Methods of Food Preservation

Methods of Food Preservation

1. Dehydration/ Drying

Drying or dehydration is the process of removal of water/moisture content in the food. It can be done either by sun-drying, (e.g. cereals, fish) or vacuum drying (e.g. milk powder, cheese powder) or hot air drying (e.g. grapes, dry fruits, potato flakes). Drying inhibits the growth of microorganism such as bacteria, yeasts and moulds.

2. Smoking

In this process, food products like meat and fish are exposed to smoke. The drying action of the smoke tends to preserve the food.

3. Irradiation

Food irradiation is the process of exposing food to optimum levels of ionizing

radiations like x-rays, gamma rays or UV rays to kill harmful bacteria and pests and to preserve its freshness. is process is sometimes called ‘cold pasteurization’ as the product is not heated. Irradiation does not destroy the taste or nutritive value of food. The shelf life of onions and potatoes increases when exposed to radiation.

4. Use of inert gas

Nitrogen gas is filled in air-tight packets of potato wafers and other food products thus preventing the growth of fungus and insects in them.

5. Cold storage

The process of storing the perishable foods such as vegetables, fruits and fruit products, milk and milk products etc. at low temperature in a refrigerator is called cold storage. Preserving the food at low temperature slows down the biological and chemical reactions in food products and prevents its spoilage.

6. Freezing

Freezing is one of the widely used methods of food preservation. This process involves storing the food below 00C at which microorganisms cannot grow, chemical reactions are reduced and metabolic reactions are also delayed.

7. Pasteurization

Pasteurization is a process of food preservation, which is named after the scientist Louis Pasteur. This process involves boiling of milk to a temperature of 63°C for about 30 minutes and suddenly cooling to destroy the microbes present in the milk. Pasteurisation helps in avoiding spoilage of milk.

Simple representation of the process of pasteurisation of milk

8. Canning

In this method of food preservation, most vegetables, fruits, meat and dairy

products, fruit juices and some ready-to -eat foods are processed and stored in a clean, steamed air tight containers under pressure and then sealed. It is then subjected to high temperature and cooled to destroy all microbes.

9. Addition of preservatives

Food can be preserved by adding natural and synthetic preservatives.

A) Natural preservatives

Some naturally available materials like salt, sugar and oil are used as food preservatives.

1.     Addition of salt: It is one of the oldest methods of preserving food. Addition of salt removes the moisture content in the food by the process of osmosis. This prevents the growth of bacteria and reduces the activity of microbial enzymes. Meat, sh, gooseberry, lemon and raw mangoes are preserved by salting. Salt is also used as a preservative in pickles, canned foods etc.

2.     Addition of sugar: Sugar/Honey is added as a preservative to increase the shelf life of fruits and fruit products like jams, jellies, squash, etc. The hygroscopic nature of sugar/ honey helps in reducing the water content of food and also minimizing the process of oxidation in fruits.

3.     Addition of oil: Addition of oil in pickles prevents the contact of air with food. Hence microorganisms cannot grow and spoil the food.

B. Synthetic preservatives

Synthetic food preservatives like sodium benzoate, citric acid, vinegar, sodium meta bisulphate and potassium bisulphate are added to food products like sauces, jams, jellies, packed foods and ready- to-eat foods. These preservatives delay the microbial growth and keep the food safe for long duration.