PASTEURISATION

BANARAS HINDU UNIVERSITY
Session :- 2022-2024
Submitted by
Kunwar Pratik Singh
Submitted to
A K Chauhan Sir
DEPARTMENT OF DAIRY SCIENCE AND FOOD TECHNOLOGY
MSc (Food technology)1st semester
Title -PASTEURIZATION

Pasteurization
 Process developed in 19th century in France by Louis Pasteur, for the preservation of wine.
 Its application resulted in new term ‘Pasteurization’.
 Louis Pasteur was pioneer in its use for the preservation of wine.
 Dr. Soxhlet of Germany introduced this process for preservation of milk in 1886.
Definition :
 Pasteurization refers to – The process of heating of every and
every particle of milk to at least 62.8°C (145°F) for 30 min. or
71.7°C (161°F) for 15 second or to any temperature- time
combination, which is equally efficient, in an approved and
properly operated equipment.
TEMPERATURE TIME
62.8°C (145°F) 30 minutes
71.7°C (161°F) 15 second
135°C to 150°C For just
(average 141°C) two second

 After pasteurization the milk is immediately cooled to 5°C or below.
 The term pasteurization is mainly applied to the market milk today.
Objectives of Pasteurization :
 To render the milk safe for human consumption by destruction by of all pathogenic
microorganism.
 To improve the keeping quality of milk by destruction of almost all spoilage organism.
 Thus, the pasteurization does not kill all micro-organisms in milk and therefore, it is not a
method of milk sterilization but it is a process of disinfection.
 Pasteurization is also intended to inactive some enzyme in the raw.

Relationship Between Time & Temperature :
 The efficiency of pasteurization depends upon time-temperature relationship.
 Initially the pasteurization temperature was set to kill Mycobacterium tuberculosis,
which was supposed to be the most heat resistant organism in milk.
 This organism get destroyed at a temperature of 140°F in 10 minutes.
 Thus, the initial temperature of pasteurization was set to 143°F (61.6°C) for
30 min.
 Latest on, it was discovered that another pathogen namely Coxiella burnetii
(causative agent of Q fever), also occurs in the milk and it is able to survive at
the milk and it is able to survive at the temperature of 143°F.
 Thus , to ensure the destruction of Coxiella, temperature of pasteurization was raised to
145° F (62.8° C).

Methods of Pasteurization
 There are methods of Pasteurization in common particle
1. Low temperature holding (LTH)
2. The high temperature short time (HTST)
3. Ultra high temperature (UTH)

1.Low Temperature Holding (LTH) :
 This is also called as low temperature – long time
(LTLT) method or batch or vat pasteurization method.
 In this, the milk is heated to 62.8°C(145°F)for 30 min
and promptly cooled to 5°C or below.
 The heating of milk in this method is carried out by
three different types of pasteurizes-
i. Water –Jacket Vat –
 This is double walled tank in which hot water or steam under
partial vacuum circulates for heating and cold water for cooling.
 The outer wall is usually insulated to reduce heat loss.
 The heat exchange takes place through the wall of the inner lining.
 The milk is agitable by slowly moving paddles or propellers.
 When heating, the vat cover is left open for escape of off- flavours, and
when holding, the cover is closed.

ii. Coil Vat Type –
 The heating or cooling medium is pumped through
a coil placed in either a horizontal or vertical
position.
 Such coil is turned through the milk.
iii. Water Spray Type-
 A film of hot water is sprayed over the surface
of the tank holding the milk.

2. High Temperature Short Time Method (HTST):
 It is the modern method of pasteurization of milk.
 Used for large volume of milk.
 In this method, of the milk is heated to 71.7°C(161°F)for 15 sec and cooled promptly to
5°C or below.
 This method gives the continuous flow of milk.
 Milk is heated either in tubes or in thin metal plates or in heat exchangers by electricity
or hot water.
 Raw cold milk is allowed to enter in heat exchange and hot, pasteurized milk is take out.
 It is comparatively faster method.
 There are different of HTST pasteurization system.

Essential Components of a Standard HTST System
1. Raw milk tank : It is a tank where chilled raw milk is stored.
2. Balance tank : It maintains a constant head for the incoming milk.
3. Milk feed pump : It creates suitable pressure that is necessary for
efficient flow.
4. Flow control system : It controls the flow rate of milk
5. Filters and clarifires : They remove the dirt (if any) from the milk.
6. Homogenizer : It divides fat globules into the micro globules
to avoid fat separation in standing milk.
7. Plate Heat Exchanger (PHE) with regarding section, heating section,
heating section and cooling sections:
It facilitates an efficient pasteurization
8. Flow diversion valves :
 They ensures that all the condition for pasteurization have been met.
 It diverts the milk to head tank if is not properly heated to
pasteurization temperature for reprocessing.
 If milk is properly pasteurized milk, it passes forward through the flow
diversion valves into the regeneration it is cooled.

Plate Heat Exchanger
 This plate heat exchanger is a compact and simple
unit.
 Its plate may be used for regeneration, heating,
holding and cooling
 A space of approximately 3 mm is maintained between
plates by a non-absorbent rubber gasket.
 These plates are designed to provide a uniform
turbulent flow of milk with heat transfer.

Regeneration (heating)-
 The raw incoming milk is partially and
indirectly heated by the outgoing milk.
 This reduce the cost of HTST process.
 For example-
• Milk entering at 4°C
• Heating in regenerator to 34°C
• Heated in heating section to 74°C
• Cooled in regenerator to 44°C
• Cooled in cooling section to 4°C
 Here the increasing from 4°c to 34°C is a change
of 30°C and the decrease from 74°C to 44°C is also
a change of 30°C
 Without regeneration, the milk would to be heated
by hot water/steam from 4°C to 74°C, a difference
of 70°C.
 With regenerative heating, however, hot water
or steam need not be used for the temperature
change between 4°C and 34°C.

 This temperature change it brought about
by use of the outgoing hot milk.
 Thus, here regeneration saves the heat.
 On the other hand, without regeneration the
milk would need to by chilled water from
74°C to 4 °C, a difference of 70 °C.
 With regenerative cooling, however, change
From 74 °C to 44 °C difference of 30 °C.
 This temperature change is brought about
by use of cold incoming milk.
 Here also the savings due to regeneration
Takes place.
 The milk to be heated flows across one side
of the plate and heating or cooling medium
flows across the other side in the opposite
direction.

Advantage of Regenerative Heating
 Utilization of the incoming chilled milk to cool the outgoing hot pasteurization milk
increasing the efficiency of the PHE.
 Smaller amount of energy is required to heat the milk to pasteurization temperature
since the heating does not start from 4°c of the chilled milk.
 Reduces the amount of time required to pasteurization.

Advantage of HTST :
 Initial cost of the method is less.
 The milk can be pasteurized quickly and effectively.
 Milk packaging can be started as soon as pasteurization beings.
 This permits more efficient utilization of labour for packing
and distribution.
 The system can be easily cleaned sanitized.
 Lower operating cost.
 Reduced milk losses.
 Development of thermophiles is not a problem.

Disadvantage of HTST :
 This system is not well adopted for small quantities milk or milk
products.
 Gaskets require constant attention for possible damage and
lack of sanitation.
 Complete drainage is not possible.
 Raw milk with thermoduric bacterial count is not efficiently
pasteurized as a compared to LTH method.

3. Ultra High Temperature Method (UTH)
 Milk is heated at 135°C to 150 °C ( average 141 °C ) for just two second or no hold
time.
 It can be carried out by direct or indirect means of heat treatment.
 Direct treatment is either injection of steam into milk or infusion of milk into a
steam chamber.
 Indirect treatment includes the use of heat exchange.
 The success of method depends on immediate aseptic packaging.
 The temperature and time combination is much more lethal to bacteria and kills
all bacteria.

UHT Pasteurization by Steam Injection Technique :
 In this, the steam in injection into the milk.
 The steam at a pressure higher than that of pressure of milk flow is injected into the milk steam
through a suitable nozzle.
 There are many different injector designs.
 In all of these, the steam and milk are kept in thermally separate zone until they reach the mixing
zone.
 This prevents the surface fouling of the injector.

UTH Pasteurization by Steam
Infusion Technique :
 It is very similar to injection system, except for
the method of mixing of milk with steam.
 The infusion is done by dropping heated milk
into a steam pressure vessel with a conical base.
 The heating is instant.
 The milk is then cooled rapidly by evaporative
cooling with exposure to a slight vacuum.
 This removes the water that is added to the milk
due to the condensation of the steam.
 Steam infusion can be used to pasteurize a variety
of dairy products like cream and special dairy
products but now it is popular for milk.

 Packing of ultra-pasteurized milk is also carried out under sterile conditions to prevent
the recontamination with spoilage bacteria.
 Ultra-pasteurization makes milk free of spoilage and harmful bacteria, but it is not
considered sterile and, thus it requires refrigeration.
 Ultra-pasteurized milks have more “cooked” flavor as compared to conventionally
pasteurized.
 Average shelf-life of ultra-pasteurized milk product is 30-90 days if held under
refrigeration and in packed condition.
 Once an the product is opened, it may become contaminated with spoilage bacteria.
 Thus, after opening, ultra- pasteurized milk should be kept well refrigerated and
consumed within 7-10 days for the best quality and taste.

Advantage of Pasteurization :
1. Pasteurized milk is safe for consumption.
2. Pasteurization is designed to decrease microbial count.
3. Pasteurization has little effect on the nutritive value of milk.
4. There is some loss of vitamin C and B group vitamins, but this is insignificant.
5. With Pasteurization, keeping quality of milk remains unaltered.
6. Pasteurization does not reduce the fat content of milk.
Disadvantage of Pasteurization :
1. Cooked taste may be developed, for which consumer may complain.
2. Pasteurization reduces cream layer of the milk.
3. Vitamin content may get changed.

Some example of Convention Pasteurization Treatments
Product Temperature Time Remark
Milk 62.8°C 30 min LTH
Milk 71.7°C 15 sec HTST
Milk 137.8°C 2sec UHT
Ice-Cream 71.1°C 30 min LTH
Ice-Cream 82.2°C 16-20 sec HTST
Grape Wines* 82-82.5°C 1 min In bulk
Fruit Wines* 62.8°C depends Bottled hot
Beer 60°C depends Bottle hot
Dried fruit 65.6-85°C 30-90 min
Grape Juice* 76.7°C 30 min
Apple juice* 85-87.5°C 30-60 min Bottled in bulk
Carbonated Drink* 65.6 30 min In common
Vinegar* 60-65.6 30 min In bulk
*Depends on the acidity

Effect On Foods
 Pasteurization is
-- mild heat treatment
-- minor changes to nutritional sensorial characteristics
 Shelf life: Few days or weeks
Effect: Colour, flavour and aroma
 Fruit Juice
-- Main problem is colour deterioration by enzymic browning
(poly phenol oxidase).
-- This browning reaction promoted by the presence oxygen.
-- In fruit juice industries, fruits are involve to deaerated prior to pasteurization
process. There for retain natural fruit colour.

 Whiteness of raw milk & pasteurized milk differs
- due to homogenization.
 Pasteurization has no measurable effect on
- the colour of milk.
 Pigments in plant & animal products are mostly
unaffected.
 Small loss of volatile aroma compounds during
pasteurization of juice.
 Volatile recovery used to produce high quality juice.

Effect : Vitamin Loss
• In Fruit Juices,
- losses of vitamin C & carotene are minimized
•Changes to milk
- 5% loss of serum protein &
- small changes to vitamin content.

Conclusion
 Raw milk does contain pathogens. As most of the microbes present
in milk are prone to cause various infections and make you sick, it is
imperative to keep them away from reaching your gut. Hence it is
necessary to subject the milk sample to a mild heat treatment before
consumption. In short, pasteurization is the process of heating milk
to a stipulated length of time at high temperatures to make milk
microbiologically safe for consumption. This in turn also leads to an
increase in shelf life and provides better quality to the milk-derived
products
 Long before refrigerators were in use, people were used to consuming
fresh food every day due to minimalistic storage options. Now with
the betterment of technology, perishable food products like milk are
eligible to be stored with an extended shelf life.

Reference
1. https://dairytechnologist.com/wp-content/cache/all/milk-
pasteurization//index.html
2. https://www.sciencedirect.com/topics/food-science/pasteurized-milk
3. https://www.britannica.com/technology/pasteurization
4. https://www.sciencedirect.com/sdfe/pdf/download/eid/3-s2.0
B9781855736764500184/first-page-pdf
5. https://www.uoguelph.ca/foodscience/book/export/html/1898
6. https://www.motherearthnews.com/real-food/pasteurize-raw-milk-at-home

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