Chapter 5 :- Food Processing
Food processing is the transformation of cooked ingredients, by physical or chemical means into food, or of food into other forms.Food processing combines raw food ingredients to produce marketable food products that can be easily prepared and served by the consumer.
Food processing involves the conversion of raw materials and ingredients into an acceptable food product for the consumer. It encompasses every aspect necessary to transport raw materials from the harvest site through packaging & merchandising. It involves the application of scientific principles to slow down or stop the natural process of food decay caused by microorganisms, enzymes in food or environmental factors such as heat, moisture and sunlight and thus preserving the food.
The term processing is very broad and encompassing many techniques. These include primary processing like threshing, dehusking, polishing and grinding in case of food grains and preliminary operations such as cleaning, washing, sorting, grading, peeling, blanching and cutting to produce secondary processed products like bread, biscuits, pickles, frozen meals etc.
Removal of unwanted matter from the food- Unwanted matter maybe inedible, indigestible, harmful to health. The unwanted matter is removed by appropriately designed gadgets the processes include shelling, destoning, milling, peeling etc.
Making food safe for consumption- food sometimes contain toxins which are harmful to health. These toxins need to be inactivated. eg trypsin inhibitors in soybeans, fungal toxins such as aflatoxin in mouldy groundnut & grains can be removed by visual examination. Use of processes which remove toxins, and heat to destroy microorganisms & their toxins.
Increasing digestibility- most foods are difficult to digest unless they are cooked. Cooking softens fibre, gelatinizes the starch denatures protein & makes food easier to digest.
Enhance flavour, colour and taste-The acceptability of food depends to a large extent on its organoleptic or sensory qualities. Processing techniques enhance the appearance of food and many techniques make food more appetizing and tasty such as caramelization of sugar fermentation batter, and alcoholic fermentations produce superior taste as compared to unprocessed food.
Improve texture &consistency- Processes such as emulsification, aeration, gel formation & increase in viscosity are aimed at improving the texture and consistency of ready to eat, cook-chill & freeze operations. Processing prevents changes inconsistency of such operations during the freeze-thaw process crystal foods & disable texture can be obtained.
Minimizing nutrient loss- Nutrients are better retained by controlled processing conditions such as controlled heating, autoclaving etc lost during processing are generally compensated by added synthetic vitamins. Processed foods are often enriched with vitamins, minerals & lysine.
Extending shelf life- Processing extends the shelf life, as all the processes like dehydration, cold storage, canning & pasteurization are aimed at preservation of food.
Increasing acceptability through fabricated food new products of uniform size and shape are being introduced in the market which is good for health. Health drinks like aloe vera juice is blended with tastier substances so as to increase its acceptability. Availability of ready to eat foods, extruded foods is all because of food processing techniques thus helping in new food product development.
Following are some major types of Treatment applied in Food Processing:-
- Use of Low Temperature
- Use of High Temperature
- Dehydration
- Use of Preservatives
- Controlled Atmosphere Storage
- Fermentation
- Radiation
Use of low Temperature
Low temp preserves food by retarding chemical reactions enzymatic action and growth activity of microorganism. The lower the temp the better the food will be preserved. At low temperature, microorganism is not killed and their number can multiply once the temperature becomes favourable.
- Refrigeration– Temperature of 1-4ºC prevent food from spoiling for short periods. Frozen foods kept at -18ºC can be preserved for a year. Chilling temp. retards microbial growth and biochemical changes which affect color, texture , flavor & nutritive value. Eg food such as eggs, dairy products, chicken, meat & seafood are held at chilling temp.
- Freezing- Preserves food for a longer period by reducing its temp to -18ºC or lower. At this temp water present in food is converted to ice & microbial growth stops. It retains colour, flavor & nutritive value , however texture of some foods is adversely affected. Fruits, vegetables, meat, fish & poultry.
Various techniques used for freezing are blast freezes, plate freezers, immersion freezers, spray freezers etc.
Advantage
- Prolongs shelf life without adversely affecting nutritive value & sensory quality of food.
- Controls chemical & enzymatic changes in food.
Disadvantage
- Repeated freezing & thawing are detrimental for food quality.
- Maintenance in cold chain required otherwise will lead to microbial spoilage.
Use of high-temperature
High temperature destroys micro-organism. At temp above 63ºC bacteria stop multiplying and as the temp increases, they are gradually destroyed.
- Blanching –it is a pretreatment. Foods which are to be frozen, dried or canned are immersed in hot boiling water for a few minutes prior to processing. It helps in removal of peel, inactivation of enzymes, removal of gas in tissue spaces which helps in proper filling of the can.
- Pasteurization
There are 3 methods
- Low temp holding (LTH) 62ºC for 30mins
- High temp short time (HTST) or flash method 72ºC for 15 secs.
- Ultra high temp sterilization (UHTS) temp above 135ºC for 2sec this method makes food commercially sterile. Food pasteurized – milk, fruit juries beer, wine
Canning – Temp used are above 100ºC. The temp & time required for canning depends on the type of food to be canned. All the microorganisms are destroyed by heating the food in an autoclave at a temp between 115ºC & 125ºC. This method is used to preserve fruits, vegetables, fish, meat, poultry, etc.
Cooking- Temperature attained in this procedure is 100º C. At this time microorganisms are destroyed but spores survive. Methods of wet cooking are boiling, steaming, steaming, stewing and poaching. Dry cooking are baking, roasting, grilling. Temp. of surface reaches to 115ºC.
Advantages
- Heating above 55ºC denatures enzymes, halts ripening, enzymatic browning & spoilage of food.
- Heating above 100ºC with modified pressure helps in the sterilization of food products & equipment.
Disadvantages
- Prolonged heating causes the development of burnt flavour, dark colour &loss of nutrients.
- Excessive heat denatures proteins, destroys vitamins, dries out food by removal of moisture.
Dehydration
It is the process of removal of moisture from the food. Drying is defined as the application of heat under controlled conditions to remove the majority of the water normally in the food by evaporation. The main purpose of dehydration is to extend the shelf life of foods by a reduction in water activity.
Methods used are
- Sun drying- Used for fruits like grapes, apricots etc. This methods leads to contamination.
- use of mechanical driers – food to be dried is passed on conveyor belts, hot air is passed through the food. Eg. Milk. Dried food is packed in air –tight containers immediately.
- Freeze-drying- in this method of removal of water, the product is frozen and the temp is so maintained that the water can be sublimed from the frozen state ( ice turns into vapour ). Freeze dried food needs no further refrigeration or preservation.
Advantages
- Dried products are lighter, lesser bulky, easy economical to store pack & transport.
- Have low microbial content, enzymatic actively get reduced or stopped due to loss of moisture & application of heat.
Disadvantages
- Cellular structure gets destroyed resulting in major alterations in shape, colour, texture, taste and mouthfeel.
- Certain nutrients like vitamin C, riboflavin, thiamin get destroyed.
- Rehydration or reconstitution may not always result in the production of foods which are close to their natural counterparts.
Use of Preservatives
A preservative is any substance which retards deterioration of food.
- Class I –natural – Sugar, common salt, glucose, fructose, vinegar, wood smoke. There is no restriction by law on their addition to food.
- Class II- chemicals – They are added in defined permitted limits. They are usually added at the end of the processing operation. Eg – benzoic acid, nitrates, nitrites etc.
Controlled Atmosphere Storage
It is controlling & maintaining environmental conditions in a way to reduce ripening of fruits & vegetables by
i) lowering the temp
ii) reducing available oxygen
iii) increasing carbon dioxide concentration.
Fermentation
Selected microorganisms are used giving distinctive taste, higher nutritive value & longer shelf life
Eg: alcoholic beverages such as beer & wine lactic acid fermentation in curd & yoghurt.
Advantages
- Selective and careful fermentation can help in creating new dishes and variations.
- Helps in the preservation of food & improving shelf life.
Disadvantages
- Large-scale fermentation needs to be handled carefully otherwise can head to food poisoning .
Radiation
Radiation of various frequencies ranging from low-frequency microwaves to high-frequency gamma rays are used to preserve various foods .
- Ultraviolet irradiation- effective in killing bacteria and viruses can be used for surface sterilization of food
- Microwave –heat food by penetrating it
Advantages
- No significant changes develop in sensory characteristics.
- No harmful effects if done as per the recommendation of FDA/PFA .
Disadvantages
- Excessive IR can adversely affect nutrients, flavor, and pigments.
- IR in plastic container is at risk of developing off-flavor.
- Blast chillers:- Use of rapidly moving cold air to chill food evenly and rapidly. This may be fitted with temperature probes.
- Danger zone:- The temperature range of 5-63 °C in which microorganisms multiply rapidly in food. At temperatures below 5°C they become dormant, and at temperatures above 63ºC they start getting killed.
- Pasteurization:- A process to destroy the pathogens in milk and extend its shelf life. Two methods: low temperature holding (LTH) method at 62ºC for 30 minutes, and high temperature short time (HTST) method at 72ºC for 15 seconds.
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