Lactic acid: Difference between revisions
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! {{chembox header}}| '''{{{name|Lactic acid}}}''' |
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| align="center" colspan="2" bgcolor="#ffffff" | [[Image:Lactic-acid-skeletal.png|150px|Skeletal formula of lactic acid]] [[Image:Lactic-acid-3D-balls.png|150px|Ball-and-stick model of lactic acid]] |
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| [[IUPAC nomenclature|Chemical name]] |
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| {{{IUPAC|2-hydroxypropanoic acid}}} |
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| [[Chemical formula]] |
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| {{{formula|[[Carbon|C]]<sub>3</sub>[[Hydrogen|H]]<sub>6</sub>[[Oxygen|O]]<sub>3</sub>}}} |
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| [[Molecular mass]] |
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| {{{mol_mass|90.08}}} g/mol |
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|- |
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| [[CAS registry number|CAS number]] |
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| [{{{CAS|50-21-5}}}]<br><small>L</small>: [{{{CAS|79-33-4}}}]<br><small>D</small>: [{{{CAS|10326-41-7}}}]<br><small>D</small>/<small>L</small>: [{{{CAS|598-82-3}}}] |
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| [[Melting point]] |
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| <small>L</small>: 53 °C<br><small>D</small>: 53 °C<br><small>D</small>/<small>L</small>: 16.8 °C |
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| [[Boiling point]] |
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| {{{boiling_point|122}}} °C @ 12 mmHg |
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| [[Simplified molecular input line entry specification|SMILES]] |
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| {{{SMILES|CC(O)C(=O)O}}} |
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| {{chembox header}} | <small>[[wikipedia:Chemical infobox|Disclaimer and references]]</small> |
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<!-- Image with unknown copyright status removed: [[Image:Lacticacid.JPG|128px|right|thumb|[[Space-filling model]] of lactic acid]] --> |
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''For the production of milk by mammals, see [[Lactation]].'' |
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'''Lactic acid''' ([[IUPAC]] [[systematic name]]: '''2-hydroxypropanoic acid'''), also known as '''milk acid''', is a [[chemical compound]] that plays a role in several [[biochemistry|biochemical]] processes. It was first isolated in 1780 by a Swedish chemist, [[Carl Wilhelm Scheele|Carl Wilhelm Scheele]], and is a [[carboxylic acid]] with a [[chemical formula]] of [[Carbon|C]]<sub>3</sub>[[Hydrogen|H]]<sub>6</sub>[[Oxygen|O]]<sub>3</sub>. It has a [[hydroxyl]] group adjacent to the [[carboxyl]] group, making it an [[alpha hydroxy acid]] (AHA). In solution, it can lose a [[proton]] from the acidic group, producing the '''lactate''' [[ion]] CH<sub>3</sub>CH(OH)COO<sup>−</sup>. It is miscible with water or ethanol, and is [[hygroscopy|hygroscopic]]. |
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Lactic acid is [[Chirality (chemistry)|chiral]] and has two [[optical isomer]]s. One is known as <small>L</small>-(+)-lactic acid or (''S'')-lactic acid and the other, its mirror image, is <small>D</small>-(-)-lactic acid or (''R'')-lactic acid. <small>L</small>-(+)-Lactic acid is the biologically important isomer. |
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In animals, <small>L</small>-lactate is constantly produced from [[pyruvate]] via the [[enzyme]] [[lactate dehydrogenase]] (LDH) in a process of [[fermentation (biochemistry)|fermentation]] during normal [[metabolism]] and [[exercise]]. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal which is governed by a number of factors including: monocarboxylate transporters, concentration and isoform of LDH and oxidative capacity of tissues. The concentration of [[blood]] lactate is usually 1-2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion. |
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Lactic acid fermentation is also performed by ''[[Lactobacillus]]'' [[bacteria]]. These bacteria can operate in the [[mouth]]; the [[acid]] they produce is responsible for the [[tooth]] decay known as [[caries]]. |
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In [[medicine]], lactate is one of the main components of [[Ringer's lactate]] or lactated Ringer's solution. This [[intravenous]] fluid consists of [[sodium]] and [[potassium]] [[cations]], with lactate[[chloride]] [[anions]], in solution with distilled [[water]] in concentration so as to be [[isotonic]] compared to [[human]] [[blood]]. It is most commonly used for fluid [[resuscitation]] after blood loss due to [[Physical trauma|trauma]], [[surgery]] or a [[burn]] injury. |
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== Exercise and lactate == |
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During intense exercise, such as sprinting type activities, when the rate of demand for energy is high, lactate is produced faster than the ability of the tissues to remove it and lactate concentration begins to rise. This is a beneficial process since the regeneration of [[Nicotinamide adenine dinucleotide|NAD<sup>+</sup>]] ensures that energy production is maintained and exercise can continue. The increased lactate produced can be removed in a number of ways including: [[oxidation]] to pyruvate by well-oxygenated [[muscle]] [[cell (biology)|cells]] which is then directly used to fuel the [[citric acid cycle]] and conversion to [[glucose]] via the [[Cori cycle]] in the liver through the process of [[gluconeogenesis]]. |
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Contrary to popular belief, this increased concentration of lactate does not directly cause [[acidosis]], nor is it responsible for [[delayed onset muscle soreness]].<ref>{{cite journal | author = Robergs R, Ghiasvand F, Parker D | title = Biochemistry of exercise-induced metabolic acidosis. | journal = Am J Physiol Regul Integr Comp Physiol | volume = 287 | issue = 3 | pages = R502-16 | year = 2004 | id = PMID 15308499}}</ref> This is because lactate itself is not capable of releasing a [[proton]], and secondly, the acidic form of lactate, lactic acid, cannot be formed under normal circumstances in human tissues. Analysis of the glycolytic pathway in humans indicates that there are not enough hydrogen ions present in the glycolytic intermediates to produce lactic or any other acid. |
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The [[acidosis]] that is associated with increases in lactate concentration during heavy exercise arises from a separate reaction. When [[Adenosine triphosphate|ATP]] is [[Hydrolysis|hydrolysed]], a hydrogen ion is released. ATP-derived hydrogen ions are primarily responsible for the decrease in pH. During intense exercise, [[aerobic metabolism]] cannot produce ATP quickly enough to supply the demands of the muscle. As a result, [[anaerobic metabolism]] becomes the dominant energy producing pathway as it can form ATP at high rates. Due to the large amounts of ATP being produced and hydrolysed in a short period of time, the [[buffer solution|buffering]] systems of the tissues are overcome, causing pH to fall and creating a state of acidosis. This may be one factor, among many, that contributes to the acute muscular discomfort experienced shortly after intense exercise.{{Facts|date=February 2007}} |
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The effect of lactate on acidosis has been the topic of many recent conferences in the field of exercise physiology. Robergs et al. have accurately chased the proton movement that occurs during glycolysis. However, in doing so, they have suggested that [H<sup>+</sup>] is an independent variable that determines its own concentration. A recent review by Lindinger et al. has been written to rebut the stoichiometric approach used by Robergs et al. In using this stoichiometric process, Robergs et al. have ignored the causitive factors (independent variables) of [H<sup>+</sup>]. These factors are strong ion difference [SID], PCO<sub>2</sub>, and weak acid buffers. Lactate is a strong anion, and causes a reduction in [SID] which causes and increase in [H<sup>+</sup>] to maintain electroneutrality. PCO<sub>2</sub> also causes an increase in [H<sup>+</sup>]. During exercise, intramuscular [lactate] and PCO<sub>2</sub> increase, causing an increase in [H<sup>+</sup>], and thus a decrease in pH. It is unclear as to why Robergs et al. have ignored these independent variables in their review. [SID], PCO<sub>2</sub>, and [weak acid buffer] have been measured during exercise by Jones et al. The reader interested in acid-base balance during exercise is recommended to consult work by Peter Stewart. |
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== Lactic acid in food == |
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Lactic acid is primarily found in sour [[milk]] products, such as: [[koumiss]], leban, [[yogurt]], [[kefir]] and some [[cottage cheese]]s. The [[casein]] in fermented milk is coagulated (curdled) by lactic acid. |
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Although it can be [[fermentation (food)|fermented]] from [[lactose]] (milk sugar), most commercially used lactic acid is derived by using bacteria such as ''[[Bacillus acidilacti]]'', ''[[Lactobacillus delbueckii]]'' or ''[[Lactobacillus bulgaricus]]'' to ferment carbohydrates from nondairy sources such as [[cornstarch]], [[potato]]es and [[molasses]]. Thus, although it is commonly known as "milk acid", products claiming to be [[vegan]] do sometimes feature lactic acid as an ingredient. |
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Lactic acid may also be found in various processed foods, usually either as a pH adjusting ingredient, or as a [[preservative]] (either as [[antioxidant]] or for control of pathogenic micro-organisms). It may also be used as a fermentation booster in rye and sourdough [[bread]]s.<ref>"Food Applications". Galactic Div. of Finasucre. 2006. http://www.lactic.com/</ref> |
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== Lactic acid as a polymer precursor == |
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Two molecules of lactic acid can be dehydrated to [[lactide]], a cyclic lactone. A variety of [[catalysts]] can polymerise lactide to either [[heterotactic]] or [[syndiotactic]] [[Polylactic acid|polylactide]], which as [[biodegradable]] [[polyester]]s with valuable (''inter alia'') medical properties are currently attracting much attention. |
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==References== |
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<references /> |
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==See also== |
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*[[Cori cycle]] |
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*[[Alanine cycle]] |
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==External links== |
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*[http://www.time-to-run.com/theabc/lactic.htm Lactic acid and running: myths, legends and reality] |
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* [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15308499&query_hl=3&itool=pubmed_docsum Biochemistry of exercise-induced metabolic acidosis.] |
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{{ChemicalSources}} |
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[[Category:Hydroxy acids]] |
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[[Category:Exercise physiology]] |
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[[Category:Food additives]] |
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[[ar:حمض لاكتيك]] |
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[[bg:Млечна киселина]] |
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[[cs:Kyselina mléčná]] |
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[[da:Mælkesyre]] |
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[[de:Milchsäure]] |
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[[el:Γαλακτικό οξύ]] |
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[[es:Ácido láctico]] |
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[[eo:Lakta acido]] |
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[[fr:Acide lactique]] |
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[[is:Mjólkursýra]] |
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[[it:Acido lattico]] |
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[[he:חומצה לקטית]] |
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[[lb:Mëllechsaier]] |
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[[nl:Melkzuur]] |
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[[ja:乳酸]] |
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[[no:Melkesyre]] |
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[[nn:Mjølkesyre]] |
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[[pl:Kwas mlekowy]] |
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[[pt:Ácido láctico]] |
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[[ro:Acid lactic]] |
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[[ru:Молочная кислота]] |
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[[sk:Kyselina mliečna]] |
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[[su:Asam laktat]] |
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[[fi:Maitohappo]] |
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[[sv:Mjölksyra]] |
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[[tr:Laktik asit]] |
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[[zh:乳酸]] |
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