Lactic Acid
Lactic acid is an organic acid typically derived from sugar through a process known asfermentation. This is a process in which microorganisms convert carbohydrates, like sugar, into alcohol and then an acid. Lactic acid is commonly found in foods that have fermented.
The compound was first identified by an eighteenth century Swedish chemist named Carl Wilhelm Scheele. In the following century, French chemist and microbiologist Louis Pasteur discovered that lactic acid was turning the vintage burgundy wine of France sour. During the process of making wine using yeast to ferment grape sugar into alcohol, bacteria had contaminated the mixture and through fermentation converted the sugar to lactic acid rather than alcohol
Since 1850, with the work of French physiologist Claude Bernard, it was known that the human liver stored a sugar called glycogen, and that this sugar was present in human muscle tissue ready to be converted to glucose and metabolized for energy. It was also known that when a muscle is active it accumulates lactic acid. Otto Meyerhof put these two observations together and in a series of experiments found that there was a relationship between the amount of glycogen that disappeared from muscle tissue and the amount of lactic acid that was produced. He proposed that glycogen, when broken down, served as a source of energy in the muscle and that when the supply of oxygen could not keep up with the demand, lactic acid was produced. The effect of lactic acid build up is muscle fatigue. Meyerhof further showed that when the muscle rested and oxygen intake increased, some of the lactic acid combined with oxygen to produce glycogen again. For this work Meyerhof received the 1922 Nobel Prize in physiology or medicine. The series of enzymatic reactions that cause the conversion of glycogen to lactic acid is known as the Embden-Meyerhof pathway.
The work of Meyerhof and his associates paved the way for another pair of Nobel Prize winners, Carl and Gerty Cori. Through a careful series of experiments, the Coris showed the exact metabolic pathway in the conversion from glycogen to lactic acid and discovered the role of each intermediary compound as well as the high-energy phosphate molecules which store and transfer energy. For their work on the conversion of glycogen they received the 1947 Nobel prize which they shared with an Argentine physiologist, Bernardo Houssay.
Six years later the Nobel Prize in physiology or medicine went to Hans Krebs and Fritz Lipmann who worked on the remaining steps that convert lactic acid into carbon dioxide and water. An entire series of biochemical reactions break down sugar completely into carbon dioxide and water with the release of energy used by cells. A repeating portion of the intermediary reactions in which citric acid is converted to oxaloacetic acid is known as the citric acid cycle or the Krebs cycle, named for its discoverer.
Lactic acid has many uses. It is used in the manufacture of foods and beverages such as cheeses, confectionery, and soda. It is also used in the production of leather hides. Additionally, it is used in the manufacture of cosmetics, toiletries, household products, an medicines.
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