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Malic acid

A dicarboxylic acid produced by a living organism, with a chemical formula: C4H6O5
Malic acid is an organic compound synthesized by a living organism. It is a dicarboxylic acid, i.e. a compound containing two carboxyl functional groups (-COOH). It is colourless and odorless. It has two stereoisomeric forms: L-Malic acid and D-Malic acid. The L-malic acid though is the only naturally occurring form whereas the other isomeric form is produced artificially. In living organisms, malic acid is an essential biochemical compound. Its ester, malate, is involved in Krebs cycle. Krebs cycle (or citric acid cycle) is a series of redox reactions that occur in the mitochondrion to ultimately generate chemical energy that fuel metabolic reactions. In Krebs cycle, malate is produced during the hydration of C-C double bond of fumarate with H2O. The malate produced then acts as the substrate that reacts with NAD+ to produce oxaloacetate, NADH and hydrogen anion.
Malic acid was first described in 1785 by Sheele who was able to isolate it from unripe apples. The name malic is derived from the Latin malum, meaning apple. Apart from apple, malic acid is also found in other frutis, e.g. grapes, watermelons, and cherries.1
Commercially, malic acid is marketed as food additive such as in beverages and candies. It is also used for metal cleaning and finishing, electroless plating, infusions, paints, and pharmaceuticals. 1
IUPAC name: Hydroxybutanedioic acid
Chemical formula: C4H6O5
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1 Schaechter, M. (2009). Encyclopedia of Microbiology. Academic Press. p.428.

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