Lactic Acid (redirected from 2-hydroxypropanoic acid)

lactic acid, CH₃CHOHCO₂H, a colorless liquid organic acid. It is miscible with water or ethanol. Lactic acid is a fermentation product of lactose (milk sugar); it is present in sour milk, koumiss, leban, yogurt, and cottage cheese. The protein in milk is coagulated (curdled) by lactic acid. Lactic acid is produced in the muscles during intense activity. Calcium lactate, a soluble lactic acid salt, is used as a source of calcium in the diet. Lactic acid is produced commercially for use in pharmaceuticals and foods, in leather tanning and textile dyeing, and in making plastics, solvents, inks, and lacquers. Although it can be prepared by chemical synthesis, production of lactic acid by fermentation of glucose and other substances is a less expensive method. Chemically, lactic acid occurs as two optical isomers, a dextro and a levo form; only the levo form takes part in animal metabolism. The lactic acid of commerce is usually an optically inactive racemic mixture of the two isomers.

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lactic acid

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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lactic acid

a colourless syrupy carboxylic acid found in sour milk and many fruits and used as a preservative (E270) for foodstuffs, such as soft margarine, and for making pharmaceuticals and adhesives. Formula: CH₃CH(OH)COOH

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lactic acid [′lak·tik ′as·əd]

(biochemistry)

C₃H₆O₃A hygroscopic α-hydroxy acid, occurring in three optically isomeric forms:Lform, in blood and muscle tissue as a product of glucose and glycogen metabolism;Dform, obtained by fermentation of sucrose; andDLform, a racemic mixture present in foods prepared by bacterial fermentation, and also made synthetically.

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Lactic Acid 

(α-hydroxypropionic acid, CH₃CH(OH)-COOH), a monobasic hydroxycarboxylic acid; an important intermediate metabolite in animals, plants, and microorganisms.

Lactic acid occurs as colorless water-soluble crystals. It exists in two optically active forms, (−) and (+), with a melting point of 25°–26°C, and in an inactive racemic form, (±), with a melting point of 18°C. The (−) and (+) lactic acids undergo racemization at 130°–150°C and produce salts (lactates) and esters similar to carboxylic acids.

Lactic acid is formed during the fermentation of sugary substances by various species of lactic acid bacteria (for example, during the souring of milk, the pickling of cabbage and vegetables, the aging of cheese, and ensilage). Either a racemate or one of the optically active forms of lactic acid is produced, depending on the species of bacteria and the type of sugar present. The industrial fermentation of cane sugar, dextrose, and maltose by Bacillus Delbrucki yields (±) lactic acid, which is used to delime leather in tanning and for chromate reduction in mordanting chrome. Lactic acid salts are used as mordants in dyeing and printing, and lactic acid esters as varnish thinners.

In animal tissue (primarily muscle), the formation of (+) lactic acid is the final stage in the anaerobic enzymic breakdown of carbohydrates, or glycolysis. In the absence of O₂, the amount of lactic acid produced in muscle tissue equals the amount of glycogen lost. (Muscle fatigue is associated with the depletion of glycogen reserves and the accumulation of lactic acid.) In the presence of O₂, approximately 20 percent of the lactic acid is oxidized to CO₂ and H₂O, the energy released is used to convert the remaining lactic acid to glycogen, and the onset of fatigue is more gradual. The reversible reduction of pyruvic acid (pyruvate) to lactic acid (lactate) occurs during the final stage of glycolysis upon the action of lactate dehydrogenase. Plants and microorganisms produce lactic acid by pyruvate reduction.

V. N. FROSIN