The word 'malic' is derived fromLatinmālum, meaning'apple'. The related Latin wordmālus, meaning'apple tree',[citation needed] is used as the name of the genusMalus, which includes all apples and crabapples;[5] and is the origin of othertaxonomic classifications such asMaloideae,Malinae, andMaleae.
Malate is also synthesized by thecarboxylation ofphosphoenolpyruvate in the guard cells of plant leaves. Malate, as a double anion, often accompanies potassium cations during the uptake of solutes into the guard cells in order to maintain electrical balance in the cell. The accumulation of these solutes within the guard cell decreases thesolute potential, allowing water to enter the cell and promote aperture of the stomata.
Malic acid was first isolated fromapple juice byCarl Wilhelm Scheele in 1785.[6]Antoine Lavoisier in 1787 proposed the nameacide malique, which is derived from theLatin word for apple,mālum—as is itsgenus nameMalus.[7][8]In German it is namedÄpfelsäure (orApfelsäure) after plural or singular of a sour thing from the apple fruit, but the salt(s) are calledMalat(e).Malic acid is the main acid in many fruits, includingapricots,blackberries,blueberries,cherries,grapes,mirabelles,peaches,pears,plums, andquince,[9] and is present in lower concentrations in other fruits, such ascitrus. It contributes to the sourness of unripe apples. Sour apples contain high proportions of the acid. It is present ingrapes and in most wines with concentrations sometimes as high as 5 g/L.[10] It confers a tart taste towine; the amount decreases with increasing fruitripeness. The taste of malic acid is very clear and pure inrhubarb, a plant for which it is the primary flavor. It is also the compound responsible for the tart flavor ofsumac spice. It is also a component of some artificialvinegar flavors, such as "salt and vinegar" flavored potato chips.[11]
The process ofmalolactic fermentation converts malic acid to much milderlactic acid. Malic acid occurs naturally in all fruits and many vegetables, and is generated in fruit metabolism.[12]
Malic acid, when added to food products, is denoted byE number E296. It is sometimes used with or in place of the less sourcitric acid in sour sweets. These sweets are sometimes labeled with a warning stating that excessive consumption can cause irritation of the mouth. It is approved for use as afood additive in the EU,[13] US[14] and Australia and New Zealand[15] (where it is listed by itsINS number 296).
Malic acid contains 10 kJ (2.39 kilocalories) of energy per gram.[16]
Racemic malic acid is produced industrially by the double hydration ofmaleic anhydride. In 2000, American production capacity was 5,000 tons per year. Theenantiomers may be separated bychiral resolution of the racemic mixture.S-Malic acid is obtained by fermentation offumaric acid.[17]
Carbon monoxide and water are liberated during this reaction.
Malic acid was important in the discovery of theWalden inversion and theWalden cycle, in which (−)-malic acid first is converted into (+)-chlorosuccinic acid by action ofphosphorus pentachloride. Wetsilver oxide then converts the chlorine compound to (+)-malic acid, which then reacts with PCl5 to the (−)-chlorosuccinic acid. The cycle is completed when silver oxide takes this compound back to (−)-malic acid.
^Silva, Andre M. N.; Kong, Xiaole; Hider, Robert C. (2009). "Determination of the pKa value of the hydroxyl group in the α-hydroxycarboxylates citrate, malate and lactate by 13C NMR: implications for metal coordination in biological systems".BioMetals.22 (5):771–778.doi:10.1007/s10534-009-9224-5.ISSN0966-0844.PMID19288211.
^Carl Wilhelm Scheele (1785)"Om Frukt- och Bår-syran" (On fruit and berry acid),Kongliga Vetenskaps Academiens Nya Handlingar (New Proceedings of the Royal Academy of Science),6 : 17-27. From page 21:" ... vil jag hådanefter kalla denÅple-syran." ( ... I will henceforth call itapple acid.)
^de Morveau, Lavoisier, Bertholet, and de Fourcroy,Méthode de Nomenclature Chimique (Paris, France: Cuchet, 1787),p. 108.
