Lactic acid 172474 225670616 2008-07-14T20:46:45Z MattieTK 434929 Reverted edits by [[Special:Contributions/92.9.61.122|92.9.61.122]] to last version by 68.35.111.91 (using [[WP:HG|Huggle]]) {{Refimprove|date=July 2008}} {{Chembox new | Name = Lactic acid | ImageFileL1 = Lactic-acid-skeletal.svg | ImageSizeL1 = 120px | ImageNameL1 = Skeletal formula of lactic acid | ImageFileR1 = Lactic-acid-3D-balls.png | ImageSizeR1 = 120px | ImageNameR1 = Ball-and-stick model of lactic acid | IUPACName = 2-hydroxypropanoic acid | Section1 = {{Chembox Identifiers | CASOther = 50-21-5<br /><small>L</small>: 79-33-4<br /><small>D</small>: 10326-41-7<br /><small>D</small>/<small>L</small>: 598-82-3 | SMILES = CC(O)C(=O)O }} | Section2 = {{Chembox Properties | Formula = C<sub>3</sub>H<sub>6</sub>O<sub>3</sub> | MolarMass = 90.08 g/mol | MeltingPt =<small>L</small>: 53 °C<br /><small>D</small>: 53 °C<br /><small>D</small>/<small>L</small>: 16.8 °C | BoilingPt = 122 °C @ 12 mmHg | pKa = 3.85 }} }} '''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]], and is a [[carboxylic acid]] with a [[chemical formula]] of C<sub>3</sub>H<sub>6</sub>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]]. 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. 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. Industrially, [[lactic acid fermentation]] is performed by ''[[Lactobacillus]]'' [[bacteria]], among others. These bacteria can operate in the [[mouth]]; the [[acid]] they produce is responsible for the [[tooth]] decay known as [[caries]]. In [[medicine]], lactate is one of the main components of Ringer's lactate or [[lactated Ringer's solution]] ([[Hartmann's Solution|Compound Sodium Lactate]] or [[Hartmann's Solution]] in the UK). This [[intravenous]] fluid consists of [[sodium]] and [[potassium]] [[cations]], with lactate and [[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)|burn injury]]. ==Exercise and lactate== During power exercises such as sprinting, 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]] * conversion to [[glucose]] via the [[Cori cycle]] in the liver through the process of [[gluconeogenesis]]. Contrary to popular belief, this increased concentration of lactate does not directly cause [[acidosis]], nor is it responsible for [[delayed onset muscle soreness]].<ref name=robergs>{{cite journal | author = R. Robergs, F. Ghiasvand, D. Parker | title = Biochemistry of exercise-induced metabolic acidosis | journal = Am J Physiol Regul Integr Comp Physiol | volume = 287 | issue = 3 | pages = R502–16 | year = 2004 | doi = 10.1152/ajpregu.00114.2004 | 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. 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, [[lactic acid fermentation|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, a natural process which facilitates the easier dissociation of [[Oxyhaemoglobin]] and allows easier transfer of oxygen from the blood<ref>Siggaard-Andersen, O & OH Gøthgen (1995) Oxygen and acid-base parameters of arterial and mixed venous blood. Relevant versus redundant. Acta Anaesthesiol Scand 39. Suppl 107, 21-27</ref>. This may be one factor, among many, that contributes to the acute muscular discomfort experienced shortly after intense exercise.{{Facts|date=February 2007}} 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.{{Fact|date=June 2007}} has been written to rebut the stoichiometric approach used by Robergs et al (2004).<ref name=robergs/> In using this stoichiometric process, Robergs et al. have ignored the causative factors (independent variables) of the concentration of hydrogen ions (denoted [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 an increase in [H<sup>+</sup>] to maintain electroneutrality. PCO<sub>2</sub> also causes an increase in [H<sup>+</sup>]. During exercise, the intramuscular lactate concentration and PCO<sub>2</sub> increase, causing an increase in [H<sup>+</sup>], and thus a decrease in pH. (See [[Le Chatelier's Principle|Le Chatelier's principle]]) ==Lactic acid as a polymer precursor== {{main|polylactic acid}} 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. Nowadays, lactic acid is used as a monomer for producing [[polylactic acid]] (PLA) which later has application as biodegradable plastic. This kind of plastic is a good option for substituting conventional plastic produced from petroleum oil because of low emission of carbon dioxide that can contribute to global warming. The commonly used process in producing lactic acid is via fermentation, and later to obtain the polylactic acid, the polymerization process follows. ==Lactic acid in foods== 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. 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", [[vegan]] products can contain lactic acid as an ingredient. 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> Lactic acid is also present in [[wheat beer]]s, especially [[lambic]], due to the activity of ''Pediococcus damnosus''.<ref>[http://ourworld.compuserve.com/homepages/pvosta/pcrbier1.htm The Lambic Beers<!-- Bot generated title -->]</ref> Lactic acid is widely used for inhibiting pathogenic bacteria like E.coli, Salmonella, Campylobacter and Listeria on animal carcasses like beef, pork and poultry during the slaughtering process. Potassium lactate, sodium lactate and calcium lactate are the neutralized salts of lactic acid. Potassium lactate is used in many fresh and cooked meat products for shelf life control, color preservation and reduction of sodium content. Sodium lactate has a mild saline taste and is therefore suitable for flavour enhancement in meat products as well. Sodium lactate is being produced as liquids as well as powders. Calcium lactate is popular for fortification and improved texture in emulsified meat products like frankfurters.<ref>Applications of lactates in meat and meat products, PURAC, a CSM company http://www.purac.com</ref> ==See also== *[[Cori cycle]] *[[Alanine cycle]] *[[Biodegradable Plastic]] *[[2-Hydroxybutyric acid]] ==References== {{reflist}} ==External links== *[http://www.time-to-run.com/theabc/lactic.htm Lactic acid and running: myths, legends and reality] *[http://www.smithsonianmag.com/science-nature/10022381.html Corn Plastic to the Rescue] [[Category:Food acidity regulators]] [[Category:Hydroxy acids]] [[Category:Exercise physiology]] [[Category:Food additives]] [[ar:حمض لاكتيك]] [[bg:Млечна киселина]] [[cs:Kyselina mléčná]] [[da:Mælkesyre]] [[de:Milchsäure]] [[et:Piimhape]] [[el:Γαλακτικό οξύ]] [[es:Ácido láctico]] [[eo:Lakta acido]] [[fr:Acide lactique]] [[is:Mjólkursýra]] [[it:Acido lattico]] [[he:חומצה לקטית]] [[lv:Pienskābe]] [[lb:Mëllechsaier]] [[lt:Pieno rūgštis]] [[hu:Tejsav]] [[nl:Melkzuur]] [[ja:乳酸]] [[no:Melkesyre]] [[nn:Mjølkesyre]] [[pl:Kwas mlekowy]] [[pt:Ácido láctico]] [[ro:Acid lactic]] [[ru:Молочная кислота]] [[sk:Kyselina mliečna]] [[su:Asam laktat]] [[fi:Maitohappo]] [[sv:Mjölksyra]] [[tr:Laktik asit]] [[zh:乳酸]]