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Malic acid

Names
IUPAC name hydroxybutanedioic acid
Other names L-Malic acid D-Malic acid (-)-Malic acid (+)-Malic acid (S)-Hydroxybutanedioic acid (R)-Hydroxybutanedioic acid
Identifiers
CAS Number	6915-15-7
3D model (JSmol)	Interactive image
ChEBI	CHEBI:6650
ChemSpider	510 83793 D-(+)-malic acid 193317 L-(-)-malic acid
ECHA InfoCard	100.027.293
EC Number	230-022-8
E number	E296 (preservatives)
KEGG	D04843
PubChem CID	525
UNII	817L1N4CKP
CompTox Dashboard (EPA)	DTXSID0027640
InChI InChI=1S/C4H6O5/c5-2(4(8)9)1-3(6)7/h2,5H,1H2,(H,6,7)(H,8,9)Key: BJEPYKJPYRNKOW-UHFFFAOYSA-N InChI=1/C4H6O5/c5-2(4(8)9)1-3(6)7/h2,5H,1H2,(H,6,7)(H,8,9)Key: BJEPYKJPYRNKOW-UHFFFAOYAM
SMILES O=C(O)CC(O)C(=O)O
Properties
Chemical formula	C4H6O5
Molar mass	134.087 g·mol
Density	1.609 g cm
Melting point	130 °C (266 °F; 403 K)
Solubility in water	558 g/L (at 20 °C)
Acidity (pKa)	pKa1 = 3.40, pKa2 = 5.20
Related compounds
Other anions	malate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Y verify (what is  ?) Infobox references

Malic acid is an organic compound with the formula HO₂CCH₂CHOHCO₂H. It is a dicarboxylic acid which is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used as a food additive. 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.

Biochemistry

L-Malic acid is the naturally occurring form, whereas a mixture of L- and D-malic acid is produced synthetically.

• L-Malic acid
• D-Malic acid

Malate plays an important role in biochemistry. In the C4 carbon fixation process, malate is a source of CO₂ in the Calvin cycle. In the citric acid cycle, (S)-malate is an intermediate, formed by the addition of an -OH group on the si face of fumarate. It can also be formed from pyruvate via anaplerotic reactions.

Malate is also synthesized by the carboxylation of phosphoenolpyruvate 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 the solute potential, allowing water to enter the cell and promote aperture of the stomata.

Malic acid in food

Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785. Antoine Lavoisier in 1787 proposed the name acide malique which is derived from the Latin word for apple, mālum. 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. Malic acid occurs naturally in all fruits and many vegetables, and is generated in fruit metabolism.

Malic acid, when added to food products, is denoted by E number E296. Malic acid is the source of extreme tartness in USA-produced 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 stating that excessive consumption can cause irritation of the mouth. It is approved for use as a food additive in the EU, USA and Australia and New Zealand (where it is listed by its INS number 296).

Production and main reactions

Malic acid is produced industrially by the double hydration of maleic anhydride.

Self-condensation of malic acid with fuming sulfuric acid gives the pyrone coumalic acid:

Malic acid was important in the discovery of the Walden inversion and the Walden cycle, in which (-)-malic acid first is converted into (+)-chlorosuccinic acid by action of phosphorus pentachloride. Wet silver 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.

Interactive pathway map

Click on genes, proteins and metabolites below to link to respective articles.

1. The interactive pathway map can be edited at WikiPathways: "TCACycle_WP78".

See also

• Acids in wine
• Crassulacean acid metabolism
• Malate-aspartate shuttle

References

1. chemBlink Online Database of Chemicals from Around the World
2. Dawson, R. M. C. et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
3. The Origin of the Names Malic, Maleic, and Malonic Acid Jensen, William B. J. Chem. Educ. 2007, 84, 924. Abstract
4. "Methods For Analysis of Musts and Wines", Ough and Amerine, John Wiley and Sons, 2nd Edition, 1988, page 67
5. Malic Acid, Bartek Ingredients (retrieved 2 February 2012)
6. UK Food Standards Agency: "Current EU approved additives and their E Numbers". Retrieved 2011-10-27.
7. US Food and Drug Administration: "Listing of Food Additives Status Part II". Retrieved 2011-10-27.
8. Australia New Zealand Food Standards Code"Standard 1.2.4 - Labelling of ingredients". Retrieved 2011-10-27.
9. Karlheinz Miltenberger "Hydroxycarboxylic Acids, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry,2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13 507
10. Richard H. Wiley and Newton R. Smith (1963). "Coumalic acid". Organic Syntheses; Collected Volumes, vol. 4, p. 201.

External links

• Calculator: Water and solute activities in aqueous malic acid

v t e Citric acid cycle metabolic pathway
Acetyl-CoA + H2O Oxaloacetate NADH +H NAD Malate   H2O Fumarate FADH2 FAD Succinate CoA + ATP (GTP) Pi + ADP (GDP) Succinyl-CoA NADH + H + CO2 CoA NAD Citrate   H2O cis-Aconitate H2O   Isocitrate NAD(P) NAD(P)H +  H Oxalosuccinate   CO2 2-oxoglutarate

• Cellular respiration
• Citric acid cycle compounds
• Cosmetics chemicals
• Dicarboxylic acids
• Food acidity regulators
• Hydroxy acids
• Acids in wine