Malic acid

Malic acid is a organic compound that is found in many fruits and vegetables, most notably apples. It is a dicarboxylic acid that is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used in food preparation and beverages for its sour taste.

Chemistry

Malic acid has two stereoisomeric forms (L- and D-enantiomers), though only the L-isomer exists naturally. The salts and esters of malic acid are known as malates. The malate anion is an intermediate in the citric acid cycle.

Biosynthesis

L-Malic acid is the naturally occurring form, whereas a mixture of L- and D-malic acid is produced synthetically. L-Malic acid is synthesized in the cytosol of plant cells by the enzyme malate dehydrogenase, a part of the oxidative decarboxylation process.

Uses

Malic acid contributes to the sourness of green apples. It is present in grapes and in most wines with concentrations sometimes as high as 5 g/l. It confers a tart taste to wine, although the amount decreases with increasing fruit ripeness. The process of malolactic fermentation converts malic acid to much milder lactic acid.

Safety

Malic acid, when added to food products, is denoted by E number E296. Malic acid is the source of extreme tartness in United States confectionery, the so-called extreme candy. It is also used with or in place of the less sour citric acid in sour sweets. These sweets are sometimes labeled with a warning that excessive consumption can cause irritation of the mouth. It is approved for use in the EU, US and Australia and New Zealand.

See also

• Citric acid
• Tartaric acid
• Fumaric acid

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  Malic acid structure

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  L-Malic acid structure

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  D-Malic acid structure