Explain physical methods for preservation of food.

Explanation

(i) By removal of heat (By cooling) : Refrigeration, freezing preservation, dehydrofreezing , preservation or carbonation such processes are involved in this method .
Cooling leads to lowering of temperature which prevents the growth of micro - organisms
Example : Fresh fruit , vegetables are preserved by this method .
(ii) By addition of heat : It involves methods like pasteurization or sterilization , it also called as camnning or heat processing .
By this method solid liquid foods are preserved on a large scale , as heating kills the microorganisms .
Example : Milk is pasteurized for its preservation .
(iii) By removal of water (Dehydration ) : In this method , water is removed by sun - drying , low temperature evaporation , freeze drying or puff drying .
The growth of micro - organisms is prohibited as all the water is removed .
Example : Various vegetables , fruit and foodgrains are preserved by this method
(iv) By irradiation : UV or ionzing radiation is used to preserve food . The irradiation controls the growth of microorganisms . High energy eletro magnetic radiation produces desired effects without inducing radioactivity in food .
Example : Bakery products are preserved by irradiation .