Lactic acid: Difference between revisions

Latest revision as of 23:26, 19 November 2025

Template:Short description Template:Use dmy dates Template:Chembox Lactic acid is an organic acid with the molecular formula C₃H₆O₃. In its solid state, it is white and miscible with water.^[1] When dissolved, it forms a colorless solution. Production includes both artificial synthesis and natural sources. Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of a hydroxyl group adjacent to the carboxyl group. It is a synthetic intermediate in many organic synthesis industries and in various biochemical industries. The conjugate base of lactic acid is called lactate (or the lactate anion). The name of the derived acyl group is lactoyl.

In solution, it can ionize by a loss of a proton to produce the lactate ion Template:Chem, also known as 2-hydroxypropanoate. Compared to acetic acid, its pK_a is 1 unit less, meaning that lactic acid is ten times more acidic than acetic acid. This higher acidity is the consequence of intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group.

Lactic acid is chiral, consisting of two enantiomers. One is known as Template:Sc-lactic acid, (S)-lactic acid, or (+)-lactic acid, and the other, its mirror image, is Template:Sc-lactic acid, (R)-lactic acid, or (−)-lactic acid. A mixture of the two in equal amounts is called Template:Sc-lactic acid, or racemic lactic acid. Lactic acid is hygroscopic. Template:Sc-Lactic acid is miscible with water and with ethanol above its melting point, which is Template:Cvt. Template:Sc-Lactic acid and Template:Sc-lactic acid have a higher melting point. Lactic acid produced by fermentation of milk is often racemic, although certain species of bacteria produce solely Template:Sc-lactic acid.^[2] On the other hand, lactic acid produced by fermentation in animal muscles has the (Template:Sc) enantiomer and is sometimes called "sarcolactic" acid, from the Greek Template:Transliteration, meaning "flesh".

In animals, Template:Sc-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise.^[3] 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.^[3] This reaction is reversible and redox-linked: LDH reduces pyruvate to lactate using NADH as an electron donor, simultaneously regenerating NAD⁺ required for glycolysis under anaerobic conditions.^[4] The concentration of blood lactate is usually 1–2Template:Nbsp Template:Abbrlink at rest, but can rise to over 20Template:NbspmM during intense exertion and as high as 25Template:NbspmM afterward.^[5]^[6] In addition to other biological roles, Template:Sc-lactic acid is the primary endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA₁), which is a G_i/o-coupled G protein-coupled receptor (GPCR).^[7]^[8]

In industry, lactic acid fermentation is performed by lactic acid bacteria, which convert simple carbohydrates such as glucose, sucrose, or galactose to lactic acid. These bacteria can also grow in the mouth; the acid they produce is responsible for the tooth decay known as cavities.^[9]^[10]^[11]^[12] In medicine, lactate is one of the main components of lactated Ringer's solution and Hartmann's solution. These intravenous fluids consist of sodium and potassium cations along with lactate and chloride anions in solution with distilled water, generally in concentrations isotonic with human blood. It is most commonly used for fluid resuscitation after blood loss due to trauma, surgery, or burns.

Lactic acid is produced in human tissues when the demand for oxygen is limited by the supply. This occurs during tissue ischemia when the flow of blood is limited as in sepsis or hemorrhagic shock. It may also occur when demand for oxygen is high, such as with intense exercise. The process of lactic acidosis produces lactic acid, which results in an oxygen debt, which can be resolved or repaid when tissue oxygenation improves.^[13]

History

Swedish chemist Carl Wilhelm Scheele was the first person to isolate lactic acid in 1780 from sour milk.^[14] The name reflects the lact- combining form derived from the Latin word Script error: No such module "Lang"., meaning "milk". In 1808, Jöns Jacob Berzelius discovered that lactic acid (actually Template:Sc-lactate) is also produced in muscles during exertion.^[15] Its structure was established by Johannes Wislicenus in 1873.

In 1856, the role of Lactobacillus in the synthesis of lactic acid was discovered by Louis Pasteur. This pathway was used commercially by the German pharmacy Boehringer Ingelheim in 1895.Script error: No such module "Unsubst".

Due to a combination of geographic and infrastructural factors, the Soviet Union, as well as several other members of the Warsaw Pact, experienced chronic shortages of citric and malic acid, among others.Script error: No such module "Unsubst". In order to combat this issue, the Narkomzem (Soviet Ministry of Agriculture) invested heavily in the development of suitable lactobacillus strains, which were able to produce lactic acid with relatively high efficiency from crude molasses feedstock.^[16] Despite synthetic citric acid being produced in some quantities across the Warsaw Pact, it proved far more difficult to purify, leading to lactic acid being, on average, a quarter of the cost of citric acid. The continued use of lactic acid in some Eastern European and Central Asian food production in the modern day, in favor of the more common citric or malic acids, lends it a distinctive flavor.Script error: No such module "Unsubst".

Global demand for lactic acid continues to expand, with an estimated annual growth rate of 5–8% driven by the increasing use of biodegradable plastics, green solvents, and pharmaceutical intermediates. Worldwide production exceeded 1.5 million tonnes by the early 2020s, up from roughly 275,000 tonnes in 2006, and is projected to keep rising as biobased materials replace petroleum-derived products.^[17] Major producers include NatureWorks LLC, Purac, Galactic, and several Chinese manufacturers. NatureWorks operates one of the world’s largest polylactic acid (PLA) facilities in Blair, Nebraska, with a production capacity of about 140,000 tonnes per year, supplying feedstock for a wide range of biodegradable packaging and fiber applications.^[18]

Production

Lactic acid is produced industrially by bacterial fermentation of carbohydrates, or by chemical synthesis from acetaldehyde.^[19] Template:As of, lactic acid was produced predominantly (70–90%)^[20] by fermentation. Production of racemic lactic acid consisting of a 1:1 mixture of Template:Sc and Template:Sc stereoisomers, or of mixtures with up to 99.9% Template:Sc-lactic acid, is possible by microbial fermentation. Industrial production of the D-lactic acid enantiomer is technically more challenging because most naturally occurring lactic acid bacteria preferentially produce the L-form; obtaining high optical purity of D-lactic acid therefore requires genetically engineered microorganisms or specific D-lactate dehydrogenases.^[18]

Fermentative production

Fermented milk products are obtained industrially by fermentation of milk or whey by Lactobacillus bacteria: Lactobacillus acidophilus, Lacticaseibacillus casei (Lactobacillus casei), Lactobacillus delbrueckii subsp. bulgaricus (Lactobacillus bulgaricus), Lactobacillus helveticus, Lactococcus lactis , Bacillus amyloliquefaciens, and Streptococcus salivarius subsp. thermophilus (Streptococcus thermophilus).Script error: No such module "Unsubst".

As a starting material for industrial production of lactic acid, almost any carbohydrate source containing Template:Chem (pentose sugar) and Template:Chem (hexose sugar) can be used. Pure sucrose, glucose from starch, raw sugar, and beet juice are frequently used.^[21] Lactic acid producing bacteria can be divided in two classes: homofermentative bacteria like Lactobacillus casei and Lactococcus lactis, producing two moles of lactate from one mole of glucose, and heterofermentative species, producing one mole of lactate from one mole of glucose, as well as carbon dioxide and acetic acid/ethanol.^[22]

Chemical production

Racemic lactic acid is synthesized industrially by reacting acetaldehyde with hydrogen cyanide and hydrolysing the resultant lactonitrile. When hydrolysis is performed by hydrochloric acid, ammonium chloride forms as a by-product; the Japanese company Musashino is one of the last big manufacturers of lactic acid by this route.^[23] Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials (vinyl acetate, glycerol, etc.) by application of catalytic procedures.^[24]

Biology

Molecular biology

Template:Sc-Lactic acid is the primary endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA₁), a G_i/o-coupled G protein-coupled receptor (GPCR).^[7]^[8]

Metabolism and exercise

Script error: No such module "Labelled list hatnote". During power exercises such as sprinting, when the rate of demand for energy is high, glucose is broken down and oxidized to pyruvate, and lactate is then produced from the pyruvate faster than the body can process it, causing lactate concentrations to rise. The production of lactate is beneficial for NAD⁺ regeneration (pyruvate is reduced to lactate while NADH is oxidized to NAD⁺), which is used up in oxidation of glyceraldehyde 3-phosphate during production of pyruvate from glucose, and this ensures that energy production is maintained and exercise can continue. During intense exercise, the respiratory chain cannot keep up with the amount of hydrogen ions that join to form NADH, and cannot regenerate NAD⁺ quickly enough, so pyruvate is converted to lactate to allow energy production by glycolysis to continue.^[25]

The resulting lactate can be used in two ways:

Oxidation back to pyruvate by well-oxygenated muscle cells, heart cells, and brain cells
- Pyruvate is then directly used to fuel the Krebs cycle
Conversion to glucose via gluconeogenesis in the liver and release back into circulation by means of the Cori cycle^[26]
- If blood glucose concentrations are high, the glucose can be used to build up the liver's glycogen stores.

Lactate is continually formed at rest and during all exercise intensities. Lactate serves as a metabolic fuel being produced and oxidatively disposed in resting and exercising muscle and other tissues.^[25] Some sources of excess lactate production are metabolism in red blood cells, which lack mitochondria that perform aerobic respiration, and limitations in the rates of enzyme activity in muscle fibers during intense exertion.^[26] Lactic acidosis is a physiological condition characterized by accumulation of lactate (especially Template:Sc-lactate), with formation of an excessively high proton concentration [H⁺] and correspondingly low pH in the tissues, a form of metabolic acidosis.^[25]

The first stage in metabolizing glucose is glycolysis, the conversion of glucose to pyruvate⁻ and H⁺:

Template:Chem2

When sufficient oxygen is present for aerobic respiration, the pyruvate is oxidized to Template:Chem2 and water by the Krebs cycle, in which oxidative phosphorylation generates ATP for use in powering the cell. When insufficient oxygen is present, or when there is insufficient capacity for pyruvate oxidation to keep up with rapid pyruvate production during intense exertion, the pyruvate is converted to lactate⁻ by lactate dehydrogenase), a process that absorbs these protons:^[27]

Template:Chem2

The combined effect is:

Template:Chem2

The production of lactate from glucose (Template:Chem2), when viewed in isolation, releases two H⁺. The H⁺ are absorbed in the production of ATP, but H⁺ is subsequently released during hydrolysis of ATP:

Template:Chem2

Once the production and use of ATP is included, the overall reaction is

Template:Chem2

The resulting increase in acidity persists until the excess lactate and protons are converted back to pyruvate, and then to glucose for later use, or to Template:Chem2 and water for the production of ATP.^[25]

pH Regulation

Lactate production and export contribute significantly to intracellular pH regulation in metabolically active tissues. In skeletal muscle, accumulation of lactic acid lowers intracellular pH, and monocarboxylate transporters facilitate the efflux of both lactate and H⁺, thereby helping maintain acid-base homeostasis and delaying fatigue.^[28]

Neural tissue energy source

Although glucose is usually assumed to be the main energy source for living tissues, there is evidence that lactate, in preference to glucose, is preferentially metabolized by neurons in the brains of several mammalian species that include mice, rats, and humans.^[29]^[30]^[25] According to the lactate-shuttle hypothesis, glial cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons.^[31]^[32] Because of this local metabolic activity of glial cells, the extracellular fluid immediately surrounding neurons strongly differs in composition from the blood or cerebrospinal fluid, being much richer with lactate, as was found in microdialysis studies.^[29]

Brain development metabolism

Some evidence suggests that lactate is important at early stages of development for brain metabolism in prenatal and early postnatal subjects, with lactate at these stages having higher concentrations in body liquids, and being utilized by the brain preferentially over glucose.^[29] It was also hypothesized that lactate may exert a strong action over GABAergic networks in the developing brain, making them more inhibitory than it was previously assumed,^[33] acting either through better support of metabolites,^[29] or alterations in base intracellular pH levels,^[34]^[35] or both.^[36]

Studies of brain slices of mice show that β-hydroxybutyrate, lactate, and pyruvate act as oxidative energy substrates, causing an increase in the NAD(P)H oxidation phase, that glucose was insufficient as an energy carrier during intense synaptic activity and, finally, that lactate can be an efficient energy substrate capable of sustaining and enhancing brain aerobic energy metabolism in vitro.^[37] The study "provides novel data on biphasic NAD(P)H fluorescence transients, an important physiological response to neural activation that has been reproduced in many studies and that is believed to originate predominantly from activity-induced concentration changes to the cellular NADH pools."^[38]

Lactate can also serve as an important source of energy for other organs, including the heart and liver. During physical activity, up to 60% of the heart muscle's energy turnover rate derives from lactate oxidation.^[14]

Blood testing

File:Blood values sorted by mass and molar concentration.png

Reference ranges for blood tests, comparing lactate content (shown in violet at center-right) to other constituents in human blood

Blood tests for lactate are performed to determine the status of the acid base homeostasis in the body. Blood sampling for this purpose is often arterial (even if it is more difficult than venipuncture), because lactate levels differ substantially between arterial and venous, and the arterial level is more representative for this purpose.

Reference ranges
	Lower limit	Upper limit	Unit
Venous	4.5^[39]	19.8^[39]	mg/dL
Venous	0.5^[40]	2.2^[40]	mmol/L
Arterial	4.5^[39]	14.4^[39]	mg/dL
Arterial	0.5^[40]	1.6^[40]	mmol/L

During childbirth, lactate levels in the fetus can be quantified by fetal scalp blood testing.

Uses

In 2023, lactate was the 289th most commonly prescribed medication in the United States, with more than 500,000 prescriptions.^[41]^[42]

Polymer precursor

Template:Main article

Two molecules of lactic acid can be dehydrated to the lactone lactide. In the presence of catalysts lactide polymerize to either atactic or syndiotactic polylactide (PLA), which are biodegradable polyesters. PLA is an example of a plastic that is not derived from petrochemicals.

Pharmaceutical and cosmetic applications

Lactic acid is also employed in pharmaceutical technology to produce water-soluble lactates from otherwise-insoluble active ingredients. It finds further use in topical preparations and cosmetics to adjust acidity and for its disinfectant and keratolytic properties.

Lactic acid containing bacteria have shown promise in reducing oxaluria with its descaling properties on calcium compounds.^[43]

Foods

Fermented food

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Lactic acid is found in many fermented foods.

Sour milk products, such as kumis, laban, yogurt, kefir, and some cottage cheeses, derive their flavor from lactic acid. The casein in fermented milk is coagulated (curdled) by lactic acid.
Lactic acid is also responsible for the sour flavor of sourdough bread.
Some beers (sour beer) purposely contain lactic acid, one such type being Belgian lambics. Most commonly, this is produced naturally by various strains of bacteria. These bacteria ferment sugars into acids, unlike the yeast that ferment sugar into ethanol. After cooling the wort, yeast and bacteria are allowed to "fall" into the open fermenters. Brewers of more common beer styles would ensure that no such bacteria are allowed to enter the fermenter. Other sour styles of beer include Berliner weisse, Flanders red and American wild ale.^[44]^[45]
In winemaking, a bacterial process, natural or controlled, is often used to convert the naturally present malic acid to lactic acid, to reduce the sharpness and for other flavor-related reasons. This malolactic fermentation is undertaken by lactic acid bacteria.
Pickling vegetables in brine creates a sour flavor as bacteria convert sugars into lactic acid.
Fermented sausages

In lists of nutritional information lactic acid might be included under the term "carbohydrate" (or "carbohydrate by difference") because this often includes everything other than water, protein, fat, ash, and ethanol.^[46] If this is the case then the calculated food energy may use the standard Template:Cvt that is often used for all carbohydrates. But in some cases lactic acid is ignored in the calculation.^[47] The actual energy density of lactic acid is Template:Cvt.^[48]

While not normally found in significant quantities in fruit, lactic acid is the primary organic acid in akebia fruit, making up 2.12% of the juice.^[49]

Separately added

As a food additive it is approved for use in the EU,^[50] United States^[51] and Australia and New Zealand;^[52] it is listed by its INS number 270 or as E number E270. Lactic acid is used as a food preservative, curing agent, and flavoring agent.^[53] It is an ingredient in processed foods and is used as a decontaminant during meat processing.^[54] Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis.^[53] Carbohydrate sources include corn, beets, and cane sugar.^[55]

Forgery

Lactic acid has historically been used to assist with the erasure of inks from official papers to be modified during forgery.^[56]

Cleaning products

Lactic acid is used in some liquid cleaners as a descaling agent for removing hard water deposits such as calcium carbonate.^[57]

References

Template:Reflist

External links

Corn Plastic to the Rescue Template:Webarchive
Lactic Acid: Information and Resources
Lactic Acid Is Not Muscles' Foe, It's Fuel
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Template:Gynecological anti-infectives and antiseptics Template:Lactates Template:Portal bar Template:Authority control

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[lactate-mass-40] Derived from mass values using molar mass of 90.08 g/mol

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@@ Line 1: / Line 1: @@
 {{Short description|Organic acid}}
-{{Use dmy dates|date=July 2018}}
+{{Use dmy dates|date=August 2025}}
 {{chembox
 |Verifiedfields =
@@ Line 11: / Line 11: @@
 |ImageSizeR1 = 130
 |ImageCaption2 = {{sc|L}}-Lactic acid
-|PIN = 2-Hydroxypropanoic acid<ref name=iupac2013>{{cite book | title =  Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = [[Royal Society of Chemistry|The Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 748 | doi = 10.1039/9781849733069-00648 | isbn = 978-0-85404-182-4| chapter = CHAPTER P-6. Applications to Specific Classes of Compounds }}</ref>
+|PIN = 2-Hydroxypropanoic acid<ref name=iupac2013>{{cite book | title =  Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = [[Royal Society of Chemistry|The Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 748 | doi = 10.1039/9781849733069-00648 | isbn = 978-0-85404-182-4 | chapter = CHAPTER P-6. Applications to Specific Classes of Compounds }}</ref>
 |OtherNames = {{ubl|Lactic acid<ref name=iupac2013 />|Milk acid}}
 |Section1 = {{Chembox Identifiers
@@ Line 55: / Line 55: @@
 |Section2 = {{Chembox Properties
 |C=3 | H=6 | O=3
-|Solubility=Miscible<ref name=GESTIS>{{GESTIS|ZVG=13000}}</ref>
+|Solubility= 86.1% w/w at 20°C <BR/> 88.6% w/w  at 25°C
 |MeltingPtC =18
 |BoilingPtC = 122
 |BoilingPt_notes = at 15{{nbsp}}mmHg
-|pKa = 3.86,<ref>{{cite book| vauthors = Dawson RM |display-authors=etal|title=Data for Biochemical Research|location=Oxford|publisher=Clarendon Press|date=1959}}</ref> 15.1<ref>{{cite journal | vauthors = Silva AM, Kong X, Hider RC |title = Determination of the pKa value of the hydroxyl group in the alpha-hydroxycarboxylates citrate, malate and lactate by 13C NMR: implications for metal coordination in biological systems | journal = Biometals | volume = 22 | issue = 5 | pages = 771–8 | date = October 2009 | pmid = 19288211 | doi = 10.1007/s10534-009-9224-5 | s2cid = 11615864 }}</ref>
+|pKa = 3.86,<ref>{{cite book| vauthors = Dawson RM |display-authors=etal |title=Data for Biochemical Research |location=Oxford |publisher=Clarendon Press |date=1959}}</ref> 15.1<ref>{{cite journal | vauthors = Silva AM, Kong X, Hider RC |title = Determination of the pKa value of the hydroxyl group in the alpha-hydroxycarboxylates citrate, malate and lactate by 13C NMR: implications for metal coordination in biological systems | journal = Biometals | volume = 22 | issue = 5 | pages = 771–778 | date = October 2009 | pmid = 19288211 | doi = 10.1007/s10534-009-9224-5 | s2cid = 11615864 }}</ref>
 }}
 |Section3 = {{Chembox Thermochemistry| DeltaHc = 1361.9{{nbsp}}kJ/mol, 325.5{{nbsp}}kcal/mol, 15.1{{nbsp}}kJ/g, 3.61{{nbsp}}kcal/g}}
 |Section4 = {{Chembox Related
-|OtherAnions = Lactate
+|OtherAnions = lactate
 |OtherFunction_label = [[carboxylic acid]]s
-|OtherFunction = {{ubl|[[Acetic acid]]|[[Glycolic acid]]|[[Propionic acid]]|[[3-Hydroxypropanoic acid]]|[[Malonic acid]]|[[Butyric acid]]|[[Hydroxybutyric acid]]}}
+|OtherFunction = {{ubl|[[acetic acid]]|[[glycolic acid]]|[[propionic acid]]|[[3-hydroxypropanoic acid]]|[[malonic acid]]|[[butyric acid]]|[[hydroxybutyric acid]]}}
-|OtherCompounds = {{ubl|[[1-Propanol]]|[[2-Propanol]]|[[Propionaldehyde]]|[[Acrolein]]|[[Sodium lactate]]|[[Ethyl lactate]]}}
+|OtherCompounds = {{ubl|[[1-propanol]]|[[2-propanol]]|[[propionaldehyde]]|[[acrolein]]|[[sodium lactate]]|[[ethyl lactate]]}}
 }}
 |Section5 = {{Chembox Pharmacology
@@ Line 79: / Line 79: @@
 }}
 }}
+'''Lactic acid''' is an [[organic acid]] with the molecular formula '''C<sub>3</sub>H<sub>6</sub>O<sub>3</sub>'''. In its solid state, it is white and [[miscibility|miscible]] with water.<ref name=GESTIS>{{GESTIS|ZVG=13000}}.</ref> When dissolved, it forms a colorless solution. Production includes both artificial synthesis and natural sources. Lactic acid is an [[alpha-hydroxy acid]] (AHA) due to the presence of a [[hydroxyl]] group adjacent to the [[carboxyl]] group. It is a synthetic intermediate in many [[organic synthesis]] industries and in various [[biochemical]] industries. The [[conjugate base]] of lactic acid is called '''lactate''' (or the lactate anion). The name of the derived [[acyl group]] is '''lactoyl'''.
-'''Lactic acid''' is an [[organic acid]]. It has the molecular formula '''C<sub>3</sub>H<sub>6</sub>O<sub>3</sub>'''. It is white in the solid state and it is [[miscibility|miscible]] with water.<ref name=GESTIS/> When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natural sources. Lactic acid is an [[alpha-hydroxy acid]] (AHA) due to the presence of a [[hydroxyl]] group adjacent to the [[carboxyl]] group. It is used as a synthetic intermediate in many [[organic synthesis]] industries and in various [[biochemical]] industries. The [[conjugate base]] of lactic acid is called '''lactate''' (or the lactate anion). The name of the derived [[acyl group]] is '''lactoyl'''.
+In solution, it can ionize by a loss of a proton to produce the lactate [[ion]] {{chem|CH|3|CH(OH)CO|2|−}}, also known as 2-hydroxypropanoate. Compared to [[acetic acid]], its [[Acid dissociation constant|p''K''{{sub|a}}]] is 1 unit less, meaning that lactic acid is ten times more acidic than acetic acid. This higher acidity is the consequence of intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group.
-In solution, it can ionize by a loss of a proton to produce the lactate [[ion]] {{chem|CH|3|CH(OH)CO|2|−}}. Compared to [[acetic acid]], its [[Acid dissociation constant|p''K''{{sub|a}}]] is 1 unit less, meaning lactic acid is ten times more acidic than acetic acid. This higher acidity is the consequence of the intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group.
+Lactic acid is [[chirality (chemistry)|chiral]], consisting of two [[enantiomer]]s. One is known as {{sc|L}}-lactic acid, (''S'')-lactic acid, or (+)-lactic acid, and the other, its mirror image, is {{sc|D}}-lactic acid, (''R'')-lactic acid, or (−)-lactic acid. A mixture of the two in equal amounts is called {{sc|DL}}-lactic acid, or [[racemic]] lactic acid. Lactic acid is [[hygroscopy|hygroscopic]]. {{sc|DL}}-Lactic acid is [[miscible]] with water and with ethanol above its melting point, which is {{cvt|16|-|18|C}}. {{sc|D}}-Lactic acid and {{sc|L}}-lactic acid have a higher melting point. Lactic acid produced by fermentation of milk is often racemic, although certain species of bacteria produce solely {{sc|D}}-lactic acid.<ref>{{Cite web |title=(S)-lactic acid (CHEBI:422) |url=https://www.ebi.ac.uk/chebi/searchId.do?printerFriendlyView=true&locale=null&chebiId=422&viewTermLineage=null&structureView=& |access-date=5 January 2024 |website=www.ebi.ac.uk}}</ref> On the other hand, lactic acid produced by fermentation in animal muscles has the ({{sc|L}}) enantiomer and is sometimes called "sarcolactic" acid, from the Greek {{transliteration|grc|sarx}}, meaning "flesh".
-Lactic acid is [[chirality (chemistry)|chiral]], consisting of two [[enantiomer]]s. One is known as {{sc|L}}-lactic acid, (''S'')-lactic acid, or (+)-lactic acid, and the other, its mirror image, is {{sc|D}}-lactic acid, (''R'')-lactic acid, or (−)-lactic acid. A mixture of the two in equal amounts is called {{sc|DL}}-lactic acid, or [[racemic]] lactic acid. Lactic acid is [[hygroscopy|hygroscopic]]. {{sc|DL}}-Lactic acid is [[miscible]] with water and with ethanol above its melting point, which is about {{cvt|16 to 18|C}}. {{sc|D}}-Lactic acid and {{sc|L}}-lactic acid have a higher melting point. Lactic acid produced by fermentation of milk is often racemic, although certain species of bacteria produce solely {{sc|D}}-lactic acid.<ref>{{Cite web |title=(S)-lactic acid (CHEBI:422) |url=https://www.ebi.ac.uk/chebi/searchId.do?printerFriendlyView=true&locale=null&chebiId=422&viewTermLineage=null&structureView=& |access-date=2024-01-05 |website=www.ebi.ac.uk}}</ref> On the other hand, lactic acid produced by fermentation in animal muscles has the ({{sc|L}}) enantiomer and is sometimes called "sarcolactic" acid, from the Greek {{transliteration|grc|sarx}}, meaning "flesh".
+In animals, {{sc|L}}-lactate is constantly produced from [[pyruvate]] via the [[enzyme]] [[lactate dehydrogenase]] (LDH) in a process of [[fermentation (biochemistry)|fermentation]] during normal [[metabolism]] and [[exercise]].<ref name="Skeletal muscle PGC-1α controls who">{{cite journal | vauthors = Summermatter S, Santos G, Pérez-Schindler J, Handschin C | title = Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 110 | issue = 21 | pages = 8738–8743 | date = May 2013 | pmid = 23650363 | pmc = 3666691 | doi = 10.1073/pnas.1212976110 | bibcode = 2013PNAS..110.8738S | doi-access = free }}</ref> 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 transporter]]s, concentration and isoform of LDH, and oxidative capacity of tissues.<ref name="Skeletal muscle PGC-1α controls who"/> This reaction is reversible and redox-linked: LDH reduces pyruvate to lactate using NADH as an electron donor, simultaneously regenerating [[NAD+|NAD⁺]] required for glycolysis under anaerobic conditions.<ref>{{Citation |last=Farhana |first=Aisha |title=Biochemistry, Lactate Dehydrogenase |date=2025 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK557536/ |access-date=2025-11-11 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32491468 |last2=Lappin |first2=Sarah L.}}</ref> The concentration of [[blood]] lactate is usually {{nowrap|1–2}}{{nbsp}}{{abbrlink|mM|millimolar}} at rest, but can rise to over 20{{nbsp}}mM during intense exertion and as high as 25{{nbsp}}mM afterward.<ref name="LA-UCD">{{cite web | url=http://www.ucdmc.ucdavis.edu/sportsmedicine/resources/lactate_description.html | title=Lactate Profile | publisher=UC Davis Health System, Sports Medicine and Sports Performance | access-date=23 November 2015}}</ref><ref>{{cite journal | vauthors = Goodwin ML, Harris JE, Hernández A, Gladden LB | title = Blood lactate measurements and analysis during exercise: a guide for clinicians | journal = Journal of Diabetes Science and Technology | volume = 1 | issue = 4 | pages = 558–569 | date = July 2007 | pmid = 19885119 | pmc = 2769631 | doi = 10.1177/193229680700100414 }}</ref> In addition to other biological roles, {{sc|L}}-lactic acid is the primary [[endogenous]] [[agonist]] of [[hydroxycarboxylic acid receptor&nbsp;1]] (HCA{{sub|1}}), which is a {{nowrap|[[Gi alpha subunit|G{{sub|i/o}}-coupled]]}} [[G&nbsp;protein-coupled receptor]] (GPCR).<ref name="IUPHAR's comprehensive 2011 review on HCARs">{{cite journal | vauthors = Offermanns S, Colletti SL, Lovenberg TW, Semple G, Wise A, IJzerman AP | title = International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B) | journal = Pharmacological Reviews | volume = 63 | issue = 2 | pages = 269–90 | date = June 2011 | pmid = 21454438 | doi = 10.1124/pr.110.003301 | doi-access = free }}</ref><ref name="IUPHAR-DB HCAR family page">{{cite web | vauthors = Offermanns S, Colletti SL, IJzerman AP, Lovenberg TW, Semple G, Wise A, Waters MG |title=Hydroxycarboxylic acid receptors |url=http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=48 |website=IUPHAR/BPS Guide to Pharmacology |publisher=International Union of Basic and Clinical Pharmacology |access-date=13 July 2018}}</ref>
-In animals, {{sc|L}}-lactate is constantly produced from [[pyruvate]] via the [[enzyme]] [[lactate dehydrogenase]] (LDH) in a process of [[fermentation (biochemistry)|fermentation]] during normal [[metabolism]] and [[exercise]].<ref name="Skeletal muscle PGC-1α controls who">{{cite journal | vauthors = Summermatter S, Santos G, Pérez-Schindler J, Handschin C | title = Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 110 | issue = 21 | pages = 8738–43 | date = May 2013 | pmid = 23650363 | pmc = 3666691 | doi = 10.1073/pnas.1212976110 | bibcode = 2013PNAS..110.8738S | doi-access = free }}</ref> 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 transporter]]s, concentration and isoform of LDH, and oxidative capacity of tissues.<ref name="Skeletal muscle PGC-1α controls who"/> The concentration of [[blood]] lactate is usually {{nowrap|1–2}}{{nbsp}}{{abbrlink|mM|millimolar}} at rest, but can rise to over 20{{nbsp}}mM during intense exertion and as high as 25{{nbsp}}mM afterward.<ref name="LA-UCD">{{cite web | url=http://www.ucdmc.ucdavis.edu/sportsmedicine/resources/lactate_description.html | title=Lactate Profile | publisher=UC Davis Health System, Sports Medicine and Sports Performance | access-date=23 November 2015}}</ref><ref>{{cite journal | vauthors = Goodwin ML, Harris JE, Hernández A, Gladden LB | title = Blood lactate measurements and analysis during exercise: a guide for clinicians | journal = Journal of Diabetes Science and Technology | volume = 1 | issue = 4 | pages = 558–69 | date = July 2007 | pmid = 19885119 | pmc = 2769631 | doi = 10.1177/193229680700100414 }}</ref> In addition to other biological roles, {{sc|L}}-lactic acid is the primary [[endogenous]] [[agonist]] of [[hydroxycarboxylic acid receptor 1]] (HCA{{sub|1}}), which is a {{nowrap|[[Gi alpha subunit|G{{sub|i/o}}-coupled]]}} [[G protein-coupled receptor]] (GPCR).<ref name="IUPHAR's comprehensive 2011 review on HCARs">{{cite journal | vauthors = Offermanns S, Colletti SL, Lovenberg TW, Semple G, Wise A, IJzerman AP | title = International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B) | journal = Pharmacological Reviews | volume = 63 | issue = 2 | pages = 269–90 | date = June 2011 | pmid = 21454438 | doi = 10.1124/pr.110.003301 | doi-access = free }}</ref><ref name="IUPHAR-DB HCAR family page">{{cite web | vauthors = Offermanns S, Colletti SL, IJzerman AP, Lovenberg TW, Semple G, Wise A, Waters MG |title=Hydroxycarboxylic acid receptors |url=http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=48 |website=IUPHAR/BPS Guide to Pharmacology |publisher=International Union of Basic and Clinical Pharmacology |access-date=13 July 2018}}</ref>
+In industry, [[lactic acid fermentation]] is performed by [[lactic acid bacteria]], which convert simple [[carbohydrates]] such as [[glucose]], [[sucrose]], or [[galactose]] to lactic acid. These bacteria can also grow in the [[mouth]]; the [[acid]] they produce is responsible for the [[tooth]] decay known as [[Tooth decay|cavities]].<ref>{{cite journal | vauthors = Badet C, Thebaud NB | title = Ecology of lactobacilli in the oral cavity: a review of literature | journal = The Open Microbiology Journal | volume = 2 | pages = 38–48 | year = 2008 | pmid = 19088910 | pmc = 2593047 | doi =  10.2174/1874285800802010038  |doi-access=free}}</ref><ref>{{cite journal | vauthors = Nascimento MM, Gordan VV, Garvan CW, Browngardt CM, Burne RA | title = Correlations of oral bacterial arginine and urea catabolism with caries experience | journal = Oral Microbiology and Immunology | volume = 24 | issue = 2 | pages = 89–95 | date = April 2009 | pmid = 19239634 | pmc = 2742966 | doi = 10.1111/j.1399-302X.2008.00477.x }}</ref><ref>{{cite journal | vauthors = Aas JA, Griffen AL, Dardis SR, Lee AM, Olsen I, Dewhirst FE, Leys EJ, Paster BJ | title = Bacteria of dental caries in primary and permanent teeth in children and young adults | journal = Journal of Clinical Microbiology | volume = 46 | issue = 4 | pages = 1407–1417 | date = April 2008 | pmid = 18216213 | pmc = 2292933 | doi = 10.1128/JCM.01410-07 }}</ref><ref>{{cite journal | vauthors = Caufield PW, Li Y, Dasanayake A, Saxena D | title = Diversity of lactobacilli in the oral cavities of young women with dental caries | journal = Caries Research | volume = 41 | issue = 1 | pages = 2–8 | year = 2007 | pmid = 17167253 | pmc = 2646165 | doi = 10.1159/000096099 }}</ref> In [[medicine]], lactate is one of the main components of [[lactated Ringer's solution]] and [[Hartmann's solution]]. These [[intravenous]] fluids consist of [[sodium]] and [[potassium]] [[cation]]s along with lactate and [[chloride]] [[anion]]s in solution with distilled [[water]], generally in concentrations [[isotonicity|isotonic]] with [[human]] [[blood]]. It is most commonly used for fluid [[resuscitation]] after blood loss due to [[physical trauma|trauma]], [[surgery]], or [[burn (injury)|burns]].
-In industry, [[lactic acid fermentation]] is performed by [[lactic acid bacteria]], which convert simple [[carbohydrates]] such as [[glucose]], [[sucrose]], or [[galactose]] to lactic acid. These bacteria can also grow in the [[mouth]]; the [[acid]] they produce is responsible for the [[tooth]] decay known as [[Tooth decay|cavities]].<ref>{{cite journal | vauthors = Badet C, Thebaud NB | title = Ecology of lactobacilli in the oral cavity: a review of literature | journal = The Open Microbiology Journal | volume = 2 | pages = 38–48 | year = 2008 | pmid = 19088910 | pmc = 2593047 | doi =  10.2174/1874285800802010038  |doi-access=free}}</ref><ref>{{cite journal | vauthors = Nascimento MM, Gordan VV, Garvan CW, Browngardt CM, Burne RA | title = Correlations of oral bacterial arginine and urea catabolism with caries experience | journal = Oral Microbiology and Immunology | volume = 24 | issue = 2 | pages = 89–95 | date = April 2009 | pmid = 19239634 | pmc = 2742966 | doi = 10.1111/j.1399-302X.2008.00477.x }}</ref><ref>{{cite journal | vauthors = Aas JA, Griffen AL, Dardis SR, Lee AM, Olsen I, Dewhirst FE, Leys EJ, Paster BJ | title = Bacteria of dental caries in primary and permanent teeth in children and young adults | journal = Journal of Clinical Microbiology | volume = 46 | issue = 4 | pages = 1407–17 | date = April 2008 | pmid = 18216213 | pmc = 2292933 | doi = 10.1128/JCM.01410-07 }}</ref><ref>{{cite journal | vauthors = Caufield PW, Li Y, Dasanayake A, Saxena D | title = Diversity of lactobacilli in the oral cavities of young women with dental caries | journal = Caries Research | volume = 41 | issue = 1 | pages = 2–8 | year = 2007 | pmid = 17167253 | pmc = 2646165 | doi = 10.1159/000096099 }}</ref> In [[medicine]], lactate is one of the main components of [[lactated Ringer's solution]] and [[Hartmann's solution]]. These [[intravenous]] fluids consist of [[sodium]] and [[potassium]] [[cation]]s along with lactate and [[chloride]] [[anion]]s in solution with distilled [[water]], generally in concentrations [[isotonicity|isotonic]] with [[human]] [[blood]]. It is most commonly used for fluid [[resuscitation]] after blood loss due to [[physical trauma|trauma]], [[surgery]], or [[burn (injury)|burns]].
+Lactic acid is produced in human tissues when the demand for oxygen is limited by the supply. This occurs during tissue [[ischemia]] when the flow of blood is limited as in sepsis or hemorrhagic shock. It may also occur when demand for oxygen is high, such as with intense exercise. The process of [[lactic acidosis]] produces lactic acid, which results in an [[wikt:oxygen debt|oxygen debt]], which can be resolved or repaid when tissue oxygenation improves.<ref>{{Cite journal |last1=Achanti |first1=Anand |last2=Szerlip |first2=Harold M. |date=1 January 2023 |title=Acid-Base Disorders in the Critically Ill Patient |journal=Clin J Am Soc Nephrol |language=en |volume=18 |issue=1 |pages=102–112 |doi=10.2215/CJN.04500422 |issn=1555-9041 |pmc=10101555 |pmid=35998977}}</ref>
-Lactic acid is produced in human tissues when the demand for oxygen is limited by the supply. This occurs during tissue [[ischemia]] when the flow of blood is limited as in sepsis or hemorrhagic shock. It may also occur when demand for oxygen is high such as with intense exercise. The process of [[lactic acidosis]] produces lactic acid which results in an [[wikt:oxygen debt|oxygen debt]] which can be resolved or repaid when tissue oxygenation improves.<ref>{{Cite journal |last1=Achanti |first1=Anand |last2=Szerlip |first2=Harold M. |date=1 January 2023 |title=Acid-Base Disorders in the Critically Ill Patient |journal=Clin J Am Soc Nephrol |language=en |volume=18 |issue=1 |pages=102–112 |doi=10.2215/CJN.04500422 |issn=1555-9041 |pmc=10101555 |pmid=35998977}}</ref>
 ==History==
-Swedish chemist [[Carl Wilhelm Scheele]] was the first person to isolate lactic acid in 1780 from sour [[milk]].<ref name="Parks">{{cite journal|doi=10.1146/annurev-cancerbio-030419-033556|title=Lactate and Acidity in the Cancer Microenvironment|year=2020|last1=Parks|first1=Scott K.|last2=Mueller-Klieser|first2=Wolfgang|last3=Pouysségur|first3=Jacques|journal=Annual Review of Cancer Biology|volume=4|pages=141–158|doi-access=free}}</ref> The name reflects the ''[[wikt:lact-#Prefix|lact-]]'' combining form derived from the Latin word {{lang|la|[[wikt:lac#Latin|lac]]}}, meaning "milk". In 1808, [[Jöns Jacob Berzelius]] discovered that lactic acid (actually {{sc|L}}-lactate) is also produced in [[muscle]]s during exertion.<ref>{{Cite web|last=Roth|first=Stephen M. | name-list-style = vanc |title=Why does lactic acid build up in muscles? And why does it cause soreness?|website=[[Scientific American]] |url=https://www.scientificamerican.com/article/why-does-lactic-acid-buil/|access-date=23 January 2006}}</ref> Its structure was established by [[Johannes Wislicenus]] in 1873.
+Swedish chemist [[Carl Wilhelm Scheele]] was the first person to isolate lactic acid in 1780 from sour [[milk]].<ref name="Parks">{{cite journal |doi=10.1146/annurev-cancerbio-030419-033556 |title=Lactate and Acidity in the Cancer Microenvironment |year=2020 |last1=Parks |first1=Scott K. |last2=Mueller-Klieser |first2=Wolfgang |last3=Pouysségur |first3=Jacques |journal=Annual Review of Cancer Biology |volume=4 |pages=141–158 |doi-access=free}}</ref> The name reflects the ''[[wikt:lact-#Prefix|lact-]]'' combining form derived from the Latin word {{lang|la|[[wikt:lac#Latin|lac]]}}, meaning "milk". In 1808, [[Jöns Jacob Berzelius]] discovered that lactic acid (actually {{sc|L}}-lactate) is also produced in [[muscle]]s during exertion.<ref>{{Cite web |last=Roth |first=Stephen M. |name-list-style = vanc |title=Why does lactic acid build up in muscles? And why does it cause soreness? |website=[[Scientific American]] |url=https://www.scientificamerican.com/article/why-does-lactic-acid-buil/ |access-date=23 January 2006}}</ref> Its structure was established by [[Johannes Wislicenus]] in 1873.
 In 1856, the role of ''[[Lactobacillus]]'' in the synthesis of lactic acid was discovered by [[Louis Pasteur]]. This pathway was used commercially by the German [[pharmacy]] [[Boehringer Ingelheim]] in 1895.{{cn|date=May 2024}}
-In 2006, global production of lactic acid reached 275,000 tonnes with an average annual growth of 10%.<ref>{{cite web|url=http://www.nnfcc.co.uk/publications/nnfcc-renewable-chemicals-factsheet-lactic-acid|title=NNFCC Renewable Chemicals Factsheet: Lactic Acid|publisher=NNFCC}}</ref>
+Due to a combination of geographic and infrastructural factors, the [[Soviet Union]], as well as several other members of the [[Warsaw Pact]], experienced chronic shortages of [[citric acid|citric]] and [[malic acid]], among others.{{cn|date=August 2025}} In order to combat this issue, the [[Narkomzem]] (Soviet Ministry of Agriculture) invested heavily in the development of suitable lactobacillus strains, which were able to produce lactic acid with relatively high efficiency from crude molasses feedstock.<ref>{{Cite journal |date=7 September 1983 |title=SU 1 039 964 A1 |url=https://patenton.ru/patent/SU1039964A1 |url-status=live |archive-url=https://web.archive.org/web/20250713050213/https://patenton.ru/patent/SU1039964A1 |archive-date=13 July 2025 |access-date=13 July 2025 |website=patenton.ru}}</ref> Despite synthetic citric acid being produced in some quantities across the Warsaw Pact, it proved far more difficult to purify, leading to lactic acid being, on average, a quarter of the cost of citric acid. The continued use of lactic acid in some [[Eastern European]] and [[Central Asian]] food production in the modern day, in favor of the more common citric or malic acids, lends it a distinctive flavor.{{cn|date=August 2025}}
+Global demand for lactic acid continues to expand, with an estimated annual growth rate of 5–8% driven by the increasing use of biodegradable plastics, green solvents, and pharmaceutical intermediates. Worldwide production exceeded 1.5 million tonnes by the early 2020s, up from roughly 275,000 tonnes in 2006, and is projected to keep rising as biobased materials replace petroleum-derived products.<ref>{{cite web |title=NNFCC Renewable Chemicals Factsheet: Lactic Acid |url=http://www.nnfcc.co.uk/publications/nnfcc-renewable-chemicals-factsheet-lactic-acid |url-status=dead |archive-url=https://web.archive.org/web/20120904213907/http://www.nnfcc.co.uk/publications/nnfcc-renewable-chemicals-factsheet-lactic-acid |archive-date=4 September 2012 |access-date=16 February 2011 |publisher=NNFCC}}</ref> Major producers include [[NatureWorks LLC]], Purac, Galactic, and several Chinese manufacturers. NatureWorks operates one of the world’s largest [[polylactic acid]] (PLA) facilities in [[Blair, Nebraska]], with a production capacity of about 140,000 tonnes per year, supplying feedstock for a wide range of [[Biodegradable Packaging for Environment|biodegradable packaging]] and fiber applications.<ref name="maar">{{Cite journal |last=Abdel-Rahman |first=Mohamed Ali |last2=Tashiro |first2=Yukihiro |last3=Sonomoto |first3=Kenji |date=November 2013 |title=Recent advances in lactic acid production by microbial fermentation processes |url=https://pubmed.ncbi.nlm.nih.gov/23624242 |journal=Biotechnology Advances |volume=31 |issue=6 |pages=877–902 |doi=10.1016/j.biotechadv.2013.04.002 |issn=1873-1899 |pmid=23624242}}</ref>
 ==Production==
-Lactic acid is produced industrially by bacterial [[fermentation]] of [[carbohydrate]]s, or by chemical synthesis from [[acetaldehyde]].<ref name=benn>H. Benninga (1990): "A History of Lactic Acid Making: A Chapter in the History of Biotechnology". Volume 11 of ''Chemists and Chemistry''.  Springer, {{ISBN|0792306252}}, 9780792306252</ref> {{As of|2009}}, lactic acid was produced predominantly (70–90%)<ref>{{Cite book|title=Technische Biopolymere|last=Endres|first=Hans-Josef | name-list-style = vanc |publisher=Hanser-Verlag|year=2009|isbn=978-3-446-41683-3|location=München|pages=103}}</ref> by fermentation. Production of racemic lactic acid consisting of a 1:1 mixture of {{sc|D}} and {{sc|L}} stereoisomers, or of mixtures with up to 99.9% {{sc|L}}-lactic acid, is possible by microbial fermentation. Industrial scale production of {{sc|D}}-lactic acid by fermentation is possible, but much more challenging.{{cn|date=May 2024}}
+Lactic acid is produced industrially by bacterial [[fermentation]] of [[carbohydrate]]s, or by chemical synthesis from [[acetaldehyde]].<ref name=benn>H. Benninga (1990): "A History of Lactic Acid Making: A Chapter in the History of Biotechnology". Volume 11 of ''Chemists and Chemistry''.  Springer, {{ISBN|0792306252}}, 9780792306252</ref> {{As of|2009}}, lactic acid was produced predominantly (70–90%)<ref>{{Cite book |title=Technische Biopolymere |last=Endres |first=Hans-Josef |name-list-style = vanc |publisher=Hanser-Verlag |year=2009 |isbn=978-3-446-41683-3 |location=München |pages=103}}</ref> by fermentation. Production of racemic lactic acid consisting of a 1:1 mixture of {{sc|D}} and {{sc|L}} stereoisomers, or of mixtures with up to 99.9% {{sc|L}}-lactic acid, is possible by microbial fermentation. Industrial production of the D-lactic acid enantiomer is technically more challenging because most naturally occurring lactic acid bacteria preferentially produce the L-form; obtaining high optical purity of D-lactic acid therefore requires [[Genetic engineering|genetically engineered]] microorganisms or specific D-lactate dehydrogenases.<ref name="maar"/>
 ===Fermentative production===
 [[Fermented milk products]] are obtained industrially by fermentation of [[milk]] or [[whey]] by ''Lactobacillus'' bacteria: ''[[Lactobacillus acidophilus]]'', ''[[Lacticaseibacillus casei]]'' (''Lactobacillus casei''), [[Lactobacillus delbrueckii subsp. bulgaricus|''Lactobacillus delbrueckii'' subsp. ''bulgaricus'']] (''Lactobacillus bulgaricus''), ''[[Lactobacillus helveticus]]'', ''[[Lactococcus lactis]]'' ,'' [[Bacillus amyloliquefaciens]]'', and [[Streptococcus salivarius subsp. thermophilus|''Streptococcus salivarius'' subsp. ''thermophilus'']] (''Streptococcus thermophilus'').{{cn|date=May 2024}}
-As a starting material for industrial production of lactic acid, almost any carbohydrate source containing {{chem|link=Pentose|C|5}} (Pentose sugar) and {{chem|link=Hexose|C|6}} (Hexose sugar) can be used. Pure sucrose, glucose from starch, raw sugar, and beet juice are frequently used.<ref>{{cite book|last1=Groot|first1=Wim|last2=van Krieken|first2=Jan|last3=Slekersl|first3=Olav|last4=de Vos|first4=Sicco|editor1-last=Auras|editor1-first=Rafael|editor2-last=Lim|editor2-first=Long-Tak|editor3-last=Selke|editor3-first=Susan E. M.|editor4-last=Tsuji|editor4-first=Hideto | name-list-style = vanc |contribution=Chemistry and production of lactic acid, lactide and poly(lactic acid) |title=Poly(Lactic acid)|publisher=Wiley|location=Hoboken|isbn=978-0-470-29366-9|page=3|date=2010-10-19}}</ref> Lactic acid producing bacteria can be divided in two classes: homofermentative bacteria like ''Lactobacillus casei'' and ''Lactococcus lactis'', producing two moles of lactate from one mole of glucose, and heterofermentative species producing one mole of lactate from one mole of glucose as well as [[carbon dioxide]] and [[acetic acid]]/[[ethanol]].<ref>{{cite book|last1=König|first1=Helmut|last2=Fröhlich|first2=Jürgen | name-list-style = vanc |title=Lactic acid bacteria in Biology of Microorganisms on Grapes, in Must and in Wine|date=2009|publisher=Springer-Verlag|isbn=978-3-540-85462-3|page=3}}</ref>
+As a starting material for industrial production of lactic acid, almost any carbohydrate source containing {{chem|link=Pentose|C|5}} (pentose sugar) and {{chem|link=Hexose|C|6}} (hexose sugar) can be used. Pure [[sucrose]], [[glucose]] from [[starch]], raw sugar, and beet juice are frequently used.<ref>{{cite book |last1=Groot |first1=Wim |last2=van Krieken |first2=Jan |last3=Slekersl |first3=Olav |last4=de Vos |first4=Sicco |editor1-last=Auras |editor1-first=Rafael |editor2-last=Lim |editor2-first=Long-Tak |editor3-last=Selke |editor3-first=Susan E. M. |editor4-last=Tsuji |editor4-first=Hideto |name-list-style = vanc |contribution=Chemistry and production of lactic acid, lactide and poly(lactic acid) |title=Poly(Lactic acid) |publisher=Wiley |location=Hoboken |isbn=978-0-470-29366-9 |page=3 |date=19 October 2010}}</ref> Lactic acid producing bacteria can be divided in two classes: homofermentative bacteria like ''Lactobacillus casei'' and ''Lactococcus lactis'', producing two moles of lactate from one mole of glucose, and heterofermentative species, producing one mole of lactate from one mole of glucose, as well as [[carbon dioxide]] and [[acetic acid]]/[[ethanol]].<ref>{{cite book |last1=König |first1=Helmut |last2=Fröhlich |first2=Jürgen |name-list-style = vanc |title=Lactic acid bacteria in Biology of Microorganisms on Grapes, in Must and in Wine |date=2009 |publisher=Springer-Verlag |isbn=978-3-540-85462-3 |page=3}}</ref>
 ===Chemical production===
-Racemic lactic acid is synthesized industrially by reacting [[acetaldehyde]] with [[hydrogen cyanide]] and hydrolysing the resultant [[lactonitrile]]. When [[hydrolysis]] is performed by [[hydrochloric acid]], [[ammonium chloride]] forms as a by-product; the Japanese company Musashino is one of the last big manufacturers of lactic acid by this route.<ref>{{Ullmann|last1=Westhoff|first1=Gerrit|last2=Starr|first2=John N.| title=Lactic Acids|year=2012|doi=10.1002/14356007.a15_097.pub3|isbn=9783527306732}}</ref> Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials ([[vinyl acetate]], [[glycerol]], etc.) by application of catalytic procedures.<ref>{{cite journal|last1=Shuklov|first1=Ivan A.|last2=Dubrovina|first2=Natalia V.|last3=Kühlein|first3=Klaus|last4=Börner|first4=Armin | name-list-style = vanc |title=Chemo-Catalyzed Pathways to Lactic Acid and Lactates|journal=Advanced Synthesis and Catalysis|date=2016|volume=358|issue=24|pages=3910–3931|doi=10.1002/adsc.201600768}}</ref>
+Racemic lactic acid is synthesized industrially by reacting [[acetaldehyde]] with [[hydrogen cyanide]] and hydrolysing the resultant [[lactonitrile]]. When [[hydrolysis]] is performed by [[hydrochloric acid]], [[ammonium chloride]] forms as a by-product; the Japanese company Musashino is one of the last big manufacturers of lactic acid by this route.<ref>{{Ullmann |last1=Westhoff |first1=Gerrit |last2=Starr |first2=John N. |title=Lactic Acids |year=2012 |doi=10.1002/14356007.a15_097.pub3 |isbn=9783527306732}}</ref> Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials ([[vinyl acetate]], [[glycerol]], etc.) by application of catalytic procedures.<ref>{{cite journal |last1=Shuklov |first1=Ivan A. |last2=Dubrovina |first2=Natalia V. |last3=Kühlein |first3=Klaus |last4=Börner |first4=Armin |name-list-style = vanc |title=Chemo-Catalyzed Pathways to Lactic Acid and Lactates |journal=Advanced Synthesis and Catalysis |date=2016 |volume=358 |issue=24 |pages=3910–3931 |doi=10.1002/adsc.201600768}}</ref>
 ==Biology==
@@ Line 148: / Line 149: @@
 The resulting increase in acidity persists until the excess lactate and protons are converted back to pyruvate, and then to glucose for later use, or to {{chem2|CO2}} and water for the production of ATP.<ref name="Ferguson 2018" />
+=== pH Regulation ===
+Lactate production and export contribute significantly to intracellular pH regulation in metabolically active tissues. In [[skeletal muscle]], accumulation of lactic acid lowers intracellular pH, and [[Monocarboxylate transporter|monocarboxylate transporters]] facilitate the efflux of both lactate and H⁺, thereby helping maintain [[Acid–base homeostasis|acid-base homeostasis]] and delaying fatigue.<ref>{{Cite journal |last=Juel |first=C. |date=March 1996 |title=Lactate/proton co‐transport in skeletal muscle: regulation and importance for pH homeostasis |url=https://doi.org/10.1046/j.1365-201x.1996.206000.x |journal=Acta Physiologica Scandinavica |volume=156 |issue=3 |pages=369–374 |doi=10.1046/j.1365-201x.1996.206000.x |issn=0001-6772|url-access=subscription }}</ref>
 === Neural tissue energy source ===
-Although [[glucose]] is usually assumed to be the main energy source for living tissues, there is evidence that lactate, in preference to  glucose, is preferentially metabolized by [[neuron]]s in the [[brain]]s of several [[mammalian]] species that include [[mouse|mice]], [[rat]]s, and [[human]]s.<ref name=zilberter2010/><ref>{{cite journal | vauthors = Wyss MT, Jolivet R, Buck A, Magistretti PJ, Weber B | title = In vivo evidence for lactate as a neuronal energy source | journal = The Journal of Neuroscience | volume = 31 | issue = 20 | pages = 7477–85 | date = May 2011 | pmid = 21593331 | pmc = 6622597 | doi = 10.1523/JNEUROSCI.0415-11.2011 | url = http://www.zora.uzh.ch/55080/1/Wyss_Weber_J_Neuroscience%282011%29.pdf }}</ref><ref name="Ferguson 2018" />  According to the [[lactate shuttle|lactate-shuttle hypothesis]], [[glia]]l cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons.<ref>{{cite journal | vauthors = Gladden LB | title = Lactate metabolism: a new paradigm for the third millennium | journal = The Journal of Physiology | volume = 558 | issue = Pt 1 | pages = 5–30 | date = July 2004 | pmid = 15131240 | pmc = 1664920 | doi = 10.1113/jphysiol.2003.058701 }}</ref><ref>{{cite journal | vauthors = Pellerin L, Bouzier-Sore AK, Aubert A, Serres S, Merle M, Costalat R, Magistretti PJ | title = Activity-dependent regulation of energy metabolism by astrocytes: an update | journal = Glia | volume = 55 | issue = 12 | pages = 1251–62 | date = September 2007 | pmid = 17659524 | doi = 10.1002/glia.20528 | s2cid = 18780083 }}</ref> Because of this local metabolic activity of glial cells, the [[extracellular fluid]] immediately surrounding neurons strongly differs in composition from the [[blood]] or [[cerebrospinal fluid]], being much richer with lactate, as was found in [[microdialysis]] studies.<ref name=zilberter2010>{{cite journal | vauthors = Zilberter Y, Zilberter T, Bregestovski P | title = Neuronal activity in vitro and the in vivo reality: the role of energy homeostasis | journal = Trends in Pharmacological Sciences | volume = 31 | issue = 9 | pages = 394–401 | date = September 2010 | pmid = 20633934 | doi = 10.1016/j.tips.2010.06.005 }}</ref>
+Although [[glucose]] is usually assumed to be the main energy source for living tissues, there is evidence that lactate, in preference to  glucose, is preferentially metabolized by [[neuron]]s in the [[brain]]s of several [[mammalian]] species that include [[mouse|mice]], [[rat]]s, and [[human]]s.<ref name=zilberter2010/><ref>{{cite journal | vauthors = Wyss MT, Jolivet R, Buck A, Magistretti PJ, Weber B | title = In vivo evidence for lactate as a neuronal energy source | journal = The Journal of Neuroscience | volume = 31 | issue = 20 | pages = 7477–85 | date = May 2011 | pmid = 21593331 | pmc = 6622597 | doi = 10.1523/JNEUROSCI.0415-11.2011 | url = http://www.zora.uzh.ch/55080/1/Wyss_Weber_J_Neuroscience%282011%29.pdf }}</ref><ref name="Ferguson 2018" />  According to the [[lactate shuttle|lactate-shuttle hypothesis]], [[glia]]l cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons.<ref>{{cite journal | vauthors = Gladden LB | title = Lactate metabolism: a new paradigm for the third millennium | journal = The Journal of Physiology | volume = 558 | issue = Pt 1 | pages = 5–30 | date = July 2004 | pmid = 15131240 | pmc = 1664920 | doi = 10.1113/jphysiol.2003.058701 }}</ref><ref>{{cite journal | vauthors = Pellerin L, Bouzier-Sore AK, Aubert A, Serres S, Merle M, Costalat R, Magistretti PJ | title = Activity-dependent regulation of energy metabolism by astrocytes: an update | journal = Glia | volume = 55 | issue = 12 | pages = 1251–62 | date = September 2007 | pmid = 17659524 | doi = 10.1002/glia.20528 | s2cid = 18780083 | url = https://infoscience.epfl.ch/handle/20.500.14299/45347 }}</ref> Because of this local metabolic activity of glial cells, the [[extracellular fluid]] immediately surrounding neurons strongly differs in composition from the [[blood]] or [[cerebrospinal fluid]], being much richer with lactate, as was found in [[microdialysis]] studies.<ref name=zilberter2010>{{cite journal | vauthors = Zilberter Y, Zilberter T, Bregestovski P | title = Neuronal activity in vitro and the in vivo reality: the role of energy homeostasis | journal = Trends in Pharmacological Sciences | volume = 31 | issue = 9 | pages = 394–401 | date = September 2010 | pmid = 20633934 | doi = 10.1016/j.tips.2010.06.005 }}</ref>
 === Brain development metabolism ===
@@ Line 185: / Line 189: @@
 == Uses ==
+In 2023, lactate was the 289th most commonly prescribed medication in the United States, with more than 500,000 prescriptions.<ref>{{cite web | title=The Top 300 of 2023 | url=https://clincalc.com/DrugStats/Top300Drugs.aspx | website=ClinCalc | access-date=17 August 2025 | archive-date=17 August 2025 | archive-url=https://web.archive.org/web/20250817043812/https://clincalc.com/DrugStats/Top300Drugs.aspx | url-status=live }}</ref><ref>{{cite web | title = Lactate Drug Usage Statistics, United States, 2014 - 2023 | website = ClinCalc | url = https://clincalc.com/DrugStats/Drugs/Lactate | access-date = 17 August 2025 }}</ref>
 === Polymer precursor ===
 {{Main article|polylactic acid}}
 Two molecules of lactic acid can be dehydrated to the [[lactone]] [[lactide]].  In the presence of [[catalysts]] lactide polymerize to either atactic or [[syndiotactic]] [[polylactic acid|polylactide]] (PLA), which are [[biodegradable]] [[polyester]]s. PLA is an example of a plastic that is not derived from [[petrochemical]]s.
@@ Line 197: / Line 204: @@
 ==== Fermented food ====
 {{main|Lactic acid fermentation#Applications}}
 Lactic acid is found in many fermented foods.
 * Sour [[milk]] products, such as [[kumis]], [[Strained yogurt|laban]], [[yogurt]], [[kefir]], and some [[cottage cheese]]s, derive their flavor from lactic acid. The [[casein]] in fermented milk is coagulated (curdled) by lactic acid.
@@ Line 205: / Line 213: @@
 * [[Fermented sausage]]s
-In lists of [[nutritional information]] lactic acid might be included under the term "carbohydrate" (or "carbohydrate by difference") because this often includes everything other than water, protein, fat, ash, and ethanol.<ref>{{cite web|title=USDA National Nutrient Database for Standard Reference, Release 28 (2015) Documentation and User Guide|url=http://www.ars.usda.gov/sp2UserFiles/Place/80400525/Data/SR/SR28/sr28_doc.pdf|page=13|date=2015}}</ref> If this is the case then the calculated [[food energy]] may use the standard {{convert|4|kcal}} per gram that is often used for all carbohydrates. But in some cases lactic acid is ignored in the calculation.<ref>For example, in [https://web.archive.org/web/20181116194139/https://ndb.nal.usda.gov/ndb/foods/show/105?n1=%7BQv%3D1%7D this USDA database entry for yoghurt] the food energy is calculated using given coefficients for carbohydrate, fat, and protein. (One must click on "Full report" to see the coefficients.) The calculated value is based on 4.66 grams of carbohydrate, which is exactly equal to the sugars.</ref> The actual energy density of lactic acid is {{convert|3.62|kcal}} per g.<ref name = "FAOSouthgate">{{cite book |last1=Greenfield |first1=Heather |last2=Southgate |first2=D.A.T.  | name-list-style = vanc |date=2003 |title=Food Composition Data: Production, Management and Use |location=Rome |publisher=[[FAO]] |page=146 |isbn=9789251049495 }}</ref>
+In lists of [[nutritional information]] lactic acid might be included under the term "carbohydrate" (or "carbohydrate by difference") because this often includes everything other than water, protein, fat, ash, and ethanol.<ref>{{cite web|title=USDA National Nutrient Database for Standard Reference, Release 28 (2015) Documentation and User Guide|url=https://www.ars.usda.gov/ARSUserFiles/80400525/Data/SR/SR28/sr28_doc.pdf|page=13|date=2015}}</ref> If this is the case then the calculated [[food energy]] may use the standard {{cvt|4|kcal/g}} that is often used for all carbohydrates. But in some cases lactic acid is ignored in the calculation.<ref>For example, in [https://web.archive.org/web/20181116194139/https://ndb.nal.usda.gov/ndb/foods/show/105?n1=%7BQv%3D1%7D this USDA database entry for yoghurt] the food energy is calculated using given coefficients for carbohydrate, fat, and protein. (One must click on "Full report" to see the coefficients.) The calculated value is based on 4.66 grams of carbohydrate, which is exactly equal to the sugars.</ref> The actual energy density of lactic acid is {{cvt|3.62|kcal/g}}.<ref name = "FAOSouthgate">{{cite book |last1=Greenfield |first1=Heather |last2=Southgate |first2=D.A.T.  | name-list-style = vanc |date=2003 |title=Food Composition Data: Production, Management and Use |location=Rome |publisher=[[FAO]] |page=146 |isbn=9789251049495 }}</ref>
 While not normally found in significant quantities in fruit, lactic acid is the primary organic acid in [[akebia]] fruit, making up 2.12% of the juice.<ref>{{cite journal |author=Li |first1=Li |last2=Yao |first2=Xiaohong |last3=Zhong |first3=Caihong |last4=Chen |first4=Xuzhong |date=January 2010 |title=Akebia: A Potential New Fruit Crop in China |journal=HortScience |volume=45 |pages=4–10 |doi=10.21273/HORTSCI.45.1.4 |doi-access=free |number=1}}</ref>
@@ Line 216: / Line 224: @@
 === Cleaning products ===
 Lactic acid is used in some liquid cleaners as a [[descaling agent]]  for removing [[hard water]] deposits such as [[calcium carbonate]].<ref>{{cite book | title = Sustainable Agriculture Reviews 34: Date Palm for Food Medicine and the Environment | url = https://books.google.com/books?id=gBCTDwAAQBAJ | last1 = Naushad | first1 = Mu. | last2 = Lichtfouse | first2 = Eric | date = 2019 | publisher = Springer | page = 162| isbn=978-3-030-11345-2 }}</ref>
 == See also ==
@@ Line 230: / Line 238: @@
 == References ==
-{{Reflist|30em}}
+{{Reflist}}
 == External links ==
@@ Line 236: / Line 244: @@
 * [http://www.webmd.com/a-to-z-guides/lactic-acid Lactic Acid: Information and Resources]
 * [https://www.nytimes.com/2006/05/16/health/nutrition/16run.html Lactic Acid Is Not Muscles' Foe, It's Fuel]
-* {{cite web |first=Matt |last=Fitzgerald  | name-list-style = vanc |date=January 26, 2010 |title=The Lactic Acid Myths |work=Competitor Running |url=http://running.competitor.com/2010/01/training/the-lactic-acid-myths_7938|archive-url=https://web.archive.org/web/20180825120642/http://running.competitor.com/2010/01/training/the-lactic-acid-myths_7938|archive-date=25 August 2018 |url-status=dead}}
+* {{cite web |first=Matt |last=Fitzgerald  | name-list-style = vanc |date=26 January 2010 |title=The Lactic Acid Myths |work=Competitor Running |url=http://running.competitor.com/2010/01/training/the-lactic-acid-myths_7938|archive-url=https://web.archive.org/web/20180825120642/http://running.competitor.com/2010/01/training/the-lactic-acid-myths_7938|archive-date=25 August 2018 |url-status=dead}}
 {{Gynecological anti-infectives and antiseptics}}
 {{Lactates}}
+{{Portal bar | Medicine}}
 {{Authority control}}
 [[Category:Food acidity regulators]]
-[[Category:Alpha hydroxy acids]]
+[[Category:Alpha hydroxycarboxylic acids]]
 [[Category:Exercise physiology]]
 [[Category:Preservatives]]
 [[Category:Propionic acids]]
 [[Category:E-number additives]]

Lactic acid: Difference between revisions

Latest revision as of 23:26, 19 November 2025

Contents

History

Production

Fermentative production

Chemical production

Biology

Molecular biology

Metabolism and exercise

pH Regulation

Neural tissue energy source

Brain development metabolism

Blood testing

Uses

Polymer precursor

Pharmaceutical and cosmetic applications

Foods

Fermented food

Separately added

Forgery

Cleaning products

See also

References

External links

Navigation menu

Lactic acid: Difference between revisions

Latest revision as of 23:26, 19 November 2025

History

Production

Fermentative production

Chemical production

Biology

Molecular biology

Metabolism and exercise

pH Regulation

Neural tissue energy source

Brain development metabolism

Blood testing

Uses

Polymer precursor

Pharmaceutical and cosmetic applications

Foods

Fermented food

Separately added

Forgery

Cleaning products

See also

References

External links

Navigation menu

Search