Any food item can be kept for certain period of time under normal conditions of temperature and humidity. Food items are fresh, cheap and available in abundance during the seasons. If these are not properly preserved for off seasons consumption, they will get spoiled. Thus, preservation of food items prevents the wastage.
The principles of food preservation are described below:
Use of Low Temperature : It involves storing the food items at a temperature below normal room temperature. The action of micro¬organisms and chemical activity slows down at lower temperatures and as such, the putrefaction or process of decay is delayed and food items can be preserved for periods more than the normal.
Home refrigeration : If can be done by using refrigerator, ice box etc. The perishable food items like fruits, vegetables, fish, meat, egg, milk , curd and leftover food can be preserved for some additional period.
Freezing : The growth of micro-organisms’ enzymatic activity and chemical reactions are extremely slow at a temperature below ice point and the food items can be preserved for weeks together.
Use of High Temperature: Pasteurisation and Canning are examples that utilise high temperature methods for preservation of food. Heating at high temperature destroys all microorganisms and enzymes.
Pasteurization : This generally refers to preserve milk either by holding process or flash process. In holding process, the milk is heated to 65° C and kept at this temperature for 30 minutes and then cooled down. In flash process, the milk is heated to 75° C, only for 15 seconds. This process is also called high temperature for short time (HTST). The milk is cooled and packed in bottles and kept in deep freezer till distribution.
Canning : Vegetables, fruits and meat are preserved by this method. The items are prepared, packed in tins, sealed and then heated to high temperature to destroy the micro-organisms. This process is termed as ‘Sterilisation’. The seal of the tin prevents any contamination of food and thus food is preserved for a long period of time.
Drying : Drying of food items by evaporating the moisture from it prevents the growth of micro-organisms and hence, prevents food from getting spoiled. Drying in sun is very cheap and effective. The vegetables are cleaned, washed, cut and dipped in boiling water for 10 minutes and then sundried.
Use of preservatives : Certain chemicals also prevent the growth of microorganisms. Pickles, jams, murabbas are preserved by using chemicals like salt, vinegar, sugar, spices etc. Sodium benzoate or potassium meta- bisulphite are used as preservatives for squashes, ketchup etc.
Use of radiation : The ultra violet or gamma rays are allowed to pass through packaged food to sterilize it. This is rather a recent technique and not much in use.
