This document provides information on food preservation through thermal processing. It discusses microbial contamination of food and the types of bacteria that can cause food poisoning. It then describes various thermal processing techniques used for food preservation including blanching, pasteurization, and sterilization. For each technique, it outlines the purpose, common temperature and time parameters used, and examples of equipment involved. Key factors that affect the heat resistance of microorganisms are also summarized. The document serves as an introduction to the topic of food preservation through thermal processing.

1. FE-235
FOOD PROCESSING
EQUIPMENT - I
Food Preservation by Thermal Processing
Shelke G.N
Assistant Professor
Department of Food Engineering
CFT Ashti,
Maharashtra 414202
Phone: +919561777282
E-mail: shelkeganesh838@gmail.com

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Point to be covered
 Introduction.
 Microbial Contamination.
 Thermal Processing
 Thermal Death Rate Kinetics
Of Microorganism
 Spoilage Probability
 Thermal Process Calculation

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desired separation of components
Introduction
Food Preservation
The term food preservation refers to any one of a
number of techniques used to prevent food from spoiling.
It includes methods,
 Heating/ Thermal processing
 Low temperature
 Reduction water activity
 Control storage
 irradiation,
 addition of chemical
 Non thermal processing

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Introduction
Microbial Contamination
Microbial contamination refers to the
presence in food of harmful microorganisms which can cause consumer illness
Major contamination sources are ,
 water,
 air,
 dust,
 equipment,
 sewage,
 insects,
 rodents,
 and employees.

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Introduction
Type of bacteria causes food poisoning?
 Salmonella.
 Norovirus (norwalk virus)
 Campylobacter.
 E. Coli.
 Listeria.
 Clostridium perfringens.

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Introduction
Cases of food poisoning
 Abdominal cramps.
 Diarrhea.
 Vomiting.
 Loss of appetite.
 Mild fever.
 Weakness.
 Nausea.
 Headaches.

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Introduction
some food born pathogen that cause serious illness

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Growth curve of microorganism

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Introduction
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 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.

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Types Thermal Processing
There are three main temperature categories employed in thermal
processing:
 Blanching
 Pasteurization
 Sterilization.
 Mild processes Blanching ,Pasteurisation
 More severe processes Canning, Baking, Roasting, Frying

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Blanching
The primary purpose of blanching is to destroy enzyme activity in fruit and
vegetables.
 It is not intended as a sole method of preservation,
 But as a pre-treatment prior to freezing, drying and canning.
Functions of blanching include:
 Reducing surface microbial
contamination
 Softening vegetable tissues to
facilitate filling into containers
 Removing air from intercellular
spaces prior to canning

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Methods of Blanching
 Blanching is carried out at up to 100°C using hot water
 Blanching is carried out steam
Hot Water Blanchers
o Includes various designs which hold the food in
hot water (70 to 100°C) for a specified time,
then moves it to a dewatering/cooling section.
o In this type the food enters a slowly
rotating drum, partially submerged in the hot water.

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desired separation of components
Steam Blanchers
 This is the preferred method for foods with large cut
surface areas as lower leaching losses.
 Normally food material carried on a mesh belt or
rotatory cylinder through a steam atmosphere, residence
time controlled by speed of the conveyor or rotation.
 Often poor uniformity of heating in the multiple layers
of food, so attaining the required time-temperature at the
centre results in overheating of outside layers.

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Pasteurization
Purpose of Pasteurization
 Pasteurization is a relatively mild heat treatment.
 In which food is heated to <100°c.
 It is widely used throughout the food industry.
 It can be used to destroy enzymes.
 It can be used to destroy relatively heat sensitive
Micro-organisms
 It is used to extend shelf life.

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Pasteurization
Milk Pasteurizing Temperatures
Temperature Time
63°C For 30 min (low temperature long time LTLT)
72°C For 15 sec (primary high temperature short time, HTST
method)
89°C For 1.0 sec
90°C For 0.5 sec
94°C For 0.1 sec
100°C For 0.01 sec
The two groups of micro-organisms that survive pasteurization temperatures used in milk
 Thermoduric: organisms that can survive exposure to relatively high temperatures but
do not necessarily grow at these temperatures e.g. Streptococcus and Lactobacillus.
 Thermophilic: organisms that not only survive relatively high temperatures but require
high temperatures for their growth

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Pasteurization
Method for Pasteurizing
There are number of basic methods of pasteurization.
Batch (holding) Method
 In this method every particle (e.g. milk)
must be heated to at least 63°C.
 and held for at least 30 minutes,
 however this is not used commercially
these days.

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Pasteurization
High-Temperature-Short-Time (HTST)
 In this method the heating of every particle
of milk to at least 72°C.
 and holding for at least 15 seconds.
 Carried out as a continuous process.
 Ultra Heat Treatment (UHT) a sterilization
treatment, can also be performed using higher
temperatures and shorter times e.g. 1 s at 135°C

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Pasteurization
Typical Equipment employed for
(HTST) method includes:
• Plate heat exchanger (PHE)
• Holding tube – sized to ensure the
correct treatment time is achieved
• Holding tanks – for storage of the
raw and pasteurised milk
• Balance tank – to assist in
maintaining full flow, and to take
returned milk if temperature not
Achieved
• Control and monitoring system.

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Sterilization
 Sterilization is a controlled heating process used
to completely eliminate all living micro-organisms,
including thermo resistant spores in milk or other food.
It can be achieved by,
 Moist heat,
 Dry heat,
 Filtration,
 Irradiation,
 Or by chemical methods
 The aim of sterilization is the destruction
of all bacteria including their spores.

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Sterilization
 Food products filled in sealed containers are exposed
to temperatures above 100°C.
 Temperatures above 100°C, usually ranging from
110-121°C depending on the type of product,
 Heat must be reached inside the product.
 Products are kept for a defined period of
time at temperature levels required for
the sterilization
 It depending on type of product
and size of container.

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Sterilization
The sterilization process
 The sterilization process in the canned product can be subdivided into three phases.
 Phase 1 = (heating phase) heating medium (water or steam) the product temperature is
increased from ambient to the required sterilization temperature
 Phase 2 = (holding phase) temperature is maintained for a defined time.
 (Phase 3 = (cooling phase) the temperature in the can is decreased by introduction of
cold water into the autoclave.

22. Sterilization
Sterilization Equipment
Autoclaves or retorts
 In order to reach temperatures above 100°C
(“sterilization”), the thermal treatment has to
be performed under pressure in pressure cookers,
also called autoclaves or retorts.
 In autoclaves or retorts, high temperatures
are generated either by direct steam injection,
by heating water up to temperatures over 100°C
or by combined steam and water heating.

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Thermal Death Rate Kinetics Of Microorganism
Factors affecting heat resistance of microorganism
 Age of cell, younger cell are less heat resistance
 Initial concentration of spore or cells more the number greater the heat treatment
 The medium in which growth has occurred a more nutritious medium increases heat
resistance
 Moisture content dry food tend to require more serve heat treatment during sterilization
 pH of medium cell or spore have great heat resistance at or natural pH values.

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