Salt and sugar are widely used for the preservation of fruits and vegetables. The presence of high concentration of salts (15% and 18%) drains out the water from food materials through osmosis and prevents their spoilage by inhibiting bacterial growth. Salt is used both in the dry form as well as in aqueous solution. It is extensively used in the preservation of tamarind, beans, raw mango, amla, fish and meat.
Sugar syrup contains more than 68% sugar. It also inhibits bacterial growth as it has very little free moisture available. The micro-organisms already present in food materials therefore gradually die due to lack of moisture.
Besides salt and sugar, vinegar, oil, species and citric acid are also used as preservatives. These are used in the preparation of pickles, chutney, ketchups and squashes.