Notes on the essential Principles of food Preservation

All methods of food preservation are based on the following principles:

I. Prevention or delay of microbial decomposition

This is brought about by four different ways as discussed below:

(i) By keeping out micro-organisms (asepsis):

Many protective coverings both naturally and artificially act as a preservative factor thereby preventing or delaying microbial decomposition. Nature provides protective covering around the food in the form of nuts, the skins of fruits and vegetables, shells of eggs and the skin of fish and meat to avoid decomposition.

Commercially, even in food industry several ascetic methods are adopted to prevent the contamination of foods during its processing as in canning industry and dairy industry. Also, packing of foods from simple wrappers to polythene bags, moisture-proof wrappings and hermetically sealed containers are also an application of asepsis.

(ii) By removal of micro-organisms:

In this method, filtration is used for the complete removal of micro-organisms by forcing the liquid through the filter under pressure to water, fruit juices, beer, soft drinks and wine.

(iii) By hindering the growth the activity of micro-organisms:

This may be done by low temperature or drying and in anaerobic conditions.

In anaerobic (absence of oxygen) conditions as in canned and packaged foods, some aerobic organisms are destroyed. While those who survive are unable to multiply in the absence of oxygen.

Similarly, drying of foods as with milk is a very effective method of avoiding food spoilage as the micro organisms.

Even with the use of certain chemicals like sodium benzoate and potassium metabisulphate, foods could be preserved for a long time.

(iv) By killing the microorganisms using heat or radiation:

In this process, gamma rays or high speed electrons termed as ionized radiations are used to destroy the micro organisms.

II. Prevention or delay of self decomposition of food

(i) By destruction or inactivation of food enzymes, i.e., by blanching or boiling. This can be carried out either by dipping the vegetables in hot water or by exposing them to steam for a few minutes. Heating milk is another example, where the heat inactivates the enzymes present in the milk and extends its shelf life.

(ii) By prevention or delay of purely chemical reactions food like fats and oils can turn rancid and become unfit to eat because of oxidation. This can be prevented by addition of small quantities of chemicals called ‘anti-oxidants’ which prevents the oxidation of fats.

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

Foods can be damaged either by insects and animals or by mishandling. Therefore, utmost care has to be taken in packaging, transportation and providing good storage facilities especially for fruits and vegetables.