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CHAPTER 4 P1: BASIC PRINCIPLES IN FOOD PROCESSING - Coggle Diagram
CHAPTER 4 P1: BASIC PRINCIPLES IN FOOD PROCESSING
Moisture Removal
Importance of Moisture Removal
The dry matter that remains after moisture removal is commonly referred to as total solids.
Determination of moisture is important economically to the processor and the consumer.
Moisture content of a food product will affect its stability and quality.
Importance of Determination of Moisture Content in Food Stuff
Legal and Labeling Requirements:
There are legal limits to the maximum or minimum amount of water that must be present in certain types of food.
Economics:
The cost of many foods depends on the amount of water they contain – water is an inexpensive ingredient and manufacturers often try to incorporate as much as possible in a food, without exceeding some maximum legal requirement.
Microbial Stability:
The propensity of microorganisms to grow in foods depends on their water content. For this reason many foods are dried below some critical moisture content.
Food Quality:
The texture, taste, appearance and stability of foods depend on the amount of water they contain.
Food Processing Operations:
A knowledge of the moisture content is often necessary to predict the behaviour of foods during processing, e.g. mixing, drying, flow through a pipe or packaging.
Moisture is a quality factor in the preservation of some products:
Dehydrated vegetables and fruits
Dried milks
Powdered eggs
Dehydrated potatoes
Spices and herbs
Reduced moisture is used for convenience in packaging or shipping of:
Concentrated milks
Liquid can sugar (67% solids) and liquid corn sweetener (80% solids)
Dehydrated products
Concentrated fruits juices
Heat Treatment
Basic purpose for the thermal processing of foods
To reduce or destroy microbial activity
To produce physical or chemical changes
To make the food meet a certain quality standard (colour, taste and flavor)
Definition:
the combination of temperature and time required to eliminate a desired number of microorganisms from a food product.
Main Temperature Categories
Blancing
Pasteurization
Sterilization
Blancing
to destroy enzyme activity in fruit and vegetables
not intended as a sole method of preservation but as a pre-treatment prior to freezing, drying and canning
Function of Blancing
Reduce surface microbial contamination
Soften vegetable tissues to facilitate filling into containers
Methods of Blancing
carried out at up to 100°C using hot water
Machine - Hot Water Blanchers
Various designs which submerge the food in hot water (70 -100°C) for a specified time before moving to a dewatering / cooling section.
Factors Influencing Blancing Time
Type of fruit or vegetables
Size of the pieces of food
Method of heating
Pasteurization
relatively mild heat treatment
widely used technique in the food industry
can be used to destroy heat sensitive microorganisms
2 Groups of Microorganisms survive pasteurization temperatures used in Milk
Thermoduric
Thermophilic
Method for Pasteurizing
1) Batch Method
2) High-Temperature Short-Time (HTST)
3) Ultra Heat Treatment / Ultra High Temperature (UHT)
Sterilization
controlled heating process used to completely eliminate all living microorganism, including thermo resistant spores in milk or other food.
Physical Methods of Sterilization
Heat Sterilization
Moist Heat Sterilization
Dry Heat Sterilization
Filtration
Irradation
Sound(Sonic) Waves
Pressure (Pascalization)
Sunlight (Solar Disinfection)
Factors affecting heat resistance of microorganism
Age of cell
Medium of growth
Moisture content
pH of medium
The length of time required to sterilize a food is influenced by:
The heat resistance of microorganisms or enzymes
The heating conditions
The pH of the food
The size of the container
The physical state of the food
Evaporation
concentration by boiling
Partial removal of water from liquid foods by boiling off water vapour.
used to pre-concentrate foods (e.g. fruit juice, milk and coffee) prior to drying, freezing or sterilization and hence reducing their weight and volume.
Low Temperature Treatment
Preservation by low temperature
temperatures to preserve foods is based upon the fact that the activities of foodborne microorganisms and enzyme reactions can be slowed down and/or stopped at temperatures above freezing and generally stopped at subfreezing temperatures.
Preservation of food by chilling
Preservation of foods at temperatures above freezing and below 15°C
used to reduce the rate of biochemical and microbiological changes and hence to extend shelf life of fresh and processed foods.
causes minimal changes to sensory characteristics and nutritional properties of foods.
Categories of chilled food
-1°C to 1°C (fresh fish, meats, sausages, smoked meat and ground meat)
0°C to 5°C (pasteurized milk, canned meat, cream, yoghurt, salad, sandwiches, baked foods, soups and sauces)
0°C to 8°C (soft fruits and fruit juices, cooked rice, hard cheese and butter)
Chilling equipments
1) Mechanical refrigerators :
circulates between the 4 elements of the refrigerator, changing state from liquid to gas and back to liquid.
2) Cryogenic system:
use solid carbon dioxide, liquid carbon dioxide and liquid nitrogen and it removes latent heat of sublimation and liquid cryogens remove latent heat of vaporization.
Effect on foods
effect of chilling on the sensory characteristics of processed foods is hardening due to solidification of fats and oils.
include enzymatic browning, lipolysis, colour and flavour deterioration and retrogradation of starch to cause staling of bread, protein denaturation, and vitamin degradation.
Superchilling
one of the method that can be used to maintain food products at a low temperature.
maintained below 0°C.
Freezing
unit operation in which the temperature of a food is reduced below its freezing point and a proportion of the water undergoes a change in state to form ice crystals.
Freezing techniques
Plate freezing
Immersion freezing
Cabinet freezing
Air blast freezing
Changes during freezing
Water in inter cellular spaces of fruits and vegetables freezes and ice-crystals are formed which cause adjacent cell walls to rupture.
causes death of 10% to 60% of the microbe population
Changes in physical aspects
1) Freezer burn :
Caused by sublimation of ice from the surface of food into the air inside the freezer. The surface of freezer burned food appears as dry, grainy, and brownish spots and the tissues become dry and tough.
2) Recrystallization :
Caused by fluctuations in the storage temperature. Causes crystals to melt partially. When temperature falls again, large sized crystals are formed resulting in loss of quality.
Changes in chemical aspects
Loss of natural pigments like chlorophyll and flavour in vegetables.
Loss in vitamic C
Advantages of freezing
Good natural colour, flavour and nutritive value can be retained.
Texture usually better than for other methods of food preservation.
Foods can be frozen in less time than they can be dried or canned.
Disadvantages of Freezing
Texture of some foods is undesirable because of changes due to the freezing process.
Initial investment and cost of maintaining a freezer is high.
Storage space is limited by how much the freezer will hold.
Acidity Control
Acidity and pH
pH scale ranges from 0 to 14 with pH 7 being neutral.
The lower the pH value, the higher the level of acidity.
Acid foods have a natural pH of 4.6 or less such as tomatoes.
Reasons for Measuring pH in Food Processing
To produce products with consistent colour, taste, texture
To efficiently produce products at optimal cost
To avoid causing health problems to consumers
To meet regulatory requirements
pH value
The difference between pH 6 and pH 5 represents a ten-fold increase in acid concentration, a change of just 0.3 represents a doubling of acid concentration.
Variations of pH can impact flavour, consistency, and shelf-life.
Checking the pH of water prior to adding it to different food processes provides a quick and simple way to guarantee the quality of the end-product.
pH plays an important role in food processing whether the objective is to make sour bread not too sour and sour lemon.
Examples of Acidity Regulators
1) Citric acid (E 330):
Mainly used as an acidity regulator as well as aroma compound
2) Calcium acetate (E 263):
Used as a thickening agent (cake mixtures, puddings, pie fillings)
3) Fumaric acid (E 297):
Acidity regulator and flavouring agent