Four ways in which food can be preserved are as follows:
1) Pasteurisation: In this method, milk is preserved by heating at 72C for 15 seconds and then cooling it immediately.
2) Refrigeration: In this method, food items are preserved at 5C.
3) Freezing: In this method, food items are preserved at -18C.
4) Sun drying: In this method, food items like vegetables are dried under the Sun to remove the moisture content from them.