monosodium glutamate

White, crystalline powder, the sodium salt of glutamic acid (an amino acid found in proteins that plays a role in the metabolism of plants and animals). It has been shown to possess its own taste receptor, making it the fifth taste (see umami), alongside sweet, sour, acid, and salt. It is used to enhance the flavour of many packaged and ‘fast foods’, and in Chinese cooking. Ill effects may arise from its overconsumption, and some people are very sensitive to it, even in small amounts. It is commercially derived from vegetable protein. It occurs naturally in soybeans and seaweed.