Malic acid
- 2 -malic acid
- 2- hydroxybutanedioic
- 2- hydroxybutane -1 ,4 -dioic acid
- Malic acid
- E 296
- 97-67-6 [L- (-) -malic acid ]
- 636-61-3 [D- ( )-malic acid ]
- 6915-15-7 [ DL- (± )-malic acid ]
White powder
Fixed
1.6 g · cm -3
- PKS1 = 3.46
- PKa2 = 5.10
- DL -malic acid: good in water ( 558 g · l-1 at 20 ° C) in ethanol: 455.3 g · l-1
- D-or L -malic acid: well in water ( 363.5 g · l-1 at 20 ° C), in ethanol: 866.0 g · l-1
- Soluble in acetone, slightly soluble in diethyl ether
Risk
1600 mg · kg -1 ( LD50, mouse, oral)
Template: Infobox chemical / molecular formula search available
Malic acid (2 -malic acid, more rarely, malic acid) is a chemical compound of the groups of the dicarboxylic acids and hydroxy carboxylic acids, which occurs as dextrorotatory D and as a left-handed L- malic acid. The L-form is an intermediate in the citric acid cycle. In nature, L -malic acid is mostly in unripe fruits, such as apples, quinces, grapes, barberries, bird berries and gooseberries contain. The esters and salts of malic acid hot Malate (from the Latin malum = apple, not to be confused with maleates, the esters and salts of maleic acid ).
History
L -malic acid was first isolated and described in 1785 by Carl Wilhelm Scheele from apple juice. Antoine Lavoisier in 1787 proposed the name acide Malique, derived from the Latin word for apple, malum ago. Paul Walden could prove the chirality, and the inversion of configuration at the carbon atom by synthesis from L-malic acid and D- malic acid.
Properties
Malic acid has a chiral center and is optically active. Shown below are the left, the L-(- )-malic acid (after CIP convention: (S )-2 -malic acid ) and right D-( )-malic acid (after CIP convention: (R )-2 -malic acid ) in the Fischer projection. The stereocenters are marked with *.
Like all enantiomers have the L-malic acid and D-malic acid, with the exception of the direction of rotation value α, the same physical properties. Such as melting point - - For DL -malic acid, the racemate, the physical properties differ, however, from those of the pure enantiomers of L-malic acid and D -malic acid.
Use
As a food additive (E 296 ), both the L- form and the D-form or racemic mixture may be used. D-malic acid can be converted by enzymes in the human L-malic acid. In practice, their use is rather limited due to the relatively high price. Instead cheaper alternatives, such as citric acid (E 330), sodium benzoate ( E 211 ) or acid (E 338 ) are mostly used. As an additive to potato chips are sodium malate (E 350), potassium malate (E 351) and calcium malate (E 352 ) is used. In medicine, potassium malate is used in hypokalemia as an infusion solution if potassium chloride can not be used because of concurrent hyperchloremia.
Production
The L-malic acid and its salts ( Malate ) are by means of biotechnological processes, catalyzed by the enzyme fumarate hydratase, from fumaric acid (E 297 ) or as a metabolic product of bacteria and fungi (eg, Brevibacterium, Corynebacterium, Escherichia, Microbacterium, Proteus, Pichia ) won. Enantiospecific the addition of water to maleic acid is catalyzed by the maleate hydratase, leading to D-malic acid. Racemic malic acid can be cleaved by the formation of diastereomeric salts with a suitable optically pure amine, L- malic acid and D-malic acid.
Viniculture
L -malic acid is also contained in grapes. A low malic acid content is considered as maturity parameters. When removing the wine can be introduced intentionally or spontaneously malolactic fermentation. Lactic acid bacteria Oenococcus oeni metabolize with the release of CO2 and other by-products that significantly sour -tasting malic acid into the less sour -tasting lactic acid.
Biological Function
Malic acid is responsible for the sour taste of apple, and many other plants also contain malic acid. When the fruit ripens, decreases their content decreases while the sugar content. This effect is responsible for the propagation of the apple tree essential because the high content of malic acid in the fruit prevents animals eat it, and thus distribute the immature seeds.
In plants which have a Crassulacean acid metabolism ( CAM), is absorbed by breathing pores of the leaf carbon dioxide at night and fixed by the enzyme PEP carboxylase. By further reaction chain occurs while malate. Malate is the salt of malic acid and at night is stored in the vacuoles of CAM plants in the form of the acid. On the day of CO2 is again released from malic acid and fed directly to the Calvin cycle. CAM plants have called by the temporal separation of the reaction, also diurnal acid rhythm, the advantage of stomata to close during the day. Evaporation losses can be counteracted.