Malic acid

Short description: Dicarboxylic acid responsible for apple acidity

Not to be confused with maleic acid or malonic acid.

"Malate" redirects here. For the district in Manila, see Malate, Manila.

Malic acid

DL-Malic acid

Names
Preferred IUPAC name

2-Hydroxybutanedioic acid

Other names

* Hydroxybutanedioic acid
* 2-Hydroxysuccinic acid
* (L/D)-Malic acid
* (±)-Malic acid
* (S/R)-Hydroxybutanedioic acid

Identifiers

CAS Number

* 6915-15-7 Y

3D model (JSmol)

* Interactive image

ChEBI |

* CHEBI:6650 Y
* CHEBI:30796 D-(+)
* CHEBI:30797 L-(–)

ChEMBL |

* ChEMBL1455497 N

ChemSpider |

* 510 Y
* 83793 D-(+)-malic acid Y
* 193317 L-(–)-malic acid Y

EC Number |

* 230-022-8

IUPHAR/BPS

* 2480

KEGG |

* C00711 N
* C00497 D-(+)
* C00149 L-(–)

PubChem CID

* 525
* 92824 D-(+)
* 222656 L-(–)

UNII |

* 817L1N4CKP Y

InChI

* InChI=1S/C4H6O5/c5-2(4(8)9)1-3(6)7/h2,5H,1H2,(H,6,7)(H,8,9) Y

Key: BJEPYKJPYRNKOW-UHFFFAOYSA-N Y

* 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 | 134.09 g/mol
Appearance  | Colorless
Density | 1.609 g⋅cm−3
Melting point |  130 °C (266 °F; 403 K)

Solubility in water

| 558 g/L (at 20 °C)[1]
Acidity (pKa)  | pKa1 = 3.40
pKa2 = 5.20[2]
pKa3 = 14.5[3]
Hazards
GHS pictograms |
Flash point | 203 °C[4]
Related compounds

Other anions

| Malate

Related carboxylic acids

| Succinic acid
Tartaric acid
Fumaric acid

Related compounds

| Butanol
Butyraldehyde
Crotonaldehyde
Sodium malate

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

N verify (what is YN ?)
Infobox references

Tracking categories (test):

* SizeSet

Malic acid is an organic compound with the molecular formula HO
2CCH(OH)CH
2CO
2H. It is a dicarboxylic acid that is made by all living organisms, contributes to the 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 a metabolic intermediate in the citric acid cycle.

## Contents

* 1 Etymology
* 2 Biochemistry
* 3 In food
* 4 Production and main reactions
* 5 Plant defense
* 6 Interactive pathway map
* 7 See also
* 8 References
* 9 External links

## Etymology

The word 'malic' is derived from Latin mālum, meaning 'apple'. The related Latin word mālus, meaning 'apple tree',[citation needed] is used as the name of the genus Malus, which includes all apples and crabapples;[5] and is the origin of other taxonomic classifications such as Maloideae, Malinae, and Maleae.

## Biochemistry

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

* L-Malic acid (S)

* D-Malic acid (R)

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.

## In food

Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785.[6] Antoine Lavoisier in 1787 proposed the name acide malique, which is derived from the Latin word for apple, mālum--as is its genus name Malus.[7][8] In German it is named Äpfelsäure (or Apfelsäure) after plural or singular of a sour thing from the apple fruit, but the salt(s) are called Malat(e). Malic acid is the main acid in many fruits, including apricots, blackberries, blueberries, cherries, grapes, mirabelles, peaches, pears, plums, and quince,[9] and is present in lower concentrations in other fruits, such as citrus. It contributes to the sourness of unripe apples. Sour apples contain high proportions of the acid. It is present in grapes and in most wines with concentrations sometimes as high as 5 g/L.[10] It confers a tart taste to wine; the amount decreases with increasing fruit ripeness. The taste of malic acid is very clear and pure in rhubarb, a plant for which it is the primary flavor. It is also the compound responsible for the tart flavor of sumac spice. It is also a component of some artificial vinegar flavors, such as "salt and vinegar" flavored potato chips.[11]

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.[12]

Malic acid, when added to food products, is denoted by E number E296. It is sometimes 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,[13] US[14] and Australia and New Zealand[15] (where it is listed by its INS number 296).

Malic acid contains 10 kJ (2.39 kilocalories) of energy per gram.[16]

## Production and main reactions

Racemic malic acid is produced industrially by the double hydration of maleic anhydride. In 2000, American production capacity was 5,000 tons per year. The enantiomers may be separated by chiral resolution of the racemic mixture. S-Malic acid is obtained by fermentation of fumaric acid.[17]

Self-condensation of malic acid in the presence of fuming sulfuric acid gives the pyrone coumalic acid:[18]

2 HO
2CCH(OH)CH
2CO
2H → HO
2CC

2 \+ 2 CO + 4 H

Carbon monoxide and water are liberated during this reaction.

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.

L-malic acid is used to resolve α-phenylethylamine, a versatile resolving agent in its own right.[19]

## Plant defense

Soil supplementation with molasses increases microbial synthesis of malic acid. This is thought to occur naturally as part of soil microbe suppression of disease, so soil amendment with molasses can be used as a crop treatment in horticulture.[20]

## Interactive pathway map

Click on genes, proteins and metabolites below to link to respective articles. [§ 1]

[[File:

|{{{bSize}}}px|alt=Glycolysis and Gluconeogenesis edit]]

Glycolysis and Gluconeogenesis edit

1. ↑ The interactive pathway map can be edited at WikiPathways: "GlycolysisGluconeogenesis_WP534". http://www.wikipathways.org/index.php/Pathway:WP534.

## See also

* Acids in wine
* Citrate–malate shuttle
* Crassulacean acid metabolism
* Malate–aspartate shuttle
* Maleic acid, resulting from malic acid dehydration

## References

1. ↑ "chemBlink Database of Chemicals from Around the World". chemblink.com. http://chemblink.com/products/6915-15-7.htm.
2. ↑ Data for biochemical research (3rd ed.). Oxford: Clarendon Press. 1986. ISBN 0-19-855358-7. OCLC 11865673.
3. ↑ 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. ISSN 0966-0844. PMID 19288211.
4. ↑ "DL-Malic acid - (DL-Malic acid) SDS". https://www.merckmillipore.com/en/product/msds/MDA_CHEM-100383.
5. ↑ Peffley, Ellen. "Peffley: Crabapples steal the show in autumn" (in en-US). https://www.lubbockonline.com/story/lifestyle/home-garden/2021/11/23/peffley-crabapples-steal-show-autumn/8716819002/.
6. ↑ 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 den Åple-syran." ( ... I will henceforth call it apple acid.)
7. ↑ de Morveau, Lavoisier, Bertholet, and de Fourcroy, Méthode de Nomenclature Chimique (Paris, France: Cuchet, 1787), p. 108.
8. ↑ Jensen, William B. (June 2007). "The Origin of the Names Malic, Maleic, and Malonic Acid" (in en). Journal of Chemical Education 84 (6): 924. doi:10.1021/ed084p924. ISSN 0021-9584. Bibcode: 2007JChEd..84..924J. https://pubs.acs.org/doi/abs/10.1021/ed084p924.
9. ↑ Tabelle I of "Fruchtsäuren". http://www.spektrum.de/lexikon/biologie/fruchtsaeuren/25817.
10. ↑ Ough, C. S. (1988). Methods for analysis of musts and wines (2nd ed.). New York: J. Wiley. pp. 67. ISBN 0-471-62757-7. OCLC 16866762.
11. ↑ "The Science Behind Salt and Vinegar Chips". seriouseats.com. http://www.seriouseats.com/2012/09/the-best-salt-and-vinegar-chips-tasting-brands-most-acidic.html.
12. ↑ Malic Acid , Bartek Ingredients (retrieved 2 February 2012)
13. ↑ UK Food Standards Agency: "Current EU approved additives and their E Numbers". http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist.
14. ↑ "Food Additive Status List". FDA. 26 August 2021. https://www.hfpappexternal.fda.gov/scripts/fdcc/index.cfm?set=FoodSubstances. Retrieved 5 May 2022.
15. ↑ Australia New Zealand Food Standards Code"Standard 1.2.4 - Labelling of ingredients". 8 September 2011. http://www.comlaw.gov.au/Details/F2011C00827.
16. ↑ Greenfield, Heather; Southgate, D.A.T. (2003). Food composition data: production, management and use (2 ed.). Rome: Food and Agriculture Organization of the United Nations. p. 146. ISBN 978-92-5-104949-5. https://books.google.com/books?id=KQRzKDr9bgcC&pg=PA146. Retrieved 10 February 2014.
17. ↑ Karlheinz Miltenberge. "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_507.
18. ↑ Richard H. Wiley, Newton R. Smith (1951). "Coumalic acid". Organic Syntheses 31: 23. doi:10.15227/orgsyn.031.0023.
19. ↑ A. W. Ingersoll (1937). "D- and l-α-Phenylethylamine". Organic Syntheses 17: 80. doi:10.15227/orgsyn.017.0080.
20. ↑ Rosskopf, Erin; Di Gioia, Francesco; Hong, Jason C.; Pisani, Cristina; Kokalis-Burelle, Nancy (2020-08-25). "Organic Amendments for Pathogen and Nematode Control". Annual Review of Phytopathology (Annual Reviews) 58 (1): 277–311. doi:10.1146/annurev-phyto-080516-035608. ISSN 0066-4286. PMID 32853099. Bibcode: 2020AnRvP..58..277R.

## External links

* Calculator: Water and solute activities in aqueous malic acid

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Citric acid cycle metabolic pathway

Acetyl-CoA

\+ H
2O |

Oxaloacetate

NADH +H+

NAD+

Malate

H2O

Fumarate

FADH2

FAD

Succinate

CoA + ATP (GTP)

Pi \+ ADP (GDP)

Succinyl-CoA

|  | NADH + H+ \+ CO

CoA | NAD+

Citrate

cis-Aconitate

Isocitrate

NAD(P)+

NAD(P)H +  H+

Oxalosuccinate

2-oxoglutarate

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