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|Section2= |Section4= |Section8= |Section6= |Section7= }} Lactic acid is an organic compound with the formula CH3CH(OH)CO2H. It is a white, water-soluble solid or clear liquid that is produced both naturally and synthetically. With a hydroxyl group adjacent to the carboxyl group, lactic acid is classified as an alpha hydroxy acid (AHA). In the form of its conjugate base called lactate, it plays a role in several biochemical processes. In solution, it can ionize a proton from the carboxyl group, producing the lactate ion CH3CH(OH)CO2−. Compared to acetic acid, its pKa is 1 unit less, meaning lactic acid deprotonates ten times more easily than acetic acid does. This higher acidity is the consequence of the intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group. Lactic acid is chiral, consisting of two optical isomers. One is known as L-(+)-lactic acid or (''S'')-lactic acid and the other, its mirror image, is D-(−)-lactic acid or (''R'')-lactic acid. A mixture of the two in equal amounts is called DL-lactic acid. Lactic acid is hygroscopic. DL-lactic acid is miscible with water and with ethanol above its melting point which is around 17 or 18 °C. D-lactic acid and L-lactic acid have a higher melting point. In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal, which is governed by a number of factors, including monocarboxylate transporters, concentration and isoform of LDH, and oxidative capacity of tissues. The concentration of blood lactate is usually at rest, but can rise to over 20 mmol/L during intense exertion〔(【引用サイトリンク】 title=Lactate Profile )〕 and as high as 25 mmol/L afterward. In industry, lactic acid fermentation is performed by lactic acid bacteria, which convert simple carbohydrates such as glucose, sucrose, or galactose to lactic acid. These bacteria can also grow in the mouth; the acid they produce is responsible for the tooth decay known as caries. In medicine, lactate is one of the main components of lactated Ringer's solution and Hartmann's solution. These intravenous fluids consist of sodium and potassium cations along with lactate and chloride anions in solution with distilled water, generally in concentrations isotonic with human blood. It is most commonly used for fluid resuscitation after blood loss due to trauma, surgery, or burn injury. ==History== Lactic acid was refined for the first time by the Swedish chemist Carl Wilhelm Scheele in 1780 from sour milk. The name reflects the ''lact-'' combining form derived from the Latin word for milk. In 1808, Jöns Jacob Berzelius discovered that lactic acid (actually L-lactate) also is produced in muscles during exertion. Its structure was established by Johannes Wislicenus in 1873. In 1856, Louis Pasteur discovered ''Lactobacillus'' and its role in the making of lactic acid. Lactic acid started to be produced commercially by the German pharmacy Boehringer Ingelheim in 1895. In 2006, global production of lactic acid reached 275,000 tonnes with an average annual growth of 10%.〔(NNFCC Renewable Chemicals Factsheet: Lactic Acid )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「lactic acid」の詳細全文を読む スポンサード リンク
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