Explain physical methods for preservation of food.

Explanation

(1) By removal of heat (By cooling) : This method involves refrigeration, freezing preservation, dehydrofreezing, preservation or carbonation.
Cooling leads to lowering of temperature which prevents the growth of micro-organisms. Example : Fresh fruits, vegetables are preserved by this method.
(2) By addition of heat : It involves pasteurization or sterilization. It is also called canning or heat processing.
Solid and liquid foods are preserved by this method on a large scale as heating kills the micro-organisms. Example : Milk is pasteurized for its preservation.
(3) By removal of water (Dehydration) : Water is removed by sun-drying, low temperature evaporation, freeze drying or puff drying.
As water is removed, the growth of micro-organisms is prohibited.
Example : Various vegetables, fruits and foodgrains are preserved by this method.
(4) By irradiation : UV or ionizing radiation is used to preserve .The irradiation controls the growth of micro-organisms. High mergy electromagnetic radiation produces desired effects without inducing radioactivity in food.
Example : Bakery products are preserved by irradiation.