Food preservation is the process of prevention of food from decay or spoilage, by storing in a condition fit for future use. Food is preserved to
✓increase the shelf life of food
✓retain the colour, texture, flavour and nutritive value
✓increase food supply
✓decrease wastage of food
Methods of Food Preservation
The various method of food preservation are explained below.
Drying is the process of preservation of food by 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 microorganisms such as bacteria, yeasts and moulds.
In this process, food products like meat and fish are exposed to smoke. The drying action of the smoke tends to preserve the food.
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.
It is a process of storing the perishable foods such as vegetables, fruits and fruit products, milk and milk products etc. at low temperature. Preserving the food products at low temperature slows down the biological and chemical reactions and prevents its spoilage.
Freezing is one of the widely used methods of food preservation. This process involves storing the below 0°C at which microorganisms cannot grow, chemical reactions are reduced and metabolic reactions are also delayed.
Pasteurization is a process of heat treatment of liquid food products. e.g. For preservation of milk and beverages. This process also 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.
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.
Addition of Preservatives
Food can be preserved by adding natural and synthetic preservatives.
Some naturally available materials like salt, sugar and oil are used as food preservatives.
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, fish, gooseberry, lemon and raw mangoes are preserved by salting. Salt is also used as a preservative in pickles, canned foods etc.
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.
Addition of oil
Addition of oil in pickles prevents the contact of air with food. Hence microorganisms cannot grow and spoil the food.
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.