lactic acid

Biochem.

a colorless or yellowish, syrupy, water-soluble liquid, C₃H₆O₃, produced during muscle contraction as a product of anaerobic glucose metabolism, abundant in sour milk, prepared usually by fermentation of cornstarch, molasses, potatoes, etc., or synthesized: used chiefly in dyeing and textile printing, as a flavoring agent in food, and in medicine.

[1780-90]

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Carboxylic acid found in certain plant juices, in blood and muscle, and in soil.

In blood it occurs in the form of its salts (lactates) when glycogen is broken down in muscle; it can be reconverted to glycogen in the liver. Stiffness and soreness after prolonged heavy exercise are due to accumulated lactic acid in the muscles. The end product of bacterial fermentation, lactic acid is the most common acidic constituent of fermented milk products (e.g., sour milk and cream, cheese, buttermilk, yogurt). It is used in other foods as a flavouring or preservative and industrially in tanning leather and dyeing wool and as a raw material or catalyst in many chemical processes.

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▪ chemical compound

also called  α-hydroxypropionic acid , or  2-hydroxypropanoic acid 

      an organic compound belonging to the family of carboxylic acids, present in certain plant juices, in the blood and muscles of animals, and in the soil. It is the commonest acidic constituent of fermented milk products such as sour milk, cheese, and buttermilk.

      First isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele (Scheele, Carl Wilhelm), lactic acid is manufactured by the fermentation of molasses, starch, or whey in the presence of alkaline substances such as lime or calcium carbonate; it is available as aqueous solutions of various concentrations, usually 22–85 percent, and degrees of purity. Lactic acid is used in tanning leather and dyeing wool; as a flavouring agent and preservative in processed cheese, salad dressings, pickles, and carbonated beverages; and as a raw material or a catalyst in numerous chemical processes. Pure lactic acid, rarely prepared, is a colourless, crystalline substance that melts at 18° C (64° F); it rapidly absorbs moisture from the atmosphere.

      Lactic acid occurs in the blood (in the form of its salts, called lactates) when glycogen is broken down in muscle and can be converted back to glycogen in the liver. Lactates are also the products of fermentation (q.v.) in certain bacteria.

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