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]]