Principle of Food Preservation

Food preservation can be defined as the science which deals with the methods of prevention of decay or spoilage of food, thus allowing it to be stored in a fit condition for future use. It is better if the following directions are kept in mind to control the spoilage.

1.      Raw materials should be thoroughly examined and handled hygienic conditions to avoid microbial spoilage.

2.      Equipments must be cleaned every time before use.

3.      The cans should be carefully filled and exhausted sufficiently to produce a good vacuum.

4.       Processing should take place as soon as possible after sealing of cans or bottles. The cooling process should also be done in such a manner that the cans are left sufficiently warm to dry off surplus moisture but not hot enough to cause "stack" burning.

5.      Use of contaminated water should be avoided.

6.      The finished products after canning or bottling should be stored in well- ventilated rooms in a cool and dry place. High storage temperature should be avoided.

Freshly prepared products are highly attractive in appearance and possess good taste and aroma, but deteriorate rapidly if kept for some time. This is on account of several reasons such as. fermentation caused by moulds, yeasts and bacteria, enzymes present in the product may affect the colour and flavour adversely, e.g. apple juice turns brown due to the activity of oxidative enzymes in it, chemicals present in the pulp/juice may react with one another and spoil its taste and aroma, air coming in contact with the product, may react with the glucosidal materials present in it and render the product bitter, e.g., Navel orange and sweet lime juices often turn bitter when they are exposed to air even for a short time. and traces of metal from the equipment may get into the product and spoil its taste and aroma. In the preservation of foods by various methods, the following principles are involved:

1. Prevention or delay of microbial decomposition

a)      by keeping out microorganisms (asepsis)- Nature provides protective coverings around the food in the form of shells of nuts, die skins of fruits and vegetables, the shells of eggs, and the skin or fat on meat or fish. These protective coverings act as a preservative factor, thereby preventing or delaying microbial decomposition. Even in the food industry several aseptic methods are adopted to prevent the contamination of foods during its processing. Like canning. Packaging of foods is also an application of asepsis.

b)      by removal of microorganisms, e.g., by filtration-Filtration is a method used for the complete removal of micro­organisms and is successfully applied only to clear liquids such as water, fruit juices, beer, soft drinks and wine. This filter is sterilised and made “bacteria proof” before being used as a filtration device.

c)      by hindering the growth and activity of microorganisms, e.g., by low temperature, drying, anaerobic conditions, chemicals or antibiotics- This may be done by low temperature or drying or by providing anaerobic conditions. This principle is used as a preservative factor in canned and packaged foods. Low temperature at which foods are preserved in cold storage slows down and sometimes prevents bacterial activity. Drying of foods is a very effective method of avoiding spoilage of food, since micro-organisms cannot flourish in the absence of moisture. Certain chemicalslike sodium benzoate and potassium metabi­sulphite may be used for preservation, but they should be used with great care as an excess of any of them may result in poisoning.

d)      by killing the microorganisms, e.g., by heat or radiation- In this process gamma rays or high speed electrons are used to destroy the micro-organisms. Both types of radiations are termed as ionized radiations. This topic will be dealt with in detail under “Methods of Food Preservation”.

2. Prevention or delay of self-decomposition of the food

a)      by destruction or inactivation of enzymes, e.g., by blanching;-

b)      by prevention or delay of chemical reactions, e.g., prevention of oxidation by means of means of an antioxidant.

This is done by destruction or inactivation of food enzymes by blanching. The inactivation affects many plant enzymes which otherwise might cause toughness and change in colour. All plant and animal tissues contain enzymes which are highly active at room temperature and above. Blanch­ing is done with hot water or steam and the extent of treatment applied varies with the kind of food being treated. The brief heat treatment is supposed to accomplish reduction of the number of micro-organisms on the food, enhancement of the green colour of vegetables such as peas and spinach, and prevention of damage because of mechanical causes, insects and animals.

3. Prevention of damage by insects, animals, mechanical causes, etc.

To retain the natural taste and aroma of a product, it is necessary to preserve it soon after preparation, without allowing it to stand for any length of time. Various methods of preservation are employed and each has its own merits. Items of food can be damaged either by insects and animals or by mishandling. The entire operation of preserving foods is divided into three stages of careful handling:

                                            I.                        Proper packaging

                                         II.                        Quick and effective transportation

                                       III.                        Providing good storage facilities, like silos for grains and cold storages for fruits

and vegetables