Malic acid
243074
225229445
2008-07-12T16:08:36Z
Groyolo
416036
Hyphenated modifier.
{{Distinguish|Maleic acid}}
{{redirect|Malate|the district in Manila|Malate, Manila}}
{{Chembox new
| Name = Malic acid
| ImageFile = Malic acid2.png
| ImageSize = 180px
| ImageName = Malic acid
| IUPACName = hydroxybutanedioic acid
| Section1 = {{Chembox Identifiers
| CASNo = 617-48-1
| CASNo = 6915-15-7
| EINECS = 230-022-8
| CoE = 17
| FEMA = 2655
| JECFA = 619
}}
| Section2 = {{Chembox Properties
| Formula = C<sub>4</sub>H<sub>6</sub>O<sub>5</sub>
| MolarMass = 134.09 g/mol
| MeltingPt = 130 °C
| Density = 1.609 g/cm³
| pKa = p''K''a<sub>1</sub> = 3.4, p''K''a<sub>2</sub> = 5.13
| Solubility = 558 g/l (at 20 °C)<ref>[http://www.chemblink.com/products/6915-15-7.htm chemBlink Online Database of Chemicals from Around the World]</ref>
}}
}}
'''Malic acid''' is an [[organic compound]] with the formula HO<sub>2</sub>CCH<sub>2</sub>CHOHCO<sub>2</sub>H. This di[[carboxylic acid]] is the active ingredient in many [[sour]] or tart foods. The [[salt (chemistry)|salts]] and [[ester]]s of malic acid are known as '''malates'''. Malate anion is an intermediate in the [[citric acid cycle]] along with [[fumaric acid|fumarate]]. Ca. 1M kg/y are produced by the hydration of [[maleic anhydride]].<ref>Karlheinz Miltenberger, "Hydroxycarboxylic Acids, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH: Weinheim, 2005.</ref>
==History==
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''.<ref>''The Origin of the Names Malic, Maleic, and Malonic Acid'' Jensen, William B. J. Chem. Educ. '''2007''', 84, 924. [http://jchemed.chem.wisc.edu/Journal/Issues/2007/Jun/abs924.html Abstract]</ref>
==Biology==
Malate plays an important role in [[biochemistry]]. In biological sources, malic acid is [[homochiral]] and only exists as the (-)-malic acid [[enantiomer]]. In the [[C4 carbon fixation]] process, malate is a source of [[carbon dioxide|CO<sub>2</sub>]] in the [[Calvin cycle]]. In the [[citric acid cycle]], (''S'')-malate is an intermediate formed by the addition of an [[alcohol|-OH]] group on the ''si'' face of fumarate; it can also be formed from pyruvate via [[anaplerotic reactions]]. [[Malate dehydrogenase]] catalyzes the reversible conversion of malate into [[oxaloacetate]] using [[Nicotinamide adenine dinucleotide|NAD<sup>+</sup>]] as a [[cofactor]]. Malate is also produced from starch in guard cells of plant leaves. A build up of malate leads to a low water potential. Water then flows into the guard cells causing the [[stoma]] to open. However, this process does not always induce the opening of stomata.
Malic acid contributes to the sourness of green [[apple]]s. Malic acid is present in [[grape]]s. 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]].
==As a food additive==
Malic acid, when added to food products, is denoted by [[E number]] E296. Malic acid is the source of extreme tartness in so-called "extreme candy", for example [[Warheads (confectionery)|Mega Warheads]] or [[Sour Punch]] candies. It is also used with or in place of the less sour [[citric acid]] in sour sweets such as [[Jolly Rancher]]s, [[SweeTarts]] and Salt & Vinegar flavor potato chips. These sweets are sometimes labeled with a warning that excessive consumption can cause irritation of the mouth.
==Chemistry==
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 PCl<sub>5</sub> to the (-)-chlorosuccinic acid. The cycle is completed when silver oxide takes this compound back to (-)-malic acid.
[[Self-condensation]] of malic acid with [[fuming sulfuric acid]] gives the [[pyrone]] '''coumalic acid''':<ref>{{OrgSynth | title = Coumaric acid | collvol = 4 | collvolpages = 201 | year = 1963 | prep = cv4p0201 | author = Richard H. Wiley and Newton R. Smith}}</ref>
:[[Image:CoumaricAcidSynthesis.png|400px|Coumalic Acid Synthesis]]
==See also==
*[[Malate-aspartate shuttle]]
*Two other dicarboxylic acids have similar names and should not be confused with malic acid:
**[[Maleic acid]]
**[[Malonic acid]]
==References==
{{Reflist}}
{{citric acid cycle}}
[[Category:Cellular respiration]]
[[Category:Citric acid cycle compounds]]
[[Category:Cosmetic chemicals]]
[[Category:Dicarboxylic acids]]
[[Category:Food acidity regulators]]
[[Category:Hydroxy acids]]
[[Category:Oenology]]
[[ca:Àcid màlic]]
[[cs:Kyselina jablečná]]
[[da:Æblesyre]]
[[de:Äpfelsäure]]
[[el:Μηλικό οξύ]]
[[es:Ácido málico]]
[[fr:Acide malique]]
[[hr:Jabučna kiselina]]
[[it:Acido malico]]
[[lv:Ābolskābe]]
[[hu:Almasav]]
[[nl:Appelzuur]]
[[ja:リンゴ酸]]
[[pl:Kwas jabłkowy]]
[[pt:Ácido málico]]
[[ru:Яблочная кислота]]
[[fi:Omenahappo]]
[[sv:Äppelsyra]]
[[zh:苹果酸]]