There are two main temperature categories employed in thermal processing: Pasteurization and Sterilization. The basic purpose for the thermal processing of foods is to reduce or destroy microbial activity, reduce or destroy enzyme activity and to produce physical or chemical changes to make the food meet a certain quality standard. e.g. gelatinization of starch & denaturation of proteins to produce edible food.

1. Thermal processing of fruits and
vegetables
Ranit Sarkar
11/16/2022
Ranit Sarkar 1

2. Index
• Introduction
– Microbial contamination
– Types of bacteria in food poisoning
– Growth curve of microorganism
– Thermal processing
• Blanching
• Pasteurization
• Sterilization
11/16/2022
Ranit Sarkar 2

3. Introduction
There are two main temperature categories employed in thermal processing:
Pasteurization and Sterilization. The basic purpose for the thermal processing of foods
is to reduce or destroy microbial activity, reduce or destroy enzyme activity and to
produce physical or chemical changes to make the food meet a certain quality standard.
e.g. gelatinization of starch & denaturation of proteins to produce edible food.
11/16/2022
Ranit Sarkar 3

4. Microbial contamination
Microbial Contamination refers to the presence in the food of harmful microorganisms
which can cause consumer illness major contamination sources are
 Water
 Air
 Dust
 Equipment
 Sewage
 Insects
 Rodents
 And employees
11/16/2022
Ranit Sarkar 4

5. Types of bacteria in food poisoning
• Norovirus
• Salmonella
• Clostridium perfringens
• Campylobacter
• Staphylococcus aureus (Staph)
• Clostridium botulinum (botulism)Listeria
• Escherichia coli (E. coli)Vibrio
11/16/2022
Ranit Sarkar 5

6. Growth curve of microorganisms
11/16/2022
Ranit Sarkar 6

7. Thermal processing
Thermal processing is defined as the combination of temperature and time required to eliminate a desired number of
microorganisms from a food product .
• the term “thermal “ refers to processes involving heat .
• Heating food is an effective way of preserving .
The basic purposes for the thermal processing food is,
 to reduce or destroy microbial activity .
 Reduce or destroy enzyme activity .
 And to produce physical or chemical changes .
 To make the food meet a certain quality standard
11/16/2022
Ranit Sarkar 7

8. BLANCHING
Blanching is a unit operation prior to freezing, canning, or drying in which
fruits or vegetables are heated for the purpose of inactivating
natural/endogenous enzymes; modifying texture; preserving color, flavor,
and nutritional value; and removing trapped air.
11/16/2022
Ranit Sarkar 8

9. • Blanching serves a variety of functions! --one of the main ones
being to destroy enzymatic activity in vegetables and some fruits,
prior to further processing by heat.
• As such, it is not intended as a sole method of preservation but as a
pre-treatment which is normally carried out between the preparation
of the raw material and later operations (particularly heat
sterilization, dehydration and freezing.
• Blanching is also combined with peeling and/or cleaning of food,
to achieve savings in energy consumption, space and equipment
costs.
FUNCTION OF BLANCHING
11/16/2022
Ranit Sarkar 9

10. REACTION WITHOUT BLANCHING
11/16/2022
Ranit Sarkar 10

11. OBJECTIVE
1. Inactivate enzymes
A. Metabolic
B. Maintain color
C. Texture
D. Flavor
E. Nutritive value
11/16/2022
Ranit Sarkar 11

12. THE FACTORS WHICH INFLUENCE BLANCHING TIME
 Type of fruit or vegetable
 Size of the pieces of food
 Blanching temperature
 Method of heating.
11/16/2022
Ranit Sarkar 12

13. PASTEURIZATION:-
Invented By French Scientist Louis Pasteur in 1864.
Earlier the process was also used for beer and vinegar.
Pasteurization of milk was suggested by Franz von Soxhlet
in 1886.
Pasteurization is the process of heating usually to less
than 100 °C (212 °F), and then rapidly cooling.
In this process liquids or food in order to reduce the
eliminate of pathogenic micro-organism.
11/16/2022
Ranit Sarkar 13

14. Methods of pasteurization:-
Low temperature holding pasteurisation (LTH) Low Temperature Long
Time (LTLT), or Batch
High-temperature, short time (HTST) or continuous flow
Ultra heat treatment or ultrahigh temperature (UHT)
11/16/2022
Ranit Sarkar 14

15. Low temperature holding pasteurisation (LTH) or Batch:-
 The (LTLT) process is the traditional method of pasteurizing milk.
 In the vat the milk is heated to 62.8 C and held for 30 minutes followed by rapid
cooling.
 In this method low temperature applied for long duration .
 Its self life very shorter duration.
High-temperature, short time or continuous
flow:-
 HTST plate pasteurizer from 72*C (162*F) to 95*C (203*F) For 15 seconds.
 This Pasteurizer is a plate pasteurizer for pasteurizing milk, juice, and egg products.
 In this method high temperature applied for short duration .
11/16/2022
Ranit Sarkar 15

16. Ultraheat treatment or ultrahigh temperature
(UHT):-
This UHT method food by heating it above 130°C (275°F), the
temperature required to kill spores in milk, for 1 to 3 seconds.
UHT is most commonly used in milk production, but the process is also
used for fruit juices, cream, soy milk, yogurt, wine, soups, honey.
OTHER PROCESSES USED TO PASTEURIZED FOODS :-
* Steam Pasteurization
* Irradiation Pasteurization
11/16/2022
Ranit Sarkar 16

17. PASTEURIZED
PRODUCTS:-
11/16/2022
Ranit Sarkar 17

18. Sterilization
1. Pasteurized products :
• heat sensitive bacteria: deleted
• heat resistant microorganisms: accepted
2. Sterilization products: destruction of all bacteria including their spores.
3. Food products -> sealed containers -> exposed to temperatures above 100°C in pressure cookers.
4. Temperatures above 100°C, usually ranging from 110-121°C
5. Products are kept for a defined period of time at temperature levels required for the sterilization.
11/16/2022
Ranit Sarkar 18

19. Factors affecting Growth of Micro-organism
• Food
• Acid
• Time – Temperature
• Oxygen
• Moisture
11/16/2022
Ranit Sarkar 19

20. Nutrient Composition
• Yeast – food with simple sugar
• Molds – Capable of growth in difficult conditions
• Bacterial Pathogens – Protein Based food
Factors affecting Growth of Micro-organism
• Food
• Acid
• Time – Temperature
• Oxygen
• Moisture
11/16/2022
Ranit Sarkar 20

21. Factors affecting Growth of Micro-organism
• Food
• Acid
• Time – Temperature
• Oxygen
• Moisture
11/16/2022
Ranit Sarkar 21

22. Factors affecting Growth of Micro-organism
• Food
• Acid
• Time – Temperature
• Oxygen
• Moisture
11/16/2022
Ranit Sarkar 22

23. Factors affecting Growth of Micro-organism
Optimal temperature range for growth:
• Thermophile – thrives high temperature 41-121°C
• Mesophile – grows at moderate temperature 20-45°C
• Psychrophile – grows at low temperature 0-20°C
• Food
• Acid
• Time – Temperature
• Oxygen
• Moisture
11/16/2022
Ranit Sarkar 23

24. Factors affecting Growth of Micro-organism
• Food
• Acid
• Time – Temperature
• Oxygen
• Moisture
11/16/2022
Ranit Sarkar 24

25. aw = 0.90
Factors affecting Growth of Micro-organism
• Food
• Acid
• Time – Temperature
• Oxygen
• Moisture
aw = 0.95 aw = 0.93
aw = 0.93
11/16/2022
Ranit Sarkar 25

26. Sterilisation Process
Sterilization Phase 1 heating phase
Phase 2 Holding phase
Phase 3 Cooling phase
11/16/2022
Ranit Sarkar 26

27. Sterilisation equipment
1. Lid/Door: The lid should be sealed tightly to prevent
contamination and proper sterilization. The top is
sealed tightly with the help of an airtight screw.
2. Pressure Chamber: stain less steel , materials are
placed inside the inner part of the vessel,
3. Whistle: release the pressure of the chamber before
opening the lid after sterilizing the materials.
4. Safety valve: to avoid an accident when the pressure
inside the vessel is exceptionally high.
5. Electrical heater: heating element attached to the
jacket; that heats the water to produce steam.
6. Water releasing valve: replacing and cleaning the
water
11/16/2022
Ranit Sarkar 27

28. source 11/16/2022
Ranit Sarkar 28

29. Autoclave types
11/16/2022
Ranit Sarkar 29

30. Design of heat Sterilization Processes
• Take account of the type of microorganism (determined largely by food conductions e.g.
acidity) and its heat resistance.
• Result in an acceptably low probability of survival of spores
• Be effective in every part of the food
11/16/2022
Ranit Sarkar 30

31. Canned Food
• Shelf stable (can itself should be in good condition : no rust, dents, or swelling)
• They should be ‘commercially sterile’ (microbes incapable of growing in favorable
condition)
Types of containers
to be used
Metal containers
Glass jars
Retortable pouches
11/16/2022
Ranit Sarkar 31

32. About Services Portfolio Team Contact
Ranit Sarkar
Need presentation
assistance?
https://www.linkedin.com/in/ranit-sarkar-
83b295209/
mailto:ranitsarkar71@gmail.com
https://t.me/Ranit_0_1
https://www.youtube.com/channel/UCirfpHbkvkM
9l4K4MVYh-Pw
11/16/2022
Ranit Sarkar 32

33. Thank you
11/16/2022
Ranit Sarkar 33