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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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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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Processes which depend primarily forces to accomplish the
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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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Processes which depend primarily forces to accomplish the
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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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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.

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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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