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thermal processing of food

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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.

Published in: Engineering
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thermal processing of food

  1. 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
  2. 2. Processes which depend primarily on physical forces to accomplish the desired separation of components Point to be covered  Introduction.  Microbial Contamination.  Thermal Processing  Thermal Death Rate Kinetics Of Microorganism  Spoilage Probability  Thermal Process Calculation
  3. 3. Processes which depend primarily forces to accomplish the 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
  4. 4. Processes which depend primarily forces to accomplish the desired separation of components 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.
  5. 5. Processes which depend primarily forces to accomplish the desired separation of components Introduction Type of bacteria causes food poisoning?  Salmonella.  Norovirus (norwalk virus)  Campylobacter.  E. Coli.  Listeria.  Clostridium perfringens.
  6. 6. Processes which depend primarily forces to accomplish the desired separation of components Introduction Cases of food poisoning  Abdominal cramps.  Diarrhea.  Vomiting.  Loss of appetite.  Mild fever.  Weakness.  Nausea.  Headaches.
  7. 7. Processes which depend primarily forces to accomplish the desired separation of components Introduction some food born pathogen that cause serious illness
  8. 8. Processes which depend primarily forces to accomplish the desired separation of components Growth curve of microorganism
  9. 9. Processes which depend primarily forces to accomplish the desired separation of components 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.
  10. 10. Processes which depend primarily forces to accomplish the desired separation of components 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
  11. 11. Processes which depend primarily forces to accomplish the desired separation of components 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
  12. 12. Processes which depend primarily forces to accomplish the desired separation of components 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.
  13. 13. Processes which depend primarily forces to accomplish the 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.
  14. 14. Processes which depend primarily forces to accomplish the desired separation of components 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.
  15. 15. Processes which depend primarily forces to accomplish the desired separation of components 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
  16. 16. Processes which depend primarily forces to accomplish the desired separation of components 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.
  17. 17. Processes which depend primarily forces to accomplish the desired separation of components 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
  18. 18. Processes which depend primarily forces to accomplish the desired separation of components 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.
  19. 19. Processes which depend primarily forces to accomplish the desired separation of components 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.
  20. 20. Processes which depend primarily forces to accomplish the desired separation of componentss 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.
  21. 21. Processes which depend primarily forces to accomplish the desired separation 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. 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.
  23. 23. Processes which depend primarily forces to accomplish the desired separation 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.
  24. 24. Processes which depend primarily forces to accomplish the desired separation
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