Fdsn lec 18

Principles and methods
of food processing and
preservation
Course Title: Principles of
Food Science and Nutrition
Course No: FDSN 101
Credit hours: 2(2+0)
LECTURE NO: 18

“Food preservation is the
technique to prevent food
spoilage, food poisoning, and
microbial contamination in
food.”

1.To prevent microbial
contamination.
2.To kill pathogens.
3.To minimize food spoilage
and food poisoning

 Overcome in appropriate planning in agriculture
 Produce value-added products
 Preserve quality and nutritive values of foods
 Prevent spoilage and eliminate waste
 Provide variation on diet

 The desired level of quality
 The preservation length
 The group for whom the products are preserved

Prevention or delay of microbial decomposition of food
Prevention or delay of self decomposition of food
Prevention of damage by insects, animals, mechanical causes etc

Prevention or delay of microbial decomposition of food
 By keeping out micro-organisms (asepsis)
 By removal of micro-organisms (filtration)
 By hindering the growth or activity of micro-organisms (use of low
temperature, drying, creating anaerobic conditions or using chemicals).
 By killing the micro-organisms (using heat or irradiation).

By keeping out micro-organisms (Asepsis):
 Asepsis refers to keeping out the micro-organisms from the food by making use of either
natural covering or providing artificial covering around the food.

Natural barrier in foods include outer shell of the nuts (almond, walnut, peanut)
skin/peel of fruit and vegetables (banana, mango, citrus, ash gourd etc), shells on
eggs, skin or fat in meat, husk of ear corn etc.

Similarly packaging prevents entry of
micro-organisms in the food.
For example peach or mushroom sealed
in tin can, clean vessels under hygienic
surroundings helps in preventing
spoilage of milk during collection and
processing by keeping out the micro-
organisms.

By removal of micro-organisms
(Filtration):
 Filtration of liquid foods through bacteria proof filters is a
common method for complete removal of micro-
organisms from the foods.
 Liquid foods are passed through the filters made of
suitable material like asbestos pad, diatomaceous earth,
unglazed porcelain etc. and allowed to percolate through
either with or without nano-filtration etc. works on this
principle.

By using low temperature:
 Microbial growth and enzyme activity is retarded in
foods by storing them at low temperatures.
 The food commodities can be stored under cellar
storage (15 ºC) like root crops, potato, onion
refrigerator or chilling temperatures (0-50 ºC) like
most fruits and vegetables, meat, poultry, fresh milk
and milk products and under freezing temperature (-
18 to -40 ºC) like frozen peas, mushrooms etc.
By hindering the growth and activity of micro-organisms

By drying of food commodity:
 Removal of water from the food to a level at which micro-
organisms fails to grow is an important method of preservation.
Moisture can be removed by the application of heat as in sun
drying and in mechanical drying or by binding the moisture with
addition of sugar (as in jams, jellies) or salt (high salt in raw
mangoes) and making it unavailable to the micro-organisms.
 Examples include osmotic dehydration, dried grapes (raisins),
apricots, onion, cauliflower etc.

By creating anaerobic conditions:
 Anaerobic condition can be created by removal or evacuation
of air/oxygen from the package, replacement of air by carbon
dioxide or inert gas like nitrogen.
 Lack of oxygen prevents growth of any surviving bacteria and
their spores under such conditions.
 Production of carbon dioxide during fermentation and its
accumulation at the surface makes the conditions anaerobic to
prevent the growth of aerobes.
 Carbonation of drinks and storing fresh food under controlled
atmospheres serves the same purpose.

 Canned food in which the food is sealed
after removal of air (exhausting) illustrates
this principle.
 Anaerobic bacteria and their spores present
however, need to be killed to prevent the
food from being spoiled.
 A layer of oil on top of any food prevents
growth of microbes like moulds and yeasts
by preventing exposure to air.

By use of chemicals:
Appropriate quantity of certain chemicals added to the food can hinder the undesirable
spoilage in the food by:
Interfering with the cell membrane of the micro-organisms, their enzyme activity or
their genetic mechanism
•By acting as an anti-oxidant.
• The optimum quantity of preservative as per approved regulation need to be
used as higher concentrations can be a health hazard.

•Chemical preservatives are benzoic acid and its sodium salt, sorbic acid, potassium meta-
bi-sulphite, calcium propionates etc.
•Common antioxidants to check off flavour (rancidity) in edible oils include butyl hydroxy
anisole (BHA), butyl hydroxy toluene (BHT), tertiary butyl hydroxy quinone (TBHQ),
lecithin etc.
•Addition of organic acids like citric, acetic and lactic acid in the food inhibits the growth
of many organisms.

By killing the micro-organisms
a) Use of heat:
Coagulation of proteins and inactivation of their metabolic enzymes by
application of heat leads to destruction of micro-organisms present in
foods.
Exposure of food to high temperature also inactivates the enzymes present
in the food.
Foods can be heated either at temperature below 100 ºC (pasteurization)
at 100 ºC (boiling) or at temperature above 100 ºC (sterilization).

Pasteurization (heating below 100 ºC):
 It is a mild heat treatment given to the food to kill most
pathogenic micro-organisms and is used in the food
where drastic heat treatment cause undesirable changes
in the food.
 It is usually supplemented by other methods to prolong
shelf life.
 Pasteurization is most commonly used in treatment of
milk and other dairy products either as low temperature
high time (LTHT) or high temperature short time
(HTST) process.

•Heat treatment of milk at 62.2 ºC for 30 minutes refers to LTHT process.
•Heating at 72 ºC for 15 seconds is termed as HTST process.
•Grape wine is pasteurized at 82-85 ºC for 1 minute and beer is pasteurized at 60 ºC.
•Pasteurization of juices depends upon their acidity and method of packing whether in
bulk or in bottle or can.
•Bottled grape juice is pasteurized at 76.7 ºCfor 30 minutes while in bulk the juice is
heated to 80-85 ºC for few seconds by flash treatment.
•Carbonated juice is heated at 65.6 ºC for 30 minutes in bottles and vinegar in bulk is
held at 60-65 ºC for 30 minutes

Boiling (heating at 100 ºC): Cooking of food including vegetables, meat etc by boiling
with water involves a temperature around 100 ºC. Boiling of food at 100 ºC kills all the
vegetative cells and spores of yeast and moulds and vegetative cells of bacteria.
•Many foods can be preserved by boiling (e.g. milk).
•Canning of acid fruit and vegetables (tomatoes, pineapple, peaches cherries etc) is carried
by boiling at about 100 ºC.
•Various terms used for heating of food are baking (in bread), simmering (incipient or
gentle boiling), roasting (in meat) frying (shallow or deep fat frying) and warming up
(small increase in temperature up to 100 ºC).

Heating above 100 ºC:
 Heating by steam under pressure is used to obtain
temperature above 100 ºC by using steam sterilizer or
retort.
 The temperature in the retort increases with increase
in steam pressure.

•For canning of mushrooms and other non-acid vegetables the processing temperature of
121.1 ºC at 15 psi pressure are used.
•For sterilization of milk and other liquid foods like juices, ultra high temperature (UHT)
process is used.
•In UHT process, the food is heated to very high temperature (150 ºC) for only few seconds
by use of steam injection or steam infusion followed by flash evaporation of the condensed
steam and rapid cooling. The process is also used for bulk processing of many foods.

Use of radiation:
 Irradiation consists of exposing the food to either
electromagnetic or ionizing radiations to destroy the micro-
organisms present in the food.
 Examples of irradiation include use of ultraviolet lamps in
sterilizing slicing knives in bakeries.
 Gamma radiation from cobalt -60 or cesium 137 source have
been used for irradiation of many fruits like papaya, mango
and onion, spices, fish etc.
 They are also used for inhibition of sprouting in onion and
potatoes.

Prevention or delay of self decomposition of food
By destruction or inactivation of food enzymes (blanching or boiling):
 Blanching is a mild heat treatment given to vegetables before canning, freezing or drying
to prevent self decomposition of food by destroying enzymes.
 Blanching is carried out by dipping the food commodity either in boiling water or by
exposing than to steam for few minutes followed by immediate cooling.

By prevention or delay of purely chemical reactions (use of antioxidants to
prevent oxidation):
 Foods containing oils and fat turn rancid and become unfit for consumption
due to oxidation.
 Addition of appropriate quantity of antioxidants like butyl hydroxy anisole
(BHA), butyl hydroxyl toluene (BHT), tertiary butyl hydroxy quinone (TBHQ),
lecithin etc prevents oxidation and preserves the food.

Prevention of damage by insects, animals, rodents and
mechanical causes
Use of fumigants in dried fruits,
cereals etc checks the damage
caused by insects and rodents.
Wrapping of fruits, providing
cushioning trays, using light pack
and good packaging material checks
the damage to fresh food
commodities during handling and
transportation.

Asepsis
Removal of microorganisms
Maintenance of anaerobic conditions
Use of high temperatures
Use of low temperatures
Use of radiation
Use of chemicals
Drying
Biological methods

Asepsis is the process of prevention of growth of microorganisms and their
contaminants or both.
The covering or wrapping, prevents primarily contamination during handling,
protect the process foods from microbial contamination.

Natural protection - outer layer of animal and plant tissue protects the
inner layer free from microorganisms. This protective covering will delay /
prevent microbial decomposition e.g. shells of nuts, skins of fruits and
vegetables etc.

Packaging of foods - such as wrapping, hermetically sealed containers. This
methods will prevents primarily contamination during handling.

Sanitary methods of handling and processing foods e.g. in the dairy industry,
contamination with microorganisms is avoided as much as possible in the production and
handling of milk.

Food industries - attention is given to prevention of the contamination of foods (from raw
material finished products) concerning the "bioburden" of microorganisms on or in a food.
BIOBURDEN
Kinds of microorganisms
present whether any spoilage
or pathogenic
microorganisms.
Number of microorganisms.
Spoilage organisms- food
spoilage.
Difficult to preserve

• BY USING PRE
STERILIZED FILTERS
• EX: FRUIT JUICES, SOFT
DRINKS
FILTRATION
• NOT VERY EFFECTIVE
BECAUSE NOT ALL
MICROORGANISMS ARE
REMOVED
• EX: TREATMENT OF
DRINKING WATER
CENTRIFUGATION
• HELPFUL IN REMOVING
SOIL MICROORGANISMS
FROM FRESH FRUITS
AND VEGETABLES THAT
MAY RESISTANT TO HEAT
PROCESS DURING
CANNING
WASHING
• TRIM AWAY SPOILED
PORTIONS OF FOOD
TRIMMING

• Anaerobic conditions can be
achieved by a complete fill,
evacuation of the unfilled space,
replacement of air by C02 or N2
and others.
• Spores are resistant to heat and
may survive in canned food but
they unable to germinate in the
absence of oxygen.

 After filling the products into containers,
evacuation of the unfilled space (the head
space) and filling it by CO2 or an inert gas
such as nitrogen.
 After hot filling the products into
containers, condensation of vapor at
headspace by cooling, which reduces the
amount of oxygen in headspace and
dissolves oxygen with the product.

 Removal of air from packages or
vacuum packaging of foods by
removal of air from inside of
packages.
 During fermentation in a container or
a package; microorganisms produce
anaerobic condition due to reduction
of oxygen and production of CO2 and
H2

Fdsn lec 18

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Fdsn lec 18