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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