Auto preservatives: Sonic substances produced in the food act as auto preservative for that substance. For example lactic acid & ethanol arc such type of auto preservative. Lactic acid produced in the milk and ethanols produced as in sugar are act as auto preservatives.
Lactic acid reduced the pH value and protects the foods from microorganism and ethanol act as antiseptic, because microorganism cannot tolerate high concentrated ethanol.
