaporation
occurs when we boil sugar and water solution continuously the syrup converted into a hard sugar ball. This
is because of evaporation of water. The goal of evaporation is to vaporize most of the water from a solution
which contains the desired product. Evaporation is one of the most important unit operations in food
processing. Large quantities of fruit and vegetable juices, sugar, and syrups are concentrated in several types
of commercial evaporators. In the food industry a raw material contains more water than is required in the
final product. When the foodstuff is a liquid, the easiest method of removing the water, in general, is to
apply heat to evaporate it. Evaporation is thus a process that is often used by the food technologist.
Typical process applications:
Food and dairy products,
Whey or milk proteins,
Fruit and vegetables juices,
Various extracts,
Fine chemicals evaporation.
Distillery industries
Brine concentration
Textile industry
Coffee extracts
Pharmaceutical products.
Evaporators: -
An evaporator is a device used to turn the liquid form of a chemical into its gaseous form. The liquid is
evaporated, or vaporized, into a gas. Many types of evaporators and many variations in processing
techniques have been developed to take into account different product characteristics and operating
parameters.
Single effect evaporator
TYPES OF EVAPORATORS: The more common types of evaporators include:-
Batch pan Evaporators
Forced Circulation Evaporators
Rising film Evaporators
Falling film Evaporators

Rising/Falling film Evaporators
Batch pan evaporator: - The batch pan evaporator is one of the simplest and oldest types of evaporators
used in food industry. Now-a-days it is outdated technology, but it still used in a few limited applications,
such as the concentration of jams and jellies where whole fruit is present and in processing some
pharmaceutical products.
Natural Circulation: - In Natural Circulation evaporators, short vertical tubes, typically 1-2 m long and 50-
100 mm in diameter, are arranged inside the tubes, and the product is concentrated.
Rising-film Evaporators:-These are considered to be the first 'modern' evaporator used in the industry. The
rising film principle was developed commercially by using a vertical tube heated from the outside with
steam. Liquid on the inside of the tube is brought to a boil, with the vapor generated forming a core in the
center of the tube. As the fluid moves up the tube, more vapors are formed resulting in a higher central core
velocity those forces the remaining liquid to the tube wall.
Falling film Evaporator:-The falling-film evaporators have a thin liquid film moving downward under
gravity on the inside of the vertical tubes. The design of such evaporators is complicated by the fact that
distribution of liquid in a uniform film flowing downward in a tube is more difficult to obtain than an
upward-flow system such as in a rising- film evaporator. This is accomplished by the use of specially
designed distribution or spray nozzles. The falling-film evaporators allow a greater number of effects then
the rising-film evaporator. The falling-film evaporator can handle more viscous liquids than the rising film
type. This type of evaporators is best suited for highly heat sensitive products such as orange juice.
Rising/falling-filling Evaporator: - In the rising/falling evaporator, the product is concentrated by
circulation through a rising-film section followed by a falling-film section of the evaporator. The product is
first concentrated as it ascends through a rising tube section, followed by pre-concentrated product
descending through a falling-film section; there it attains its final concentration.
Concentration
There may be some or many reason of concentration of food. The concentration of food is based upon the
fact that many foods contain a large percentage of free water. Concentration is the process which is used not
preserve the food and oin some cases it facilitate next step of processing. Like In dehydration the early
stages of water removal, moisture can be more economically removed in highly efficient evaporators than in
dehydration equipment. Concentration can be a form of preservation but this is true only for some foods.
Nearly all liquid foods which are dehydrated are concentrated before they are dried because
Some concentrated foods are desirable components of diet in their own right. For example, concentration of
fruit juices plus sugar yields jelly.
Many concentrated foods, such as frozen orange juice concentrate and canned soups , are easily recognized
because of need to add water before they are consumed.
Benefits:
Concentration reduces weight and volume and results in immediate economic advantages.
It is prior to concentrate the liquid food before dehydration because in the early stages of water removal,
moisture can be more economically removed in highly efficient evaporators than in dehydration equipment.
Increased viscosity from concentration often is needed to prevent liquids from running off drying surfaces or
to facilitate foaming or puffing.
Concentrated forms have become desirable components of diet in their own right.
Methods of concentration
Solar concentration
Uses solar energy
Used to derive salt from seawater in earlier times
Being practiced today in united states in manmade lagoons
Slow process and suitable only for concentrating salt solutions
Open Cattles

Heated by steam
Being used for some jellies and jams for certain types of soups
High temperatures and long concentration times causes damage to food
Thickening and burn on of product to cattle wall gradually lower the efficiency of heat transfer and slow
concentration process
Widely used in manufacture of maple syrup
Flash Evaporators
Subdivides food material and brings it into direct contact with the heating medium to speed up concentration
process.
Superheated steam at 150°C is used
Some other Methods Changes
Thin film evaporators
Vacuum evaporators
Freeze concentration
Ultra filtration and reverse osmosis
Changes during concentration
Concentration processes that expose food to 100°C or higher temperatures for prolonged period can
cause major changes in organoleptic and nutritional properties. Also these changes are different for
different food products. Two more common changes are
Cooked flavors and
Darkening of color
Some other changes
Heat induced reactions
In case of sugar, crystallization of sugar that can result in gritty, sugar jellies or jams.
Crystallization of lactose due to overconcentration 'sandiness', in case of certain milks.
Proteins can be easily denatured and precipitated from solution due to high concentration of salts and
minerals in solution with protein.
Proteins can be easily denatured and precipitated fro solution due to high concentration of salts and minerals
in solution with protein.
The gelation of concentrated milk and other proteinacious foods.
Microbial destruction, largely dependent on temperature
Drying or dehydration
Drying is one of the oldest methods of preserving food. Today the drying of foods is still foods can be stored
for long period without any deterioration in quality. The principal reasons for this are that the
microorganisms, which cause food spoilage and decay, are unable to grow and multiply in the absence of
sufficient water and many of the enzymes which promote undesired changes in the food cannot function
without water.
Drying or dehydration is accomplished by the removal of water from the fruits and vegetables below a
certain level at which enzyme activity and growth of microorganisms is affected adversely. Both term drying
and dehydration mean the removal of water.
The term drying is generally used for drying of the produce under the influence of non-conventional
energy sources like sun and wind.
Dehydration on the other hand refers to the process of removal of moisture by the application of artificial
heat under controlled conditions of temperature, relative humidity and air flow.

The sun drying is dependent upon the elements which are beyond the strict control. It is a slow process and
thus, not suitable for many high quality products. Generally, it will not lower the moisture contents below
about 15% which is too high for storage stability of numerous products. Removal of water from foods
provides microbiological stability and assists in reducing transportation and storage costs.
PROCEDURES FOR DRYING
Drying of fruit/ vegetable involves three stages; pre-drying treatments, drying of the commodity and post
drying treatments.
Raw Material Preparation (washing, Peeling,
Preparation)
This includes selection of fruits, sorting, washing,
peeling (for some fruits and vegetables), cutting into the
appropriate form, and blanching (for some fruits and
most vegetables). Fruits and vegetables are selected and
sorted according to size, maturity and soundness. It is
then washed to remove dust, dirt, insect matter,
mould spores, plant parts and other material that
might contaminate or affect the colour, aroma, or
flavour of the fruit or vegetable. Peeling or removal of
any undesirable parts is followed by washing. The raw
product can be peeled by hand, with lye or alkali
solution, with dry caustic and mild abrasion, with
steam pressure, with high-pressure washers, or with
flame peelers.
Blanching
Blanching is a partial pre-cooking treatment in which
vegetables/ fruits are usually heated in water or in live
steam to inactivate the enzymes before processing.
Purpose of blanching
• Reduces drying time
• Removes intercellular air from the tissues
• Causes softening of texture
• Retards the development of objectionable odour and
flavour during storage by enzyme inactivation
• Retain carotene and ascorbic acid during storage
• Removes pungency (onion)
• Impart desired translucent appearance to the product.
Spreading on flat wooden trays
After blanching spreading of fruits or vegetables on trays
helps to remove excess water from the surface of raw
material.
Sulphuring
The whole fruits, slices or pieces are exposed to the fumes
of burning sulphur inside a closed chamber known as
sulphur box for 30-60 minutes.
Purpose of sulphuring
• Prevent oxidation and darkening

• Act as preservative/ antimicrobial agents
• Check the growth of moulds
• Prevent cut fruits from fermentation
• Prevent the vitamin losses
Drying/Dehydration
Dehydrated fruits and vegetables can be produced by a variety of processes. These processes differ primarily
by the type of drying method used. The selection of the optimal method is determined by quality
requirements, raw material characteristics, and economic factors. There are three types of drying processes:
• Sun and solar drying,
• Atmospheric dehydration including stationary or batch processes (kiln,
Oven, and cabinet/tray dryers) and continuous processes (tunnel, continuous belt, fluidized-bed, foam mat,
spray, drum and microwave heated dryers), and
• Sub-atmospheric dehydration (vacuum belt, vacuum drum and freeze dryers).
Sweating
Sweating is a practice of storage of dried product in bins or boxes for equalization of moisture or re-addition
of moisture to a desired level. It is used primarily with some dried fruits and some nuts (almonds and
walnuts).
Packaging
Most product are packaged after drying for protection against moisture, contamination with micro-
organisms, and infestation with insect , although some dried foods (e.g. fruits and nuts) may be held as long
as a year before packaging.
RATE OF RYING
The rate at which drying occurs has been found to show certain phases. Consider the case where water is
being removed from a solid under such conditions that the water is present as a liquid on the surface of the
solid. If hot air is passes over the surface and act as heat source, the air and water will be in direct contact, and
the resistance to heat and mass transfer will be due only to the liquid and gas films. If water is not present at
the surface, evaporation will occur beneath the surface or on a reduced surface area. Thus rate of drying
should be greatest at the beginning when water covers the entire surface of the solid. As drying proceeds, water
is no longer available at the surface and rate of drying will decrease. If we plot moisture content against time

OR rate of drying against moisture content:-
Drying Curve
Constant rate period (AB)-During the constant rate period, it is assumed that drying takes place from
a saturated surface of the material by diffusion of the water vapor. Water can move freely from the interior of
the slab to the surface to replace that lost by evaporation.
Falling rate period (BC)-The point B represent conditions where the surface is no longer capable of
supplying sufficient free moisture to saturate the air, Rate of drying is decreases. In this case factor
influencing the rate of drying is the mechanism by which the moisture from inside the material transferred to
the surface.
Equilibrium moisture content (E.C.)--At the end of falling rate period the moisture content referred to
equilibrium moisture content
Critical moisture content (C. M. C.)-At the end of constant rate period, the moisture content referred to
critical moisture content. Critical moisture content being low with non-porous materials (sand) while high
with colloidal substances.
.
ADVANTAGES OF DEHYDRATED FRUITS AND VEGETABLES
Fruits and vegetables that are properly dehydrated, particularly to a low moisture level (below 5%) have the
following advantages:
Dehydration hardly affects the main calorie – providing constituents of fruit. It leaves the mineral
content virtually unchanged.
The process is helpful in preserving the nutritive content of the final product.
Vitamin losses are no grater with dehydration than with other preservation methods.
Dried fruits and vegetables have an almost unchanged shelf-life under proper storage conditions and
there is no greater degree of bacteria, enzymatic changes, and mould actions.
Transportation, handling and storage costs are substantially lowered, and need of costly refrigeration
during transportation and storage is eliminated.
Due to their reduction in average weight of 1/7th to 1/9th of the raw material shipping and handling
weight is therefore reduced by approximately 90%.
They provide consistent product, an important modern marketing requirement.
Seasonal variation in product quality is either absent or at a minimum with low –moisture fruits and
vegetables.
They provide opportunities for maximum convenience, flexibility, and economics in production
because they can be sized, shaped, formed, etc, to fit almost any requirement. With low moisture
disposal and pollution problems.
They offer many distinctive conventional as snack products.
FACTORS AFFECTING DRYING
Food dehydration involves two steps
to get heat into the product

to get moisture out of the product.
Surface area
The heat and mass transfer is affected by surface area and higher surface area result into increased rate of
drying. Therefore, the food to be dehydrated is sub divided into small pieces or thin layers which speeds
drying for two reasons. First larger surface area provides more surfaces in contact with the heating medium
and thus, more surface area from which moisture can escape. Second smaller particles or thinner layers
reduce the distance through which heat must travel to the centre of the food and reduce the distance through
which moisture in the centre of the food must travel to reach the surface and escape.
Air velocity
High velocity air, in addition to taking up moisture will sweep it away from the drying foods surface,
preventing the moisture from making a saturated atmosphere which would slow down subsequent moisture
removal.
Dryness of the air
When the food dried in air, then food will dried rapidly due to more absorption and more holding capacity of
moisture by dry air than the moist air. Moist air is closer to saturation and so can absorb and hold less
additional moisture, the extent of dryness of the air also determines how a low moisture content food
product can be dried to low moisture content. Dehydrated food is hygroscopic and each food has own its
equilibrium relative humidity. Equilibrium relative humidity (ERH) is the humidity at a given temperature
where the food will neither lose moisture to the atmosphere nor pick up moisture from the atmosphere.
The removal of moisture from a food product is one of the oldest preservation methods. By reducing
the water content of a food product to very low levels, the opportunity for microbial deterioration is
eliminated and the rates of other deteriorative reactions are reduced significantly.
A dryer (or drier) is a machine or apparatus used to remove moisture. It may be a small laboratory
oven taking a few grams of moist material or a large industrial unit handling tones of wet feed per hour.
However, there are three principal factors that define the nature of a dryer:
The method of material conveyance through the drying section;
The method of heating the material;
The pressure and temperature of operation.
The systems we will describe are representative of the systems used for dehydration of foods.
Classification of Dryers:
Classification of dryers on the basis of the mode of thermal energy input is the most useful to
identify some key features of each class of dryers.
Direct dryers
This type of dryers also known as convective dryers. In direct dryers, the drying medium contacts the
material to be dried directly and supplies the heat required for drying by convection; the evaporated moisture
is carried away by the same drying medium. Drying gas temperatures may range from 50º C to 400º C
depending on the material.
Indirect dryers
This involve supplying of heat to the drying material without direct contact with the heat transfer medium,
i.e., heat is transferred from the heat transfer medium (steam, hot gas, thermal fluids, etc.) to the wet solid by
conduction. Vacuum operation also eases recovery of solvents by direct condensation thus alleviating
serious environmental problem.
SELECTION OF DRYERS
Selection of the best type is a challenging task. A wrong dryer for a given application can give a loss not
only to cost but also quality and quantity of product. Note that minor changes in composition or physical

properties of a given product can influence its drying characteristics, handling properties. Following
information is necessary to select a suitable dryer:
Dryer throughput; mode of feedstock production (batch/continuous)
Physical, chemical and biochemical properties of the wet feed as well as desired product specifications;
expected variability in feed characteristics
Upstream and downstream processing operations
Moisture content of the feed and product
Quality parameters (physical, chemical, biochemical)
Safety aspects, e.g., fire hazard and explosion hazards, toxicity
Value of the product
Need for automatic control
Toxicological properties of the product
Turndown ratio, flexibility in capacity requirements
Type and cost of fuel, cost of electricity
Environmental regulations
Space in plant
For high value products like pharmaceuticals, certain foods and advanced materials, the cost of dryer
is not an important factor.
Drying of food and biotechnological products require GMP (Good Manufacturing Practice) and
hygienic equipment design and operation. Such materials are subject to thermal as well as microbiological
degradation during drying as well as in storage.
If the feed rate is low (< 100 kg/h), a batch-type dryer may be suited. Note that there is a limited
choice of dryers that can operate in the batch mode.
Tray or Cabinet Dryers
These types of drying systems use trays or similar product holders to expose the product to heated air in an
enclosed space. The trays holding the product inside a cabinet or similar enclosure are exposed to heated air
so that dehydration will proceed. Air movement over the product surface is at relatively high velocities to
ensure that heat and mass transfer will proceed in an efficient manner. A cabinet dryer can be operated under
vacuum for heat-sensitive materials or when solvents must be recovered from the vapor. The reduction in
pressure reduces the temperature at which product moisture evaporates, resulting in improvements in
product quality.
. A cabinet dryer of about 1000 sq ft of tray will handle from 1000 to 1500 pounds of fresh
prepared vegetables every 6 or 7 hours.
In most cases, cabinet dryers are operated as batch systems and have the disadvantage of non-
uniform drying of a product at different locations within the system. Improper loading of trays can also
cause poor distribution of drying air and hence poor dryer performance. These dryers require large amount
of labor to load and unload the product. Normally, the product trays must be rotated to improve uniformity
of drying.
Applications

Tray dryers are used for diverse drying applications like food, electrodes, bakery, plastic & powders and
drying of pigments.
Tray dryer is used in the industries where drying and heating are the essential parts of the manufacturing
process.
Thermostatic inner chamber of the dryer is fabricated using mild steel and stainless steel and its temperature
ranges from 50C to 150C.
Pneumatic/Flash Dryer
The pneumatic or ‘flash’ dryer is used with products that dry rapidly or where any required diffusion
to the surface occurs readily. Drying takes place in a matter of seconds. Wet material is mixed with a stream
of heated air (or other gas), which conveys it through a drying duct where high heat and mass transfer rates
rapidly dry the product. Applications include the drying of filter cakes, crystals, granules, pastes, sludge and
slurries; in fact almost any material where a powdered product is required. Salient features are as follows.
Particulate matter can be dispersed, entrained and pneumatically conveyed in air. If this air is hot,
material is dried.
Pre-forming or mixing with dried material may be needed feed the moist material.
The dried product is separated in a cyclone. This is followed by separation in further cyclones, fabric
sleeve filters or wet scrubbers.
This is suitable for rapidly drying heat sensitive materials. Sticky, greasy material or that which may
cause attrition (dust generation) is not suitable.
Applications
The main application are found in rubber additives, biological feed, PVC, fish meal, salt, feed, mineral
powder, coal powder, polypropylene, sodium sulfate, benzoic acid, gluten, plastic resins, potato powder,
corn gluten powder, medicines, alcohol dregs.
the mineral industry, potassium, lead or magnesium derivates,
the food industry: starch, casein,
the organic products: filter, cakes.
Rotary Dryers
The rotary dryer is a continuously operated direct contact dryer consisting of a slowly revolving
cylindrical shell that is typically inclined to the horizontal a few degrees to aid the transportation of the wet
feedstock which is introduced into the drum at the upper end and the dried product withdrawn at the lower
end . To increase the retention time of very fine and light materials in the dryer (e.g., cheese granules), in
rare cases, it may be advantageous to incline the cylinder with the product end at a higher elevation.

The drying medium (hot air, combustion gases, flue gases, etc.) flows axially through the drum either
concurrently with the feedstock or counter current. The concurrent mode is preferred for heat-sensitive
materials and for higher drying rates in general.
Applications
Rotary dryer is suitable to dry metallic and nonmetallic mineral, clay in cement industrial and coal slime in
coal mine, etc. Rotary dryer can be widely used to dry various materials, and it is simple to be operated.
Dryer is widely used in the field of building materials, metallurgist, chemical industry, cement and so on. It
can dry slag, coal powder, mining powder, clay, sand, limestone and so on.
The dryer has advantages of reasonable structure, high efficiency, low energy consumption and convenient
for transportation.
Tunnel Dryers

In tunnel dryers the heated drying air is introduced at one end of the tunnel and moves at an
established velocity through trays of products being carried on trucks. The product trucks are moved through
the tunnel at a rate required to maintain the residence time needed for dehydration. The product can be
moved in the same direction as the air flow to provide concurrent dehydration, or the tunnel can be operated
in countercurrent manner, with the product moving in the direction opposite to air flow.
The arrangement used will depend on the product and the sensitivity of quality characteristics to
temperature. The overall efficiency of the countercurrent system may be higher than the concurrent; product
quality considerations may not allow its use.
Fluidized-Bed Dryers
A second relatively new design for drying solid-particle foods incorporates the concept of the
fluidized bed. In this system, the product pieces are suspended in the heated air throughout the time required
for drying. The movement of product through the system is enhanced by the change in mass of individual
particles as moisture is evaporated. The movement of the product created by fluidized particles results in
equal drying from all product surfaces. The primary limitation to the fl uidized-bed process is the size of
particles that will allow efficient drying. As would be expected, smaller particles can be maintained in
suspension with lower air velocities and will dry more rapidly. Although these are desirable characteristics,
not all products can be adapted to the process.
Applications
Food industry: Cereals, Coffee, Grains, Animal food, Rice, Tea....
Minerals & Mining: Coal, Coke, Copper Sulphate, Limestone.......
Pharmaciuticals: Lithium carbonate, Salicylic Acid, Pancreatic Bile acid and salts.......
Chemical & Biochemical: General chemicals, Drying Agents, Ion exchange Resins.....
Spray Dryer

Spray drying
has been one of the
most energy-
consuming drying
processes, yet it
remains one that is
essential to the
production of dairy and
food product
powders. Basically,
spray drying is
accomplished by atomizing feed liquid into a drying chamber, where the small droplets are subjected to a
stream of hot air and converted to powder particles. As the powder is discharged from the drying chamber, it
is passed through a powder/air separator and collected for packaging. The dried product is then placed in a
sealed container at moisture contents that are usually below 5%. Product quality is considered excellent due
to the protection of product solids by evaporative cooling in the spray dryer. The small particle size of dried
solids promotes easy reconstitution when mixed with water. Most spray dryers are equipped for primary
powder collection at efficiency of about 99.5%, and most can be supplied with secondary collection
equipment if necessary
Applications
Food: milk powder, coffee, tea, eggs, cereal, spices, flavorings, starch and starch derivatives, vitamins,
enzymes, colorings...
Pharmaceutical: antibiotics, medical ingredients, additives
Industrial: paint pigments, ceramic materials....

Freeze-Dryer
Freeze-drying, also known as lyophilization, is a dehydration process typically used to preserve a
perishable material or make the material more convenient for transport. Freeze-drying works by freezing the
material and then reducing the surrounding pressure to allow the frozen water in the material
to sublimate directly from the solid phase to the gas phase. Because of the low temperature, low pressure,
and low drying rate, freeze drying is quite expensive compared to many other drying methods. But freeze
drying can produce high quality dried products. Thus, it is the preferred drying method for some high value
materials.
If a freeze-dried substance is sealed to prevent the reabsorption of moisture, the substance may be
stored at room temperature without refrigeration, and be protected against spoilage for many years.
Freeze-drying also causes less damage to the substance than other dehydration methods using higher
temperatures. Freeze-drying does not usually cause shrinkage or toughening of the material being dried. In

addition, flavours, smells and nutritional content generally remain unchanged, making the process popular
for preserving food.
Freeze-dried products can be rehydrated (reconstituted) much more quickly and easily because the
process leaves microscopic pores. Freeze-drying can also be used to increase the shelf life of
some pharmaceuticals for many years.
Applications
Pharmaceutical companies often use freeze-drying to increase the shelf life of the products, such as
vaccines.
In pharmaceutical industry freeze drying to produce tablets or wafers,
Instant coffee is sometimes freeze-dried, despite the high costs of the freeze-driers used.
Freeze-dried fruits are used in some breakfast cereal or sold as a snack,
From early 1970s freeze-drying is used in agriculturally based industries was in processing of crops such as
peanuts/groundnuts and tobacco.
Drum-Dryers
These may be atmospheric or vacuum, consisting of stem heated drums 2 to 6 feet in diameter to which to be
dried is applied by feeding device. The drums may be single or double. The drums revolve and before they
have to make one complete their revolution, the material is sufficiently dry to be removed by “Doctor
Blade” or scraper. The wet material is fed onto the drums by any one of several arrangements: by spray
feeding system or by perforated pipe. The feed method is depends upon the type of material being dried.
Applications
Drum dryers are mainly used to convert molten chemicals in to solid flakes. Solidified material is
thus flaked by adjustable scraper.
The dryer drum is accurately fabricated to ensure proper heating of aggregates with minimum heat
loss.
Rotary dryers are used for drying high viscosity liquids or pasty materials such as potato starches,
gelatins, adhesives and synthetic resins.
Kiln Dryers
These type dryers sometimes called “evaporators” and are used chiefly for drying apples and hops. A kiln
consists of a two story arrangement, the lower floor or cellar being provided with a stove or furnace and
fume pipe. The heating pipes of the furnaces are arranged so that the warm air is equally distributed
underneath the ceiling of the cellar. The ceiling consists of narrow slots and the air passes between the slats
into the first floor. The material to be dried is spread evenly to a depth of 4 to 8 inches on the slatted floor.
To facilitate air movement, intake ducts are cut into the lower parts of the cellar walls, and on the first floor.
The air is passed outside. Air movement, with this arrangement, depends upon the convection and of course
passage of the hot air through the material cannot be controlled.

Some kilns are therefore provided with fans. Potato requires 12 to 14 hours to dry in kiln and it is necessary
to turn the material several times during operation.
Vacuum Dryer
In vacuum drying, the product is placed inside a chamber where the pressure is reduced to produce a
vacuum. Since the total pressure of chamber and the partial pressure of the water vapor in the chamber is
also very low. This low partial pressure causes a large partial pressure difference between the water in the
product and the surroundings. Thus water moves more readily from the product to the surrounding
environment in the chamber. Drying under vacuum conditions permits drying at a lower temperature. This
characteristic of vacuum drying is very important for products that may suffer significant flavor changes at
higher temperatures. One advantage to vacuum drying is that it conserves energy. Less energy is needed for
drying, cutting down economic and environmental costs. This process work faster than other drying methods
and cutting down processing time.

Food Additives including Chemical Preservatives-Classification, functions and uses in foods
Food additives are substances which are added to food which either improve the flavor, texture, colour or
chemical preservatives, taste, appearance or function as processing aid.
Or
Food additives as non-nutritive substances added intentionally to food, generally in small quantities, to
improve its appearance, flavor, texture or storage properties.
Need for Food Additives:
1. Additives provide protection against food spoilage during storage transportation, distribution or
processing.
2. Many of these chemical additives can be manufactured so that foods can be “fortified” or
“enriched”. Potassium iodide, for instance, added to common salt can eliminate goiter, enriched rice
or bread with B-complex vitamins can eliminate pellagra, and adding vitamin D to cow milk
prevents rickets.
3. The use of food additives is to maintain the nutritional quality of food, to enhance stability with
resulting reduction in waste, to make food more attractive, and to provide efficient aids in
processing, packaging and transport.
Classification of food additives
Class of additive Function Examples
Anti-caking agents
Keep powdered products (e.g. salt) flowing freely
when poured
• Bentonite (558),
• Calcium aluminium silicate (556),
• Calcium silicate (552)
Anti-foaming
agents
Reduce or prevent foaming in foods
• Polyethylene glycol 8000 (1521),
• Triethyl citrate (1505)
Antioxidants
Retard or prevent the oxidative deterioration of
foods
• Butylated hydroxyanisole (320),
• Ascorbyl palmitate (304),
• Calcium ascorbate (302)
Artificial
sweeteners
Impart a sweet taste for fewer kilojoules/calories
than sugar
• Sorbitol (420),
• Alitame (956),
• Aspartame (951),
• Saccharin / calcium saccharin (954)
Bleaching agents Whiten foods
• Chlorine (925),
• Chlorine dioxide (926),
• Benzoyl peroxide (928)
Bulking agents
Increasing the bulk of a food without affecting its
nutritional value
• Ammonium chloride (510),
• Isomalt (953),
• Polydextrose (1200)
Colourings Add or restore colour to foods
• Curcumin (110),
• Brilliant blue FCF (133),
• Tartrazine (102)
Colour retention
agents
Retain or intensify the colour of a food • Ferrous gluconate (579)

Emulsifiers
Prevent oil and water mixtures separating into
layers
• Lecithin (322),
• Sorbitan monostearate (491),
• Ammonium salts of phosphatidic
acids (442)
Enzymes Break down foods (e.g. ferment milk into cheese)
• α-amylase (1100),
• Lipases (1104),
• Proteases (papain, bromelain, ficin)
(1101)
Firming agents
Strengthen the structure of the food and prevent its
collapse during processing
• Calcium chloride (509),
• Calcium gluconate (578),
• Calcium sulphate (516)
Flavour enhancers Improve the flavour and/or aroma of a food
• Calcium glutamate (623),
• Disodium 5′-ribonucleotides (635),
• Ethyl maltol (637)
Food acids Maintain a constant level of sourness in a food
• Acetic acid (260),
• Citric acid (330),
• Fumaric acid (297)
Flour treatment
agents
Improve flour performance in bread making
• Sodium metabisulphite (223),
• Ammonium chloride (510),
• Potassium bromate (924)
Glazing agents
Impart a shiny appearance or provide a protective
coating to a food
• Beeswax, white and yellow (901),
• Carnauba wax (903),
• Shellac (904)
Gelling agents
Thicken and stabilize various foods (e.g. jellies,
deserts and candies)
• Agar (406),
• Calcium alginate (404),
• Carrageenan (407)
Humectants Prevent foods from drying out (e.g. dried fruits)
• Glycerin or glycerol (422),
• Lactitol (966),
• Oxidised polyethylene (914)
Mineral salts Improve the texture of a food (e.g. processed meats) • Cupric sulphate (519)
Preservatives
Protect against deterioration caused by
microorganisms
• Sodium nitrate (251),
• Benzoic acid (210),
• Sodium benzoate (211)
Propellants Gases which help propel a food from a container
• Carbon dioxide (290),
• Nitrogen (941),
• Nitrous oxide (942)
Sequestrants
Bind and remove unwanted minerals that cause
oxidation
• Potassium gluconate (577)
Stabilisers Maintain the uniform dispersion of substances in a
food
• Xanthum gum (415),
• Guar gum (412),

• Bleached starch (1403)
Thickeners Improve texture and maintain uniform consistency
• Tannins (181),
• Sodium alginate (401),
• Pectins (440)
Vitamins Restore vitamins lost in processing and storage
• B vitamins, including niacin
• Vitamin C
• Vitamin E
Caffeine and other GRAS (generally recognized as safe) additives such as sugar and salt are not required to
go through the regulation process.
Preservatives
Definition:
A preservative is defined as any substance which is capable of inhibiting, retarding or arresting the
growth of microorganisms of any deterioration of food due to microorganisms, or of marking the
evidence of any such deterioration.
The inhibitory action of preservatives is due to their interfering with the mechanism of cell division,
permeability of cell membrane and activity of enzymes. Pasteurized squashes, cordials and crushes have a
cooked flavour. After the container is opened, they ferment and spoil within a short period, particularly in a
tropical climate. To avoid this, it is necessary to use chemical preservatives.
Chemically preserved squashes and crushes can be kept for a fairly long time even after opening the
seal of the bottle. The preservative used should not be injurious to health and should be non-irritant. It
should be easy to detect and estimate.
According to Prevention of Food Adulteration (PFA) Act (1954) and Food Standards and Safety Act
(FSSA) of 2006, a ‘preservative’ means a substance which when added to food, is capable of inhibiting,
retarding or arresting the process of fermentation, acidification or other decomposition of food.
Preservatives may be anti-microbial preservatives, which inhibit the growth of bacteria and fungi, or
antioxidants such as oxygen absorbers, which inhibit the oxidation of food constituents. Common anti-
microbial preservatives include calcium propionate, sodium nitrate, sodium nitrite and sulfites (sulfur
dioxide, sodium bisulphite, potassium hydrogen sulphite, etc.) and ethylenediamine tetra acetic acid
(EDTA). Antioxidants include butylated hydroxy anisole (BHA) and butylated hydroxy toluene (BHT).
Sulphur dioxide (including sulphites) and benzoic acid (including benzoates) are among the principle
preservatives used in the food processing industry.
Under PFA (1954) and FSSA (2006), preservatives are classified into two classes Class I and Class II
preservatives
Classification of food preservatives:
Class-I preservatives (Natural Preservatives) Class-II preservatives (Artificial
Preservatives)
Naturally occurring substances, generally used
in kitchen
Man-made chemical substance
No restriction or limitation on use as naturally
occurring
Used in limited quantity
No need to be cautious in using them, so better
to choose product containing these type of
preservatives
Risk in use as they are chemicals
includes salt, vinegar, salt, vegetable oil, honey,
sugar and wood smoke
Sorbic acid- sodium, potassium & calcium salts,
Nisin, Benzoic acid, Nitrates / nitrites

As Class 1 preservatives are natural, there is no need to be cautious while using it. On the other hand, some
risk is involved when using Class II preservatives as they are chemicals. Example, in respect of foods like
ham, pickled meat,
Permissible limits of Class II preservatives in food products (FPO)
Chemical
preservative
Concentration (ppm) Foods
Sorbic acid and its
salts (calculated as
sorbic acid)
50 Nectars, ready to serve beverages in bottles/pouches
selling through dispenser
100 Fruit juice concentrates with preservatives for
conversion in juices, nectars for ready to serve
beverages in bottles/ pouches selling through
dispensers
200 Fruit juices (tin , bottles or pouches)
500 Jams, jellies, marmalades, preserve, crystallized
glazed or candied fruits including candied peels fruit
bars
Benzoic acid and
its salts
120 Ready to serve beverages
200 Jam , marmalade, preserve canned cherry and fruit
jelly
250 Pickles and chutneys made from fruits or vegetables
600 Squashes, crushes fruit syrups, cordials, fruit juices
and barley water or to be used after dilution;
Syrups and sherbets
750 Tomato and other sauces; Tomato puree and paste
Sulphur dioxide 40 Jam , marmalade, preserve canned cherry and fruit
jelly
150 Crystallized glace or cured fruit (including candied
peel)
350 Squashes, crushes fruit syrups, cordials, fruit juices
and barley water or to be used after dilution; Syrups
and sherbets; Fruit and fruit pulp
2000 Dehydrated vegetables
Sodium and/ or
Potassium nitrite
expressed as
Sodium nitrite
200 Pickled meat
Lactic acid No limit Fermented meat, dairy and vegetable products, sauces
and dressings, drinks.
Citric acid No limit Fruit juices; jams; other sugar preserves
Acetic acid No limit Vegetable pickles; other vegetable sauces, chutney
Class-I Preservative /Natural preservatives:
Sodium chloride: Salts stop the growth of microorganisms and interfere with the action of proteolytic
enzymes. Salts also cause food dehydration by drawing out water from the tissue cells. Salt is employed to
control microbial population in foods such as butter, cheese, cabbage, olives, cucumbers, meat, fish and
bread.

The amount of salt added determines the extent of protection afforded to the food. In the preservative action
of NaCl, there is synergistic action with other intrinsic factors such as PH or extrinsic factors such as
temperature, partial pressure of oxygen etc.,
Sugar: Sugar acid in the preservation of products in which it is used. The high osmotic pressure of sugar
creates conditions that are unfavorable for the growth and reproduction of most species of bacteria, yeasts
and moulds. The preservative action of moderate strength of sugar can be improved if invertase is used to
increase the concentration of glucose relative to sucrose.
Foods in which sugars aid preservation include syrups and confectionary products, fondant fillings in
chocolate, honey, jellies, marmalades, conserves and fruits such as dates, sultanas and currants.
Vinegar (4% Acetic acid): Acetic acid (CH3COOH), in the form of vinegar, has been used to preserve
pickled vegetables from antiquity. Acetates of sodium, potassium and calcium, are used in bread and other
baked foods to prevent ropiness and the growth of moulds, but they do not interfere with yeasts.
The acid is also used in foods, such as mayonnaise and pickles, primarily for flavor but these products also
benefit from the concurrent anti-microbial action. The anti-microbial activity of acetic acid increases as the
pH decreases. Vinegar is also a good disinfectant against Salmonella, Listeria and Staphylococcus. E. coli
O157:H7 can tolerate a much more acidic environment than other organisms, but vinegar can be effective
against it as well.
Class-II Preservative /Chemical preservatives:
Sulphur Dioxide: It is used in the treatment of fruits and vegetables before & after dehydration to extend
the storage life of fresh grapes, prevents the growth of undesirable microorganisms during wine making, and
in the manufacture of fruit juices. It has good preserving action against bacteria and moulds and inhibits
enzymes, etc.
Sulphur dioxide is also the most useful agent for the prevention of browning reactions in dried fruits
and prevents enzymatic browning is most cut fruits. In addition, it acts as an antioxidant and bleaching
agent. These properties help in the retention of ascorbic acid, carotene and other oxidizable compounds. It is
generally used in the form of its salts such as sulphite, bisulphate and metabisulphite.
Potassium metabisulphite (K2O2So2 (or) K2S2O5) is commonly used as a stable source of So2. It is
fairly stable in neutral (or) alkaline media. When added to fruit juice (or) squash it reacts with the acid in the
juice forming the potassium salt and So2 which is liberated and forms sulphurous acid with the water of the
juice.
SO2 has a better preservative action than sodium benzoate against bacteria and moulds. It also retards
the development of yeasts in juice, but cannot arrest their multiplication, once their number has reached a
high value.
So2 gives a slight taste and colour to freshly prepared beverages but these are not serious defects if
the beverage is diluted before drinking. The toxicity of So2 increases at high temperature. Hence its
effectiveness depends on the acidity, pH, temperature and substances present in fruit juice.
According to FPO, the maximum amount of So2 allowed in fruit juice is 700 ppm, in squash, crush
and cordial 350 ppm and in RTS and nectar 100 ppm.
Advantages of using So2 are
• It has a better preserving action than sodium benzoate against bacterial fermentation.
• it helps to retain the colour of the beverage for a longer time than sodium benzoate.
• being a gas, it helps in preserving the surface layer of juices also.
• being highly soluble in juices and squashes, it ensures better mixing and hence their preservation any
excess of So2 present can be removed either by heating the juice to about 71o
C or by passing air
through it or by subjecting the juice to vacuum. This causes some loss of the flavoring materials due
to volatilization, which can be compensated by adding flavours.
Disadvantages of using So2 are
It cannot be used in the case of some naturally colored juices like those of jamun, pomegranate, strawberry,
coloured grapes, plum etc. on account of its bleaching action.

Organic acid: - Various acid like, benzoic acid, sorbic acid, etc. are used as chemical preservatives in
pickles, sauces, syrup, soft drink etc.
• Sorbic acid: It is found in the mountain ash berries. Sorbic acid (CH3-CH = CH – CH = CH –
COOH) and its sodium and potassium salts inhibit moulds and yeasts, in foods such as cheese, baked
products, fruit juices, wines and pickles. The antimicrobial action of sorbic acid is due to its
inhibitory influence on various enzymes in the microbial cell. The enzymes inhibited by sorbic acid
include the following:
1. Enzymes involved in carbohydrate metabolism such as enolase and lactate dehydrogenase.
2. Enzymes of citric acid cycles such as malate dehydrogenase, isocitrate dehydrogenase,
ketoglutarate dehydrogenase, succinate dehydrogenase, and fumerase.
3. Several enzymes containing SH group, and other enzymes such as catalase and peroxidase. The
antimycotic action of sorbic acid is due to the inability of moulds to metabolize the conjugated
unsaturated structure.
• Propionic acid: Propionic acid (CH3CH2COOH) and its sodium and calcium salts exert
antimicrobial activity against moulds and some bacteria. The acid finds extensive use in bakery field,
where it not only inhibits moulds effectively but is also active against the ropy bread organism
Bacillus mesentericus. The toxicity of propionic acid to moulds and certain bacteria is related to the
inability of the organisms to metabolize the three-carbon unit.
• Benzoic acid: Benzoic acid is widely used as an antimicrobial agent. Its sodium salt is more soluble
in water than the free acid and hence it is generally used. Sodium benzoate is nearly 170 times as
soluble as benzoic acid; pure sodium benzoate is tasteless and odourless. The antibacterial action of
benzoic acid is increased in the presence of Co2 and acid e.g.Bacillus subtilis cannot survive in
benzoic acid solution in the presence of Co2.
Benzoic acid is more effective against yeasts than against moulds. It does not stop lactic acid
and acetic acid fermentation. The quantity of benzoic acid required depends on the nature of the
product to be preserved, particularly its acidity. In case of juices having a pH of 3.5-4.0, which is the
range of a majority of fruit juices, addition of 0.06 to 0.10% of sodium benzoate has been found to be
sufficient. In case of less acid juices such as grape juice at least 0.3% is necessary.
According to FPO its permitted level in RTS and nectar is 100 ppm and in squash, crush and
cordial 600 ppm. In the long run benzoic acid may darken the product. It is, therefore, mostly used in
colored products of tomato, jamun, pomegranate, plum, watermelon, strawberry, coloured grapes etc.
It cannot be used for juices which are to be packed in tin containers because it not only
corrodes the tin causing pinholes, but also forms H2S which has a disagreeable smell and reacts with
the iron of the tin container to form a black compound, both of which are highly undesirable.
Nitrites and Nitrates. (NaNO2 and NaNO3)
Nitrates or nitrites are added as a preservative, antimicrobial agent or colour fixative to processed foods such
as meats and cheese. It also gives contribution in flavor. Nitrite is added in the food as an antioxidant.
Nitrate also occurs naturally in water, vegetables and plants. Nitrite when added in the food as preservative
they combine with feradoxine of the microorganism so the action of this protein stopped and due to which
ATP synthesis stopped in the microbial cell. The human body converts nitrate in food into nitrite. Nitrite
has been implicated in a variety of long term health effects, including gastric cancer.
Mode of Action
Nitrate is reduced by bacteria in the meat to nitrite, which is further reduced to nitric oxide (NO), a
compound that reacts with heme (the pigmented iron-containing non-protein part of the hemoglobin
molecule.) or iron-sulfur groups.
In meat, NO reacts with the heme in myoglobin to form nitrosohemochrome which gives meat a red color.

In bacteria, NO reacts with and destroys and iron-sulfur enzyme, ferredoxin, that is involved in ATP
synthesis. Without ferredoxin, the cells cannot synthesize energy and die.
Nisin
Nisin is a polycyclic antibacterial peptide produced by the bacterium Lactococcus lactis used as a
food preservative. In the food industry, nisin is obtained from the culturing of L. lactis on natural substrates,
such as milk or dextrose, and is not chemically synthesized. Nisin is used in processed cheese, meats, and
beverages.
In foods, it is common to use nisin at levels ranging from 1-25 ppm, depending on the food type and
regulatory approval.
As a food additive, nisin has an E number of E234. Used in processed dairy foods and low acid
canned foods. (Some true antibiotics are used in other countries)
Useful properties:
• nontoxic to humans
• “natural”
• heat stable (at low pH)
• good storage stability
• doesn’t create off odors or flavors
• no cross resistance to other clinical antibiotics, no clinical applications
Use in low acid canned foods (e.g. green beans) allows a dramatic reduction in heat processing time and
temp-gives increased quality to the food. Use in U.S. is limited to pasteurized process cheese spreads to
prevent botulism.
Harmful effects of Synthetic Preservatives on Health
Class II preservatives, the synthetically manufactured ones, can sometimes cause adverse reactions in
humans. Here are 6 chemical preservatives that you may not want to consume.
1. Sulfites are often found in wines and dried fruits. They can cause allergies, asthma, headaches and
other severe allergies. They also destroy B1.
2. Nitrates are found meats and cheeses, but are also found in fertilizers and rodent poison. High levels
of nitrate consumption have been linked to cancer, brain tumors, leukemia and Blue Baby Syndrome.
3. Sodium Benzoate is used to preserve soda, juice, pickles, salsa and cosmetics. It is linked to
hyperactivity in children and when combined with Vitamin C it becomes a carcinogen. This
chemical occurs naturally in very small amounts in some fruits.
BHA and BHT are found in fats, oils, snacks, cereals, and instant potatoes. These are known to be Vitamin
K antagonists, impair blood clotting in animals, cause tumors in the forestomach and liver of animals and is
considered a tumor promoter. Fat tissues absorb and accumulate BHT and has been seen to cause “abnornal
cellular behavior and increased liver weights” .
Tertiary butyl hydroquinone (TBHQ) is added to vegetable oils and some animal fats. Consuming high
amounts of the preservative can cause nausea, vomiting, dizziness, and hyperactivity in children.

Preservation of foods by Radiation – Irradiation of foods, Radiation doses for
spices, onions, potatoes and meat.
FOOD IRRADIATION
The exposure of food material under lower doze of radiation which are less damaging to the food is
known as irradiation.
OR
Irradiation: It is the process of preserving the food by ionizing gamma-rays, X-rays and electrons. It
destroys the microorganisms and inhibits the biochemical changes.
Food irradiation is a physical process like drying, freezing, canning and pasteurization. Food can be
irradiated wet, dry, thawed or frozen. The irradiation of food can be considered to a method of ‘cold
Sterilization’, i.e. food is free of microorganisms without high temperature treatment without changing in
texture and freshness of food unlike heat.
In fact you will not be able to differentiate between irradiated and non-irradiated food on the basis of colour,
flavour, taste, aroma or appearance. Irradiation increases the shelf life of food up-to 2 to 5 years. The
product must be frozen to achieve stability without major off-flavours. As like chemical
fumigants/preservatives irradiation does not leave any toxic residue in treated foods. Irradiation can be used
on packed food commodities. It cannot eliminate already present toxins and pesticides in food.
In 1983, the FDA approved irradiation as a means of controlling microorganisms on spices, and in
1985, the FDA widened the allowed uses of irradiation to additional foods such as straw basics, poultry,
ground beef and pork.
Purpose of food irradiation
It retards ripening or senescence of raw fruits and vegetables
Delay sprouting of potatoes
Act as a fumigant to control the insect in grains, fruits and vegetables.
Irradiation increases the shelf life of foods by destroying food spoilage microorganisms and also inhibits the
activity of food enzyme.
Kinds of Ionizing Radiations
These high energy radiations can change atoms into electrically charged ions by knocking out an
electron from the outer orbit and thus, are called ionizing radiations. These are represented in the equation
below:
RH ------------------RH+ + e− Ionization
RH ------------------R + H Dissociation
RH ------------------RH+ Excitation

But, at dose levels approved for food irradiation, these radiations cannot penetrate nuclei and thus, food can
never become radioactive. Other types of radiation energy with longer wavelengths are infrared and
microwaves.
Infrared radiation is used in conventional cooking. Microwaves, due to their relatively longer
wavelength, have lower energy levels but are strong enough to move molecules and generate heat through
friction.
Three types of ionizing radiations are approved to be used for food irradiation.
Electron beams generated from machine sources operate at a maximum energy of 10 MeV.
X-rays generated from machine sources operate at a maximum energy of 5 MeV.
Gamma rays are emitted from Co-60 or Ce-137 with respective energies of 1.33 and 0.67 million electron
volts (MeV).
Electron beams
Electron beams are streams of very fast moving electrons produced in electron accelerators. For your
better understanding, an electron beam generator is comparable to the device at the back of TV tube that
propels electrons into the TV screen at the front of the tube.
Electron beams have a selective application in food irradiation due to their poor penetration. They
can penetrate only one and one half inches deep into the food commodity. As a result, shipping cartons (pre-
packed bulk food commodities) are generally too thick to be processed with electron beams.
Electron beams are generated through machine sources, so they can be switched on or off at will and
require shielding.
X-rays
X-rays are also generated
through machine sources. X-rays are
photons and have much better
penetration and are able to penetrate
through whole cartons of food
products. X-rays are produced by
reflecting a high-energy stream of
electrons off a target substance
(usually one of the heavy metals eg. a
tungsten or tantalum metal plate), X-
rays are generated which pass through
the metal plate and penetrate the food
product conveyed underneath. But, remember that this X-ray machine is a much powerful version to the
machine used in many hospitals and dental clinics. Since X-rays are generated through machine sources, so
they can be switched on or off at will and require shielding.
Gamma rays
The third type of ionizing radiations approved for food processing are gamma rays that are produced
from radioisotopes either Co-60 or Ce-137.
As like electron beams and X-rays, radioisotopes cannot be switched off or on at will and they keep on
emitting gamma rays. Radioisotopes require shielding. Co-60 source is kept immersed under water when it
is not in use and Ce-137 is shielded in lead. Due to their continuous operation, radioisotopes need to be
replenished from time to time. Gamma rays are photons and have deep penetration ability.
Units of Irradiation
The units used to measure the effects of radiation are gray and sievert in accordance with
recommendations of International Organization for Standardization (ISO). Formerly, units used for
measuring radiation were the rad and the rem.

But now irradiation energy that a food absorb is measured in unit called gray (Gy). This is equal to one joule
of energy absorbed per kg of matter being irradiated. 1 Gy corresponds to 100 rad. practically, the dose is
generally range from 50 gray to 10000 gray depending on the food. If we relater it to heat than 10000 gray
or 10 kilo gray is equal to amount of the energy required to raise temp of water by 2.4 degree c.
Mechanism of Inactivation of microroganism
Radiation is an effective means of destroying both pathogenic and nonpathogenic bacteria as well as
parasites and viruses. Radiation, whether ionizing or nonionizing (i.e., a photon of energy or an electron),
inactivates microorganisms by damaging a critical element in the cell, most often the genetic material. Large
and complicated molecules or macromolecules, such as nucleic acids are directly or indirectly responsible
for significant spoilage. Ionization slightly modifies or breaks their structure and thus prevents these
molecules from functioning normally.
When potatoes are irradiated, the macromolecules responsible for initiating sprouting are ionized by the
gamma rays. The very complexity of these large molecules, which makes them no active, also makes them
no sensitive. One slight change to their structure, and they can no longer perform properly. Therefore, very
low exposures of gamma radiation are necessary to inactivate the macromolecules responsible for sprouting.
The most important uses of irradiation are the destruction or reduction of pathogenic bacteria in foods. The
life and reproduction of these microorganisms is dependent upon their nucleic acids, DNA
(deoxyribonucleic acid) and RNA (ribonucleic acid). Both are very large and complicated macromolecules,
they we very sensitive to ionization. As a result, when the food is irradiated, the energy from the radiation
breaks the bonds in the DNA molecules, causing defects in the genetic instructions. The effectiveness of the
process depends also on the organism’s sensitivity to irradiation, on the rate at which it can repair damaged
DNA, and especially on the amount of DNA in the target organism:
Parasites and insect pests, which have large
amounts of DNA, are rapidly killed by an
extremely low dose of irradiation.
It takes more irradiation to kill bacteria, because
they have less DNA.
Viruses are the smallest pathogens that have
nucleic acid, and they are, in general, resistant to
irradiation at doses approved for foods.
The preservative action of ionizing radiations is in
two ways,
Direct
Indirect
In direct action, DNA absorbs radiation and is
damaged. The damage to DNA is of various types –
single strand breaks (ssb), double strand breaks (dsb) or
interchange bond formation.
In the indirect action, other molecules like water, Gamma rays excite and ionize water and other molecules
along their track, giving rise to excitation, ionization and free radicals. When a cell is exposed to ionizing
radiation, the radiation can interact with the water in a cell. When the radiation interacts with water
molecules, it can break the bonds holding the molecule together resulting in hydrogen (H+
) and hydroxyls
(OH-
) ions. These ions can then combine with other ions to form substances such as hydrogen peroxide
(H2O2) which can lead to the destruction of a cell. The OH-
ions can also attack DNA. These events
contribute a great deal to the secondary effects of gamma radiation.

Process of Gamma Irradiation
Gamma irradiation is carried out inside an irradiation chamber. The irradiation chamber is shielded
by 1.5-1.8 meter thick wall. Radiation source Co-60 is contained in slender pencil like stainless steel
casings, which in turn are contained in lead shield.
Food products pre-packed or in bulk are placed in suitable containers and carried into the irradiation
chamber with the help of automatic conveyor.
The conveyor goes through a concrete wall. This concrete wall serves as a shield and prevents radiation
from reaching the surrounding area.
Before irradiation of food products activate all safety devices.
The food containers or boxes exposed for a specific length of time that allows them to absorb a defined
radiation dose.
Gamma rays pass into the food, affect the food or target organisms present in food and leave the food.
After radiation, proper handling and processing of food should be ensured, because irradiation cannot
prevent further contamination from improper handling or processing.
Irradiators are designed with several layers of overlapping protection systems / safety devices to
detect any malfunctioning of the equipments and to protect working personnel from accidental exposure to
the radiations.
EFFECT OF IONIZING RADIATION ON NUTRIENTS
All processes cause changes in nutritional value of foods; even storage causes fresh foods to loose nutrients.
It is well demonstrated that irradiation up to 10 kGy does not cause any significant change in the nutritional
value of macronutrients, i.e., lipids, proteins and carbohydrates.
Vitamins are the most essential micronutrients present in foods. Certain vitamins like A, E, C, K and
B1 are radiation sensitive. They can be reduced by irradiation but they are similarly reduced when treated by
other food processing methods.
Irradiation may convert Vitamin C (ascorbic acid) to dehydro ascorbic acid, which is another equally usable
form of Vitamin C. Fat soluble vitamins like Vitamin D are radiation resistant and survive irradiation of
food products.
Minerals are virtually unchanged. Iron is oxidized but the nutrient value of oxidized iron is same as
that of un-oxidized iron. Other processes like freezing, thawing, storage have similar effects on iron.
So, the bottom line is that irradiation does not have any adverse impact on the nutritional content of a
person’s diet.
Any food commodity irradiated up to an overall dose of 10 kGy is safe and wholesome for human
consumption.
PRACTICAL APPLICATIONS OF FOOD IRRADIATION
From a practical point of view, there are three general application and dose categories that are referred to
when foods are treated with ionizing radiation
a) Low dose, up to 1 kGy
•Sprout inhibition in bulbs and tubers (0.03 – 0.15 kGy).
•Delay in fruit ripening (0.25 – 0.75 kGy).
•Insect dis-infestation and elimination of food-borne parasites (0.25 – 1 kGy).
b) Medium dose, 1 – 10 kGy
•Reduction of spoilage microbes to improve shelf-life of meat, poultry and sea foods under refrigeration
(1.5 – 3 kGy).
•Elimination of pathogenic microbes in fresh and frozen meat, poultry & sea foods (3 – 7 kGy).
•Reduction of microbes in spices to improve hygiene (10 kGy).
c) High dose, 25 – 70 kGy

•Elimination of viruses.
•Sterilization of packaged meat, poultry and their products which are shelf stable without refrigeration (25 –
70 kGy).
•Sterilization of hospital diets for immuno compromised patients.
•Food for astronauts in space.
Radiation doses for
Spices
Spices, herbs and vegetable seasonings are valued for their distinctive flavours, colours and aromas.
Spices are generally decontaminated by irradiation or fumigation with ethylene oxide gas (ETO).Irradiation
is considered the most effective way to sanitize spices and the most countries have allowed it worldwide.
Irradiation at a dose between 7.5 – 15 kGy (average dose 10 kGy) has been established to effectively control
the microbiological
Delayed Ripening in Fruits
Irradiation at low dose levels (0.25 to 0.75 kGy) can delay ripening and over ripening in mature but
unripe tropical fruits like banana, mango and papaya.
Sprout Inhibition in Tubers and Bulbs
Traditionally, onions are bulk stored under ambient conditions in chawls, medas or sheds, the size
and design of which varies from region to region. During prolonged storage, losses occur due to sprouting,
desiccation and microbial rottage. The estimated losses are 30–50 per cent. Low ambient temperature and
high humidity during rainy season promote sprouting. The losses through microbial spoilage can be reduced
but sprouting can’t be checked by improving ventilation. Sprouting alone causes 25–30 per cent of total
losses. Sprouted onions shrivel faster due to increased water loss by transpiration. Some chemical sprout
inhibitors such as maleic hydrazide and isopropyl carbamate are used in temperate countries.
Cold storage at 0-1°C with low relative humidity (65-70%) is also practiced in many temperate
countries but strict temperature and humidity control is must. Moreover, cold storage is energy intensive and
expensive technique.
On the other hand, irradiation at very low dose levels (0.06-0.09kGy) inhibits sprouting when
properly cured bulbs are irradiated within 2-3 weeks of harvesting.
Potatoes cannot be stored more than 4-6 weeks at ambient temperature. They are stored in cold
storage at 2-4°C having relative humidity 85-95 per cent. Irradiation of potatoes combined with refrigeration
at 15°C can extend the storage period up to six months with minimum losses.
Sterilization of packaged meat---------25.00-70.00 kGy
Delay spoilage of meat------------------1.50–3.00 kGy

Concept of microwave heating effect on food quality
Microwaves are electromagnetic waves of radiant energy having frequency ranges from 300 MHz. to
300 GHz. corresponding to wavelength in the range of 0.001-1 m. Light is also a kind of electromagnetic
wave. The electromagnetic waves that are less than 3000GHz, is classified as radio wave. Radio wave that
has frequency of 300MHz to 300GHz (wave length of 1m to 1mm) is known as microwave and is positioned
somewhat close to FM radio and television broadcasting brands. A microwave oven heats food by passing
microwave radiation through it. Microwaves are a form of non-ionizing electromagnetic radiation with a
frequency higher than ordinary radio waves but lower than infrared light.
In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500
megahertz (2.5 gigahertz). They are absorbed by water, fats and sugars. When they are absorbed they are
converted directly into atomic motion and motion is converted into heat. Microwave ovens cook food “From
the inside out.” In microwave cooking, the radio waves penetrate the food and excite water and fat
molecules pretty much evenly throughout the food. There is no “heat having to migrate toward the interior
by conduction”. There is heat everywhere all at once because the molecules are all excited together.

Electromagnetic wave is a wave that has two elements, such as wavelength and frequency. Wave
length is about the length of top to top of the wave, frequency is number of waves that appear in a second.
The velocity of electromagnetic wave in a free space, such as vacuum and air, is constantly 300,000km per
second regardless of frequency. Wave length equals to this divided by frequency.
Microwaves, like light, travel in straight lines. They are reflected by metals, pass through air and
many, but not all types of glass, paper and plastic materials, and are absorbed by several food constituents
including water. Microwave ovens are used in many other industrial fields, e.g. pasteurization of vegetables,
Drying of paper or textiles, thermal treatment of pharmaceutical products and vulcanization of rubber.
Principle: - When microwaves pass into foods, water molecules and other polar molecules tend to align
themselves with the electric field. But the electric field reverses 915 or 2450 million times per second
(MHz.).
The molecules attempting to oscillate at such frequencies generate intermolecular friction which
quickly causes the food to heat.
The major food components - water, carbohydrates, lipids, proteins and salts (minerals) - interact
differently with MW. Because the primary mechanisms of MW heating are dipole rotation and ion
acceleration, MW interactions with foods depend heavily on salt and moisture content
For example, Water consists of two hydrogen atoms and one oxygen atom. It doesn’t have electric charge as
a whole; an oxygen atom is bounding with two hydrogen atoms at an angle of 104.5°. Those atoms take a
little charge of each minus (-) and plus (＋) to form a dipole.
In microwave, heat is generated quickly and quite uniformly throughout the mass. Foods do not heat
from the outside to the inside as with conventional heating since microwave penetration can generate heat
throughout the food mass simultaneously. The microwaves can result in very rapid heating but requires

special equipment, packaging materials, since microwaves will not pass through metal cans or metal foils.
Microwave heating produce major differences in food appearance and other properties compared to
conventional heating and reduces process time by 90%.
ADVANTAGES DISADVANTAGES
- Cooking time is short
- Destruction of nutrients is less
- No physical change of foods
- Melting process is easy
- Sterilization effect exists
- There is no flame, then treatment is easy
- Constraint with metal container
- Heat force control is difficult
- Water evaporation
- Closed container is dangerous because it could
be burst
- Surface toasting is impossible
.
ATTENTIONS IN USING MICROWAVE OVEN
1. If the container is metal spark is generated and no foods heat up.
2. If food is different in ingredients heating velocity could be different. For instance the food contained more
fat will be heat up fastly.
3. Bad influence to human body of microwave in microwave oven is nearly only the thermal effect. And safe
level of microwave is 10mW/cm2
. Leakage of microwave is mostly occurred in the gap of oven and
door. Therefore it is important to pay attentions that gap length is not differed.
Effects of microwave on food and nutrients
The use of microwave heating for food processing applications such as blanching, cooking, and
baking has a great effect on the preservation of nutritional quality of food. Furthermore, microwave heating
could significantly require less energy consumption for dehydrating food than conventional method.
Microwave heating is relatively fast compared to conventional heating since it does not depend on the
slower diffusion process in the latter. If properly used, microwave cooking does not affect the nutrient
content of foods to a larger extent than conventional heating. Most reports indicated that microwave cooking
resulted in higher moisture losses compared with conventional methods. Overall, the nutritional effects of
microwaves on protein, lipid, and minerals appear minimal. There is no report on the effects of microwaves
on carbohydrate fraction in foods. A large amount of data is available on the effects of microwaves on
vitamins.
Any form of cooking will destroy some nutrients in food, but the key variables are how much water
is used in the cooking, how long the food is cooked, and at what temperature.
Nutrients are primarily lost by leaching into cooking water, which tends to make microwave cooking
healthier, given the shorter cooking times it requires. Like other heating methods, microwaving converts
vitamin B12 from an active to inactive form. The amount inactivated depends on the temperature reached, as
well as the cooking time.
Boiled food reaches a maximum of 100 °C (212 °F) (the boiling point of water), whereas
microwaved food can get locally hotter than this, leading to faster breakdown of vitamin B12. The higher rate
of loss is partially offset by the shorter cooking times required.
Spinach retains nearly all its foliate when cooked in a microwave; in comparison, it loses about 77%
when boiled, leaching out nutrients.
Steamed vegetables tend to maintain more nutrients when microwaved than when cooked on a
stovetop.

Microwave blanching is 3-4 times more effective than boiled water blanching in the retaining of the
water-soluble vitamins folic acid, thiamin and riboflavin, with the exception of ascorbic acid, of which
28.8% is lost (vs. 16% with boiled water blanching).
In a conventional oven, the product is surrounded by hot air which heats the product from the outside
and also dries the surface. In microwave heating, the entire product is heated at the same time but the
heating may not be uniform.
In conventional ovens volatile flavour molecules can move from inside the product to the surface and
evaporate. But in microwave heated products, the surface stays moist and cooler; loss of flavour compounds
is less.
The surface of the product will also get to a higher temperature in a conventional oven. This
enhances the rate of the browning reaction on the surface, which provides not only the desirable brown
colour but also produces a large number of flavour compounds. But if a product is simply to be reheated, the
microwave can be used.
The sensory properties of vacuum-microwave-dried and air-dried carrot slices, which were water
blanched initially, received the higher ratings for texture, odour and overall acceptability as compared to the
air-dried carrot slices.
The retention of volatile components responsible for flavour was more in hot air microwave drying
compared to conventional hot air drying alone.
Due to high temperature and long drying time, volatile compounds are vaporized and are lost with
water vapour, resulting in significant loss of characteristic flavour in dried products. Case-hardening is a
common problem in dried fruits due to rapid drying. Compared with hot-air dried berries, MW-dried
cranberries have better colour, softer texture.

Aim: - Preparation of Pickle.
Theory
Pickle is an edible product preserved in a solution of common salt and vinegar. Pickles are also
prepared by fermentation, by lactic acid-forming bacteria, which are generally present in large numbers on
the surface of fresh vegetables and fruits. These bacteria can grow in acid medium and in the presence of 8-
10 % salt solution. Lactic acid bacteria are most active at 30°C.
Pickles can be prepared from fruits and vegetables like mango, lemon, amla, onion, cauliflower,
cabbage, beans, cucumber, bitter gourd, jackfruit, turnip etc.
The commercial varieties of pickles can be divided into five classes.
1. Fermented Pickle
2. Oil Pickle
3. Acid Pickle
4. Mustard Pickle
5. Brine Pickle
Requirements
Raw materials, equipment and apparatus
Fruit/vegetable, sugar, Peeler, Filter cloth / sieve, Pans of suitable size, volumetric flask, measuring cylinder,
Weighing balance, Potable water
Preservation with oil

Oil pickles are highly popular in India. They are highly spiced. In India, mustard oil, rapeseed oil,
sesame oil is generally used. The fruits or vegetables should be completely immersed in the edible oil.
Cauliflower, lime, mango and turnip pickles are the most important oil pickles. The pickle remains in good
condition for one to two years if handled properly. The fruits or vegetables should be completely immersed
in the edible oil. Cauliflower, lime, mango and turnip pickles are the most important oil pickles.
Procedure
Select mature and green mangoes of fruit/vegetables
Wash mangoes properly
Preparation: - After washing the mangoes the mangoes cut into desired size and remove kernel.
After preparation dip pieces into 2% salt solution to prevent browning.
Drain extra water and dry pieces into shade for few hours.
Now heat up the mustard oil and cool. Heat of oil reduces the strong flavour of mustard oil. After cooling
the spices in little quantity of oil mixed.
Now pieces of fruit mixed with oil.
After filler the pieces keep the jar for week in sun
After a week press the material to remove air and add remaining oil.
Store at ambient temp.
Precaution
Do not use metallic vessels.
The container should not impart any colour, taste, and flavour of its own to the pickle. Glass vessels,
stainless steel, and aluminum containers are generally used as cooking utensils.
The spoons and measuring vessels should also be of non corrosive materials
During preparation hygienic condition should be maintained.

Mango pickle: Mango pieces 1 kg, salt 150g, fenugreek (powdered) 25g, turmeric (powdered) 15 g, nigella
seeds 15g, red chilli powder 10g, clove (headless) 8 numbers, black pepper, cumin, cardamom (large),
aniseed (powdered) each 15g, asafetida 2g, mustard oil 350 ml Gust sufficient to cover pieces).
Aim: - Preparation of sauerkraut
Theory:-
Sauerkraut: It is the product of characteristic flavour, obtained by lactic fermentation of cabbage in the
presence of 2-3% of salt.
Sauerkraut or Sauerkohl is a German term which means ‘Sour Cabbage’ Sauerkraut is extensively
used in the North America (Canada and U.S.A.), Germany, Holland, France, U.K. and other European
countries. Cabbage (‘Brassica oleracea) normally grown in cold climate is found to be suitable for the
fermentation purpose.
It is the clean, sound product of characteristic flavour, obtained by full fermentation, chiefly lactic of
properly prepared and shredded cabbage in the presence of not less than 2% nor more than 3% of salt. It
contains, upon completion of the fermentation not less than 1.5 per cent of acid expressed as lactic acid.
Requirements
Fresh cabbage, salt, plastic film, weighing balance, weight, knife, wooden vat or cement tank
Procedure
Taken fresh cabbage
Cleaned, trimmed and shredded into 2-5mm size.
Filled into wooden vats or cement tanks.
Salt is added at the rate 2.25% and mixed thoroughly.
The top portion of the vat or tank is covered with plastic
Now enough weight is applied in order to make it compact and allow anaerobic conditions prevail for
fermentation. When weight is applied, the salt dissolves in the sap which is expressed by the pressure and by
osmosis it comes out from the cells.
After complete fermentation which is done for about 30 days or more until 1% lactic acid is formed.
The Sauerkraut is removed from the vat and packed in cans, glass or plastic containers. In cans the
fermented product is pasteurized at 74oC for 3 minutes.
After that Sodium benzoate or potassium meta-bisulphite is added when product is packed unpasteurized. It
is stored at + 5oC.
Precaution
Sometimes fermented products are very badly spoiled by contaminating bacteria causing off flavours and
colour and undesirable texture. To avoid these condition some parameters should be in control condition
like:
Temperature. Lower temperature around 7-10oC favours slow growth of bacteria and thus allows good
fermentation
Salt concentration
Sanitary conditions are important to control the desired fermentation. In traditional system, fermentation is
allowed for 6 months.

Aim: - Preparation of brine and syrup
Material required: - stainless steel utensils, Big spoon, sugar, salt etc
Syrup
A solution of sugar in water is called syrup. The syrups are added to fruits during canning. Cans are
filled with hot (79°–82°C) sugar syrup. Syrup of 10° to 55° Brix (per cent sucrose) is generally used. We
can prepare sugar syrup of 20° Brix by dissolving 250 g sugar in one-liter water and of 500
Brix by
dissolving one kg of sugar in one litre water. For making syrup, cane sugar, liquid glucose or invert sugar is
used but usually cane sugar is employed. Sometimes citric acid and ascorbic acid are also mixed with the
syrup to improve flavour and nutritional value, respectively.
Sugar syrup is not only used for canning but also prepared for getting desired consistency of many
fruit and other type of beverage products. For example squashes, carbonated beverages, etc. There are two
type of sugar syrup preparation methods hot process and cold process. In cold process very low temperature
is used to dissolve the sugar
Preparation of syrup
The sugar is dissolved in small quantity of water to yield heavy syrup (60-650Brix).
The cane sugar and water are heated together until a clear syrup is obtained. Heat treatment is provided
through steam. Tanks with steam heated coils or steam jacketed kettle is used for the preparation of the
syrup.
Sugar syrup is clarified by passing through cloth.
Then it is diluted to the desired degree Brix.
Brine

Brine is a solution of common salt in water. Brine is used in canning of vegetables. A brine of 1 to
3% salt is used at 79°-82°C. Dilute brines of 1 to 2 percent common salt are used during canning of
vegetables. Salt used for canning should be at least 99 % sodium chloride (NaCl) and lower purity less than
98 % should not be used.
Preparation of brine
The salt is dissolved in small quantity of water.
The slat and water are heated together.
Brine is clarified by passing through cloth.
The purpose of adding Syruping/brining to fruits is
(1) to improve taste,
(2) to fill up the interspaces in can,
(3) aid in the transfer of heat during the processing.
Aim: Preparation of Fruit Jam
Raw materials, equipment and apparatus
1. Fruit/vegetable, sugar
2. Peeler
3. Pulper
4. Filter cloth / sieve
5. Pans of suitable size
6. Heaters
7. Volumetric flask
8. Weighing balance
Chemicals and reagents
Citric acid / ascorbic acid
Potassium metabisulphite (KMS)
Sodium benzoate
Theory:
Jam: Jam is prepared by boiling whole fruit pulp with cane sugar (sucrose) to a moderately thick
consistency with out retaining the shape of the fruit.
Or
Jam is a product with reasonably thick consistency, firm enough to hold the fruit tissues in position,
and is made by boiling fruit pulp with sufficient sugar.
Jams may be made from all varieties of fruits. Good, fully matured fruits are selected, washed,
peeled. Thin skinned fruits do not require peeling such as Apricots, plums etc but stone can be removed by
machine. Fruits should be boiled in a small quantity of water and steamed and passed through pulper and
finisher to get the desired texture pulp.Most jam should be concentrated to boiling temperature of 103 to

1050C. The end points of jams boiling vary with fruit varieties, amount of sugar and some other factors. As
per FPO specification 45 parts of fruit to each 55 parts of sugar and contain 0.5-0.6% acid and invert sugar
should not be more than 40%. is used for preparation of jam.
Preparation of jam
Selection of fruit: - This is the first step in the preparation of jam. In this step ripe and deep color fruits are
chosen from a lot by shorting and grading
Washing: - After selection of fruits the fruits are washed with clean or plane running water.
Peeled: - After washing the fruit is peeled by using hot water and mechanical pilling.
Pulping: - After pilling the pulping of fruit is done with the help of pulpier in which the seeds and core are
removed.
Addition of Sugar: - 0.80 kg of sugar is added in 1kg of pulp. 150 of water may be added if necessary.
Boiling: - Pulp and sugar concentrate is boiled with continues stirring.
Addition of citric acid: - 2.5 gm of citric acid in 1kg of pulp.
Judging of end point: - By further cooking up to 105 C or 68-70% T.S.S.
Filling: - Jam is filled into sterilized bottle.
Cooling: - After filling then cooling is done 1 to 5 Degree C.
Sealing: - After waxing the bottle are sealed with the help of sealing machine.
Storage: - After sealing the last step is storing. The jam is stored at ambient temperature 25 to 30 degree C
Observations
Determine TSS, acidity, pectin
Result
Acidity of the given jam, jelly, preserve = % (w/v)
TSS of the given jam, jelly, preserve = %
PRECAUTIONS
•All equipment used in the preparation of fruit juices and squashes should be rust and acid proof.
•Copper and iron vessels should be strictly avoided as these metals react with fruit acids, and cause
blackening of the product.

Aim: - Preparation of brine and syrup

PRINCIPLES OF FOOD PROCESSING AND PRESERVATION updated

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PRINCIPLES OF FOOD PROCESSING AND PRESERVATION updated