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Lactic acid is an
organic acid An organic acid is an with ic properties. The most common organic acids are the s, whose acidity is associated with their  –COOH. s, containing the group –SO2OH, are relatively stronger acids. Alcohols, with , can act as acids but t ...
. It has a molecular formula CH3CH(OH)COOH. It is white in the solid state and it is
miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...
with water. 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 α-Hydroxy acids, or alpha hydroxy acids (AHAs), are a class of chemical compounds that consist of a carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of ...
(AHA) due to the presence of a
hydroxyl A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the ...

hydroxyl
group adjacent to the
carboxyl A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...

carboxyl
group. It is used as a synthetic intermediate in many
organic synthesis Organic synthesis is a special branch of chemical synthesis As a topic of , chemical synthesis (or combination) is the artificial execution of s to obtain one or several s. This occurs by and chemical manipulations usually involving one or mo ...

organic synthesis
industries and in various
biochemical Biochemistry or biological chemistry, is the study of chemical process In a scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. L ...
industries. The
conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory The Brønsted–Lowry theory (also called proton theory of acids and bases) is an acid–base reaction An acid–base reaction is a chemical reaction A chemical reactio ...
of lactic acid is called lactate. In solution, it can ionize by loss of a proton to produce the lactate
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
. Compared to
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
, its p''K''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
chiral Chirality is a property of important in several branches of science. The word ''chirality'' is derived from the (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from its ; that is, i ...
, consisting of two
enantiomer In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they und ...
s. One is known as -lactic acid, (''S'')-lactic acid, or (+)-lactic acid, and the other, its mirror image, is -lactic acid, (''R'')-lactic acid, or (−)-lactic acid. A mixture of the two in equal amounts is called -lactic acid, or
racemic In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...
lactic acid. Lactic acid is
hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water m ...
. -Lactic acid is
miscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...
with water and with ethanol above its melting point, which is about 16 to 18 °C. -Lactic acid and -lactic acid have a higher melting point. Lactic acid produced by fermentation of milk is often racemic, although certain species of bacteria produce solely -lactic acid. On the other hand, lactic acid produced by anaerobic respiration in animal muscles has the () enantiomer and is sometimes called "sarcolactic" acid, from the Greek "sarx" for flesh. In animals, -lactate is constantly produced from
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

pyruvate
via the
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates in ...

enzyme
lactate dehydrogenase Lactate dehydrogenase (LDH or LD) is an enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules kno ...
(LDH) in a process of
fermentation Fermentation is a metabolism, metabolic process that produces chemical changes in organic Substrate (chemistry), substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in ...
during normal
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
and
exercise Exercise is any bodily activity that enhances or maintains physical fitness Physical fitness is a state of health Health is a state of physical, mental and social well-being Well-being, also known as ''wellness'', ''prudential value ...

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 Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
lactate is usually   at rest, but can rise to over 20 mM during intense exertion and as high as 25 mM afterward. In addition to other biological roles, -lactic acid is the primary
endogenous Endogenous substances and processes are those that originate from within a system such as an organism, Tissue (biology), tissue, or Cell (biology), cell. Endogenous substances and processes contrast with exogenous ones, such as Drug, drugs, which ...
agonist An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. In contrast, an antagonist blocks the action of the agonist, while an inverse agonist causes an action opposite to that of the agonist ...

agonist
of hydroxycarboxylic acid receptor 1 (HCA1), which is a
G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of protein family, evolutionar ...
(GPCR). In industry,
lactic acid fermentation One isomer of lactic acid Lactic acid fermentation is a metabolic process by which glucose or other hexose, six-carbon sugars (also, disaccharides of six-carbon sugars, e.g. sucrose or lactose) are converted into cellular energy and the metabolit ...

lactic acid fermentation
is performed by
lactic acid bacteria Lactobacillales are an order of gram-positive, GC-content, low-GC, acid-tolerant, generally nonsporulating, Aerotolerant anaerobe, nonrespiring, either rod-shaped (bacillus (shape), bacilli) or spherical (cocci) bacteria that share common metab ...
, which convert simple
carbohydrates is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar Sugar is the generic name for sweet-tasting, soluble carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galacto ...
such as
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
,
sucrose Sucrose is a type of sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosacchari ...

sucrose
, or
galactose Galactose (, '' galacto-'' + ''-ose The suffix In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. Th ...
to lactic acid. These bacteria can also grow in the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
; the
acid An acid is a or capable of donating a (hydrogen ion H+) (a ), or, alternatively, capable of forming a with an (a ). The first category of acids are the proton donors, or s. In the special case of , proton donors form the H3O+ and are ...
they produce is responsible for the
tooth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. ...

tooth
decay known as
caries Tooth decay, also known as dental caries or cavities, is the breakdown of teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the ...
. In
medicine Medicine is the science Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity, awareness, or understanding of someone or something, such as facts ( descriptive knowledge), skills (proced ...

medicine
, lactate is one of the main components of
lactated Ringer's solution Ringer's lactate solution (RL), also known as sodium lactate solution and Hartmann's solution, is a mixture of sodium chloride, sodium lactate, potassium chloride, and calcium chloride in water. It is used for replacing fluids and electrolytes in ...
and Hartmann's solution. These
intravenous Intravenous therapy (abbreviated as IV therapy) is a medical technique that delivers fluids, medications and nutrition directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrition ...
fluids consist of
sodium Sodium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

sodium
and
potassium Potassium is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, b ...

potassium
cation An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are u ...
s along with lactate and
chloride The chloride ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects th ...

chloride
anion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
s in solution with distilled
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
, generally in concentrations isotonic with
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human
blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
. It is most commonly used for fluid
resuscitation Resuscitation is the process of correcting physiological disorder A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any immediate extern ...
after blood loss due to
trauma Trauma most often refers to: *Major trauma, in physical medicine, severe physical injury caused by an external source *Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic injur ...
,
surgery Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical or dental specialty that uses operative manual and instrumental techniques on a person to investigate or t ...
, or
burns Matthew James Burns (born 31 October 1985), better known mononym A mononymous person is an individual who is known and addressed by a single name, or mononym. In some cases, that name has been selected by the individual, who may have originall ...
.


History

Swedish chemist
Carl Wilhelm Scheele Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a German and Swedish Pomerania Swedish Pomerania ( sv, Svenska Pommern; german: Schwedisch-Pommern) was a Dominion The word Dominion was used from 1907 to 1948 to refer to one of ...

Carl Wilhelm Scheele
was the first person to isolate lactic acid in 1780 from sour
milk Milk is a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, any ...

milk
. The name reflects the '' lact-'' combining form derived from the Latin word ''
lac Lac is the resinous secretion of a number of species of lac insects, of which the most commonly cultivated is ''Kerria lacca ''Kerria lacca'' is a species of insect in the family Kerriidae ''Kerriidae'' is a family of Coccoidea, scale insec ...

lac
'', which means milk. In 1808,
Jöns Jacob Berzelius Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only Jacob Berzelius, 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle Robert Boyle (; 25 January 1627 – ...

Jöns Jacob Berzelius
discovered that lactic acid (actually -lactate) also is produced in
muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly cat ...

muscle
s during exertion. Its structure was established by
Johannes Wislicenus Johannes Wislicenus (24 June 1835 – 5 December 1902) was a German chemist, most famous for his work in early stereochemistry. Biography The son of the radical Protestant theologian Gustav Wislicenus, Johannes was born on 24 June 1835 in Kl ...

Johannes Wislicenus
in 1873. In 1856, the role of ''
Lactobacillus ''Lactobacillus'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology Biology is the natural science that studies life and living organisms, including ...
'' in the synthesis of lactic acid was discovered by
Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, fermentation, microbial fermentation, and pasteurization. His research in chemi ...

Louis Pasteur
. This pathway was used commercially by the German
pharmacy Pharmacy is the clinical health science The following Outline (list), outline is provided as an overview of and topical guide to health sciences: Health sciences – are those sciences which focus on health, or health care, as core p ...

pharmacy
Boehringer Ingelheim C.H. Boehringer Sohn AG & Ko. is the parent company of the Boehringer Ingelheim group, which was founded in 1885 by Albert Boehringer in Ingelheim am Rhein, Germany. As of 2018, Boehringer Ingelheim is one of the world's List of largest pharmaceu ...

Boehringer Ingelheim
in 1895. In 2006, global production of lactic acid reached 275,000 tonnes with an average annual growth of 10%.


Production

Lactic acid is produced industrially by bacterial
fermentation Fermentation is a metabolism, metabolic process that produces chemical changes in organic Substrate (chemistry), substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in ...

fermentation
of
carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a ...
s, or by chemical synthesis from
acetaldehyde Ethanal (common name acetaldehyde) is an organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
.H. Benninga (1990): "A History of Lactic Acid Making: A Chapter in the History of Biotechnology". Volume 11 of ''Chemists and Chemistry''. Springer, , 9780792306252 In 2009, lactic acid was produced predominantly (70–90%) by fermentation. Production of racemic lactic acid consisting of a 1:1 mixture of and stereoisomers, or of mixtures with up to 99.9% -lactic acid, is possible by microbial fermentation. Industrial scale production of -lactic acid by fermentation is possible, but much more challenging.


Fermentative production

Fermented milk products Fermented milk products or fermented dairy products, also known as cultured dairy foods, cultured dairy products, or cultured milk products, are dairy foods Dairy products or milk products are a type of food produced from or containing the milk ...
are obtained industrially by fermentation of
milk Milk is a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, any ...

milk
or
whey Whey is the liquid remaining after milk Milk is a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a ...

whey
by ''Lactobacillus'' bacteria: ''
Lactobacillus acidophilus ''Lactobacillus acidophilus'' (New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. L ...
'', ''
Lactobacillus casei ''Lactobacillus casei'' is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group ...
'', ''Lactobacillus delbrueckii'' subsp. ''bulgaricus'' (''Lactobacillus bulgaricus''), ''
Lactobacillus helveticus ''Lactobacillus helveticus'' is a lactic-acid producing, rod-shaped bacterium of the genus ''Lactobacillus ''Lactobacillus'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classifica ...
'', ''
Lactococcus lactis ''Lactococcus lactis'' is a Gram-positive bacterium used extensively in the production of buttermilk and cheese, but has also become famous as the first genetically modified organism to be used alive for the treatment of human disease. ''L. lact ...

Lactococcus lactis
'', and ''Streptococcus salivarius'' subsp. ''thermophilus'' (''Streptococcus thermophilus''). As a starting material for industrial production of lactic acid, almost any carbohydrate source containing and C6 sugars can be used. Pure sucrose, glucose from starch, raw sugar, and beet juice are frequently used. 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 Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
/
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
.


Chemical production

Racemic lactic acid is synthesized industrially by reacting
acetaldehyde Ethanal (common name acetaldehyde) is an organic chemical compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds ...
with
hydrogen cyanide Hydrogen cyanide, sometimes called prussic acid, is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical ...

hydrogen cyanide
and hydrolysing the resultant . When
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord fo ...

hydrolysis
is performed by
hydrochloric acid Hydrochloric acid +(aq) Cl−(aq) or H3O+ Cl− also known as muriatic acid, is an aqueous solution An aqueous solution is a solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a salin ...

hydrochloric acid
,
ammonium chloride Ammonium chloride is an inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, ...

ammonium chloride
forms as a by-product; the Japanese company Musashino is one of the last big manufacturers of lactic acid by this route. Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials (
vinyl acetate Vinyl acetate is an organic compound with the Chemical formula, formula CH3CO2CH=CH2. This colorless liquid is the precursor to polyvinyl acetate and ethylene-vinyl acetate, ethene-vinyl acetate copolymers, important industrial polymers. Producti ...

vinyl acetate
,
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
, etc.) by application of catalytic procedures.


Biology


Molecular biology

-Lactic acid is the primary
endogenous Endogenous substances and processes are those that originate from within a system such as an organism, Tissue (biology), tissue, or Cell (biology), cell. Endogenous substances and processes contrast with exogenous ones, such as Drug, drugs, which ...
agonist An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. In contrast, an antagonist blocks the action of the agonist, while an inverse agonist causes an action opposite to that of the agonist ...

agonist
of hydroxycarboxylic acid receptor 1 (HCA1), a
G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of protein family, evolutionar ...
(GPCR).


Exercise and lactate

During power exercises such as
sprinting Sprinting is running over a short distance at the top-most speed of the body in a limited period of time. It is used in many sports that incorporate running, typically as a way of quickly reaching a target or goal, or avoiding or catching an op ...
, when the rate of demand for energy is high,
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
is broken down and oxidized to
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

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 Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GA3P, GADP, GAP, TP, GALP or PGAL, is the metabolite In biochemistry Biochemistry or biological chemistry, is the study of chemical ...

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. The resulting lactate can be used in two ways: *
Oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

Oxidation
back to
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate acid, conjugate base, CH3COCOO−, is a key intermediate in several metabolic pathways throughout the c ...

pyruvate
by well-oxygenated
muscle Skeletal muscles (commonly referred to as muscles) are organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly cat ...

muscle
cells, heart cells, and brain cells **Pyruvate is then directly used to fuel the
Krebs cycle The citric acid cycle (CAC) – also known as the TCA cycle (tricarboxylic acid cycle) or the Krebs cycle – is a series of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set o ...
*Conversion to
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
via
gluconeogenesis Gluconeogenesis (GNG) is a metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformati ...

gluconeogenesis
in the liver and release back into circulation; see
Cori cycle The Cori cycle (also known as the lactic acid cycle), named after its discoverers, Carl Ferdinand Cori Carl Ferdinand Cori, ForMemRS (December 5, 1896 – October 20, 1984) was a Czech-American biochemist Biochemists are scientists who are t ...
**If blood glucose concentrations are high, the glucose can be used to build up the liver's
glycogen Glycogen is a multibranched polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant found in . They are long chain carbohydrates composed of units bound together by . This carbohydrate can react with water () usi ...

glycogen
stores. However, lactate is continually formed at rest and during all exercise intensities. With the use of stable isotopic tracers George Brooks and colleagues, at the University of California, Berkeley, observed that lactate served as a metabolic fuel being produced and oxidatively disposed in resting and exercising muscle. Some causes of this are metabolism in
red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek language, Greek ''erythros'' for "red" and ''k ...

red blood cell
s that lack mitochondria, and limitations resulting from the enzyme activity that occurs in muscle fibers having high glycolytic capacity. In 2004, Robergs ''et al.'' maintained that lactic acidosis during exercise is a "construct" or myth, pointing out that part of the H+ comes from ATP hydrolysis (ATP4− + H2O → ADP3− + + H+), and that reducing pyruvate to lactate (pyruvate + NADH + H+ → lactate + NAD+) actually consumes H+. Lindinger ''et al''. countered that they had ignored the causative factors of the increase in + After all, the production of lactate from a neutral molecule must increase +to maintain electroneutrality. The point of Robergs's paper, however, was that lactate is produced from pyruvate, which has the same charge. It is pyruvate production from neutral glucose that generates H+: Although the reaction glucose → 2 lactate + 2 H+ releases two H+ when viewed on its own, the H+ are absorbed in the production of ATP. On the other hand, the absorbed acidity is released during subsequent hydrolysis of ATP: ATP4− + H2O → ADP3− + + H+. So once the use of ATP is included, the overall reaction is :C6H12O6 → 2  + 2 H+ The generation of CO2 during respiration also causes an increase in +


Neural tissue energy source

Although
glucose Glucose is a simple with the . Glucose is the most abundant , a subcategory of s. Glucose is mainly made by and most during from water and carbon dioxide, using energy from sunlight, where it is used to make in s, the most abundant carbohydr ...

glucose
is usually assumed to be the main energy source for living tissues, there are a few reports that indicate that it is lactate, and not glucose, that is preferentially metabolized by
neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous system In biology Biology is the natural science that studies life and living ...

neuron
s in the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tis ...

brain
of several
mammalian Mammals (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of t ...
species (the notable ones being
mice A mouse, plural mice, is a small mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ...

mice
,
rat Rats are various medium-sized, long-tailed rodent Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area a ...

rat
s, and
human Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A speci ...

human
s). According to the lactate-shuttle hypothesis,
glia Glia, also called glial cells (singular ''gliocyte'') or neuroglia, are non-neuron A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapse In the nervous s ...

glia
l cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons. Because of this local metabolic activity of glial cells, the
extracellular fluid In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, ...
immediately surrounding neurons strongly differs in composition from the
blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
or
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochor ...
, being much richer with lactate, as was found in
microdialysis Microdialysis is a minimally-invasive sampling technique that is used for continuous measurement of free, unbound analyte concentrations in the extracellular This glossary of biology terms is a list of definitions of fundamental terms and conc ...
studies.


Brain development metabolism

Some evidence suggests that lactate is important at early stages of development for brain metabolism in
prenatal Prenatal development () includes the development of the embryo and of the foetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo An embryo is the early stage of ...
and early
postnatal The postpartum (or postnatal) period begins immediately after childbirth Childbirth, also known as labour or delivery, is the ending of pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring In ...
subjects, with lactate at these stages having higher concentrations in body liquids, and being utilized by the brain preferentially over glucose. It was also hypothesized that lactate may exert a strong action over
GABA ''gamma-''Aminobutyric acid, or γ-aminobutyric acid , or GABA , is the chief inhibitory An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential that makes a postsynaptic neuron less likely to generate an action potent ...

GABA
ergic networks in the developing brain, making them more
inhibitory An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential Synaptic potential refers to the potential difference across the postsynaptic membrane that results from the action of neurotransmitters at a neuronal synapse. In other w ...
than it was previously assumed, acting either through better support of metabolites, or alterations in base intracellular levels, or both. Studies of brain slices of mice show that , 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''. 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 predominately from activity-induced concentration changes to the cellular NADH pools." 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.


Blood testing

Blood test A blood test is a laboratory A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which or technological research, s, and may be performed. Laboratory services are provided in a variety of settings: ...

Blood test
s for lactate are performed to determine the status of the acid base homeostasis in the body. Blood sampling for this purpose is often
arterial An artery (plural arteries) () is a blood vessel that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pulmonary arteries, pulmonary ...
(even if it is more difficult than
venipuncture In medicine, venipuncture or venepuncture is the process of obtaining intravenous access for the purpose of venous blood sampling (also called ''phlebotomy Phlebotomy is the process of making a puncture in a vein Veins are blood vessels tha ...
), because lactate levels differ substantially between arterial and venous, and the arterial level is more representative for this purpose. During
childbirth Childbirth, also known as labour or delivery, is the ending of pregnancy Pregnancy, also known as gestation, is the time during which one or more offspring In biology, offspring are the young born of living organism, organisms, produc ...

childbirth
, lactate levels in the fetus can be quantified by
fetal scalp blood testing Fetal scalp blood testing is a technique used in obstetrics during childbirth, labor to confirm whether fetal oxygenation is sufficient. The procedure can be performed by creating a shallow cut by a transvaginal (disambiguation), transvaginally ins ...
.


Polymer precursor

Two molecules of lactic acid can be dehydrated to the
lactoneLactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

lactone
lactide Lactide is the lactone cyclic di-ester derived from lactic acid (2-hydroxypropionic acid). With the formula (OCHCO2)2, it exists in three different stereoisomeric forms. All are colorless or white solids. Lactide has attracted great interest beca ...

lactide
. In the presence of
catalysts that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules ...
lactide polymerize to either atactic or
syndiotactic Tacticity (from Greek τακτικός ''taktikos'' "of or relating to arrangement or order") is the relative stereochemistry Stereochemistry, a subdiscipline of chemistry Chemistry is the study of the properties and behavior of . It is ...

syndiotactic
polylactide Polylactic acid, or polylactide (PLA) is a thermoplastic A thermoplastic, or thermosoftening plastic, is a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplasti ...
(PLA), which are
biodegradable Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. Mechanisms The process of biodegradation can be divided into three stages: biodeterioration, biofragmentation, and assimilation (biology), assimila ...

biodegradable
polyester Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include natural ...
s. PLA is an example of a plastic that is not derived from
petrochemical Petrochemicals (sometimes abbreviated as petchems) are the chemical products Products are the species formed from chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance ...
s.


Pharmaceutical and cosmetic applications

Lactic acid is also employed in
pharmaceutical technology Pharmaceutics is the discipline of pharmacy that deals with the process of turning a new chemical entity (NCE) or old drugs into a medication to be used safely and effectively by patients. It is also called the science of dosage form design. There ...
to produce water-soluble lactates from otherwise-insoluble active ingredients. It finds further use in topical preparations and
cosmetics Cosmetics are constituted mixtures of chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and take ...
to adjust acidity and for its
disinfectant A disinfectant is a chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
and
keratolytic Keratolytic () therapy is a type of medical treatment to remove warts, calluses and other lesions in which the epidermis The epidermis is the outermost of the three layers that make up the skin, the inner layers being the dermis and Subcutaneo ...
properties.


Foods

Lactic acid is found primarily in sour
milk Milk is a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, any ...

milk
products, such as
kumis ''Kumis'' (also spelled ''kumiss'' or ''koumiss'' or ''kumys'', see other transliteration Transliteration is a type of conversion of a text from one script Script may refer to: Writing systems * Script, a distinctive writing system, b ...

kumis
,
labanLaban is a French language, French surname. It may refer to: Places * Laban-e Olya, a village in Iran * Laban-e Sofla, a village in Iran * Laban, Virginia, an unincorporated community in the United States * 8539 Laban, main-belt asteroid People S ...
,
yogurt Yogurt (; , from tr, yoğurt) also spelled yoghurt, yogourt or yoghourt, is a food produced by bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell ...

yogurt
,
kefir Kefir (also spelled as kephir or kefier, ; ; ) ( ), is a fermented milk drink similar to a thin yogurt Yogurt (; , from tr, yoğurt) also spelled yoghurt, yogourt or yoghourt, is a food produced by bacteria Bacteria (; common ...

kefir
, and some
cottage cheese Cottage cheese is a simple fresh cheese curd product with a mild flavor and a creamy, non-homogenous, soupy texture. It is also known as curds and whey. It is made from Cow’s milk, cow's milk by draining the cheese, as opposed to pressing it to ...
s. The
casein Casein ( , from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in rel ...

casein
in fermented milk is coagulated (curdled) by lactic acid. Lactic acid is also responsible for the sour flavor of
sourdough Sourdough is a bread Bread is a staple food prepared from a dough of flour and water, usually by baking. Throughout recorded history, it has been a prominent food in large parts of the world. It is one of the oldest man-made foods, having ...

sourdough
bread. 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. If this is the case then the calculated
food energy Food energy is chemical energy Chemical energy is the energy of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havin ...
may use the standard per gram that is often used for all carbohydrates. But in some cases lactic acid is ignored in the calculation. The energy density of lactic acid is per 100 g. Some beers (
sour beer Sour beer is beer Beer is one of the oldest and most widely consumed alcoholic drink An alcoholic drink is a drink A drink (or beverage) is a liquid A liquid is a nearly incompressible fluid In physics, a fluid is a subs ...
) purposely contain lactic acid, one such type being Belgian
lambic Lambic () is a type of beer Beer is one of the oldest and most widely consumed alcoholic drinks in the world, and the third most popular drink overall after water and tea. Beer is brewing, brewed from cereal, cereal grains—most commonly ...
s. 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 Wort () is the liquid extracted from the mashing In brewing and distilling, mashing is the process of combining a mix of grains – typically malted barley with supplementary grains such as corn Maize ( ; ''Zea mays'' subsp. ''mays'' ...

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 Berliner Weisse (German: Berliner Weiße, ) is a cloudy, sour beer Sour beer is beer Beer is one of the oldest and most widely consumed alcoholic drink An alcoholic drink is a drink that contains ethanol Ethanol (also called ethyl ...

Berliner weisse
, Flanders red and
American wild aleAmerican wild ale generally refers to beers brewed in America using yeast or bacteria in addition to ''Saccharomyces cerevisiae'' for Brewing#Fermenting, fermentation. Such beers may be similar to traditional beers such as Lambic and Oud bruin, and a ...
. In winemaking, a bacterial process, natural or controlled, is often used to convert the naturally present
malic acid Malic acid is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavi ...
to lactic acid, to reduce the sharpness and for other flavor-related reasons. This
malolactic fermentation Malolactic conversion (also known as malolactic fermentation or MLF) is a process in winemaking in which Tart (flavor), tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation is ...

malolactic fermentation
is undertaken by
lactic acid bacteria Lactobacillales are an order of gram-positive, GC-content, low-GC, acid-tolerant, generally nonsporulating, Aerotolerant anaerobe, nonrespiring, either rod-shaped (bacillus (shape), bacilli) or spherical (cocci) bacteria that share common metab ...
. While not normally found in significant quantities in fruit, lactic acid is the primary organic acid in
akebia ''Akebia'' is a genus of five species of flowering plant, within the family Lardizabalaceae. The scientific name, ''akebia'', is a Latinization of the Japanese language, Japanese name for species Akebia quinata: . Species There are five species: ...

akebia
fruit, making up 2.12% of the juice. As a
food additive Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology ...
it is approved for use in the EU, USA and Australia and New Zealand; it is listed by its
INS numberThe International Numbering System for Food Additives (INS) is a Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to s ...
270 or as
E number E numbers ("E" stands for "Europe") are codes for substances used as food additive Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμ ...
E270. Lactic acid is used as a food preservative, curing agent, and flavoring agent. It is an ingredient in processed foods and is used as a decontaminant during meat processing. Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis. Carbohydrate sources include corn, beets, and cane sugar.


Forgery

Lactic acid has historically been used to assist with the erasure of inks from official papers to be modified during
forgery Forgery is a white-collar crime The term "white-collar crime" refers to financially motivated, nonviolent or non directly violent crime In ordinary language, a crime is an unlawful act punishable by a state or other authority. Th ...
.


Cleaning products

Lactic acid is used in some liquid cleaners as a
descaling agent A descaling agent or chemical descaler is a liquid chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All every ...
for removing
hard water Hard water is water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and th ...
deposits such as
calcium carbonate Calcium carbonate is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togethe ...

calcium carbonate
, forming the lactate,
calcium lactate Calcium lactate is a white crystalline salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystallin ...

calcium lactate
. Owing to its high acidity, such deposits are eliminated very quickly, especially where boiling water is used, as in kettles. It also is gaining popularity in antibacterial dish detergents and hand soaps replacing
Triclosan Triclosan (sometimes abbreviated as TCS) is an antibacterial An antibiotic is a type of antimicrobial An antimicrobial is an agent that kills microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In b ...

Triclosan
.


See also

* Hydroxybutyric acid *
Acids in wine The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality o ...
* Alanine cycle *
Biodegradable plastic Biodegradable plastics are plastic Plastics are a wide range of syntheticA synthetic is an artificial material produced by organic chemistry, organic chemical synthesis. Synthetic may also refer to: In the sense of both "combination" and ...
*
Dental caries Tooth decay, also known as dental caries or cavities, is the breakdown of teeth A tooth (plural teeth) is a hard, calcification, calcified structure found in the jaws (or mouths) of many vertebrates and used to Mastication, break down food. ...

Dental caries
*, a lactate transporter *
Thiolactic acid Thiolactic acid is the organosulfur compound with the formula HSCH2CO2H. The molecule contains both carboxylic acid and thiol functional groups. It is structurally related to lactic acid by the interchange of SH for OH. It is a colorless oil. Th ...

Thiolactic acid


References


External links


Corn Plastic to the Rescue

Lactic Acid: Information and Resources


* {{Authority control Food acidity regulators Alpha hydroxy acids Exercise physiology Preservatives Propionic acids E-number additives