Describe the principle on which the …

The food materials like milk, fruits, vegetables, meat, fish, cooked food, etc. get spoiled easily as they contain a lot of water due to which microorganisms can grow on them easily. We can prevent such food items by the proper methods of food preservation. The process in which the food materials are given a suitable physical or chemical treatment to prevent their spoilage is called food preservation. The various methods of food preservation are:

1. Sun drying – Drying (dehydration) means removal of water from food materials which are to be preserved. In the absence of moisture, the food does not get spoiled because the microorganisms which spoil the food do not grow in dry conditions. The vegetables like spinach, methi leaves, peas and cauliflower are preserved by sun drying method.
2. Heat and Cold Treatments – Heat kills many microorganisms and prevents the food from spoilage. Example – boiling of milk to prevent its spoilage. Pasteurised milk can be consumed without boiling as it is free from harmful microbes. During pasteurisation, milk is heated to about 70^oC for 15 to 30 seconds and then suddenly chilled and stored.
3. Storage and Packing – Now-a-days, dry fruits and even vegetables are sold in sealed, air-tight packets to prevent the attack of microorganisms on them.