Methods of food preservation would help to prevent a large amount of food being wasted. Some of the preservation methods not only reduce the nutritive value of foods but causes harmful effect directly.
Preservative methods vary according to the food items and quantity of the items to be preserved. There are household and commercial methods of food preservation available. The principles of food preservation can be broadly classified into two types. They are -
Bactericidal method: In these methods most of the micro-organisms are killed. Examples of bactericidal methods of preservations are cooking, canning, pasteurisation, sterilisation, irradiation etc.
Bacteriostatic method: The principle of this method is prevention of multiplication of micro-organisms. This may be achieved by removal of water, use of acids, oil, or spices and by keeping in low temperature. The commonly used methods of this principle are drying, freezing, pickling, salting, and smoking. A layer of oil on the top of any food prevents growth of micro-organisms such as moulds and yeast's by preventing exposure to air. Spices like pepper and turmeric have little bacteriostatic effect.
Main food preservation methods
Method Effect on microbial growth or survival
Refrigeration or chilling Low temperature to retard growth
Freezing Low temperature and reduction of water activity to prevent growth
Drying, curing and conserving Reduction in water activity sufficient to delay or prevent growth
Vacuum and oxygen free modified atmosphere packaging Low oxygen tension in inhibit strict aerobes and delay growth of facultive anaerobes
Carbon dioxide enriched modified atmosphere packaging Specific inhibition of some micro-organisms by carbon dioxide
Addition of acids Reduction of pH value and sometimes additional inhibition by the particular acid
Lactic fermentation Reduction of pH value in situ by microbial action and sometimes additional inhibition by the lactic and acetic...