What are the different methods of …

Important methods used for preserving food are :
Chemical Method : Salts and edible are the common chemicals generally used to check the growth of microorganisms. Therefore they are called preservations. We add salt or acid preservatives to pickles to prevent the attack of microbes. Sodium benzoate and sodium metabisulphite are common preservatives. These are also used in the jams and squashes to check their spoilage.
Preservation by Salt : Common salt has been used to preserve meat and fish ages. Meat and fish are covered with dry salt to check the growth of bacteria. Salting is also used to preserve amla, raw mangoes, tamarind etc.
Preservation by sugar : Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content which inhibits the growth of food spoiling bacteria.
Preservation by Oil and Vinegar : Use of oil and vinegar prevents spoilage of pickles because bacteria cannot live in such an environment. Vegetables, fruits, fish and meat are often preserved by this method.