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Food storage: A pre-requisite to food security
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Saturday, 16 April, 2005, 08 : 00 AM [IST]
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Mumbai
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Preservation or storage of food items is a pre-requisite for food security. The seasonal nature of production and the long and unmanageable distances between the production and consumption centres and the rising gap between demand and supply have posed great challenges to conventional techniques of food preservation and thereby to food security.
India has been practising various methods of food preservation from time immemorial such as sun drying, pickling and fermentation. These methods were to be supplemented with more energy consuming techniques like refrigeration, freezing and canning. These methods however had its merits and demerits. The quest was ever on for newer methods of food preservation with least change in sensory qualities.
Challenges in Food Processing
Unprocessed foods are susceptible to spoilage by biochemical processes, microbial attack and infestation. The right post harvest practices such as good processing techniques, and proper packaging, transportation and storage (of even processed foods) can play a significant role in reducing spoilage and extending shelf life. The challenges in processing lie in retaining the nutritional value, flavour, aroma, and texture of foods, and presenting them in near natural form with added conveniences. However, such qualities cannot be readily quantified and correlated with physico-chemical parameters, sensory evaluations providing the only means of benchmarking. Besides, processed foods need to be offered to the consumer in hygienic and attractive packaging, and at low incremental costs.
The challenges for the food preservation, distribution and processing sectors are diverse and demanding, and need to be addressed on several fronts to derive maximum market benefits. Presently, the organizations addressing the educational and R & D requirements are too few, and there is a pressing need for supplementing their efforts. In the emerging scenario, the Food Engineering professional needs to develop sufficient awareness and appreciation of the relevant principles of life sciences, and physical sciences, as well as of a wide variety of other topics including: nutrition, preservation and storage techniques, processing unit operations, bio-processing, waste management, distribution and supply chain management, food laws and regulations and so on. Besides, the professional needs
to develop an appreciation of R&D and innovation in critical technology areas such as: newer or novel process development in preservation and storage techniques, rheology, colloids and dispersal systems, packaging-polymers and composites, sensors for detection and process control, bioprocess engineering, and so on.
The latest methods in food preservation that have suited industry needs include radiation, dehydration, refrigeration, canning, pasteurization, deep-freezing etc. While each has its own set of advantages, it is the Radiation method that is the most widely followed method in India. Radiation of food items involves treating certain types of food with ionising energy or radiation. It is used to destroy bacteria and parasites that cause human illnesses. It can also make food last longer by destroying or inactivating insects, moulds, yeasts etc. that spoil food and delay ripening of fruits and vegetables besides limiting unwanted sprouting of potatoes and similar vegetables.
Radiation Processing
Radiation technique makes the food safer to eat by destroying bacteria, which is very much similar to the process of pasteurization. In effect, radiation disrupts the biological processes that lead to decay and the ability to sprout. Being a cold process, radiation can be used to pasteurize and sterilize foods without causing changes in freshness and texture of food unlike heat. Further, unlike chemical fumigants, radiation does not leave any harmful toxic residues in food and is more effective and can be used to treat packaged commodities too.
Over 42 countries in the world including USA, UK, Canada and France have given clearance for radiation processing of food. The Government of India has permitted the use of radiation technology in preservation of food items such as potato, onion, rice samolina (sooji or rawa) wheat flour or maida, mango, raisins, dried dates, ginger, garlic, shallots (small onions) as well as meat and meat products including chicken.
Dehydration
Preservation of foods by drying is one of the earliest and simplest techniques used for centuries. Dehydration is the process by which surplus water is removed with out drastically reducing the taste and nutritive value of the foods. Foods such as meat, fish, figs, apples, raisins, apricots, gooseberries, herbs, and vegetables are generally preserved by this method. They keep well because of the combination of the physical changes. In fruits as the moisture is removed the concentration of sugar goes up and this increased sugar concentration adds to the unfavourable conditions for bacterial growth.
The principle of dehydration is that bacteria are unable to survive in the absence of moisture.
Dried foods can be transported easily due to its lightweight and volume. In this method vitamin C and beta-carotene are lost mainly but the sugar and fibre concentrates. This method also causes severe loss of taste, aroma, texture etc.
Refrigeration
Refrigeration works on the principle that bacterial and enzymatic activities are minimal at low temperatures. Foods should be placed in the refrigerator as quickly as possible and it should be covered. This will also prevent foods from acquiring the flavour of the other foods.
Whole fruits and vegetables can be wrapped in brown paper or newspaper to keep fresh for a longer period. Hot foods must be allowed to cool to room temperature before they are placed in the refrigerator. Top shelves maintain a lower temperature than the bottom ones so easily perishable foods such as milk must be kept in the upper shelves where as curd, vegetables, fermented batters can be placed in the lower shelves. If cooked foods have been lying at room temperature for a long time they should be heated again and cooled at room temperature before they are placed in refrigerator. When vegetables are brought in bulk they take up a lot of space in the refrigerator for short-term preservation. The vegetables can be cleaned and cut and kept in closed containers. Tomatoes can be blanched, crushed boiled a little and packed in bottles and can be stored. Prepared food such as sambhar and curries can also be stored in airtight containers for a week. Nutrients in general are retained well. There will be small reduction in the water-soluble vitamin and mineral content of vegetables and fruits, which are blanched before refrigerated or frozen. Each food has a recommended maximum storage time beyond which it slowly begins to
deteriorate. Cold prevents the growth and multiplication of bacteria
With the advancement of technology more efficient refrigeration techniques have been developed. This has led to freezing techniques such as air blast freezing, contact freezing etc. The latest and most advanced method of refrigeration is the cryogenic method of refrigeration or the refrigeration using liquid nitrogen at extremely low temperatures. Currently liquid nitrogen is extensively used in the food industry.
Use of Chemical Preserves
This is most used and abused method of food preservation. Chemical preservatives serve as either anti-microbial, antioxidant or both. It also minimises the damage to some essential amino
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