Lactic acid

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Lactic acid

Lactic acid (IUPAC systematic name

Systematic name

There are millions of possible objects that can be described in science, too many to create common names for every one. As a response, a number of systems of systematic names have been created....
: 2-hydroxypropanoic acid), also known as milk acid, is a chemical compound

Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
that plays a role in several biochemical

Biochemistry

Biochemistry is the study of the chemistry processes in living organisms. It deals with the structure and function of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules....
processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele

Carl Wilhelm Scheele

Carl Wilhelm Scheele was a Germany-Sweden pharmaceutical chemist, born in Stralsund, Western Pomerania, Germany . He was the discoverer of many chemical substances, most notably discovering oxygen , molybdenum and chlorine before Humphry Davy....
, and is a carboxylic acid

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
with a chemical formula

Chemical formula

A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound, and how the relationship between those atoms changes in chemical reactions....
of C₃H₆O₃. It has a hydroxyl

Hydroxyl

Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl Radical and the hydroxyl anion is called a hydroxide....
group adjacent to the carboxyl group, making it an alpha hydroxy acid

Alpha hydroxy acid

a-hydroxy acids, or alpha hydroxy acids , are a class of chemical compounds that consist of a carboxylic acid substituted with a hydroxyl on the adjacent carbon....
(AHA). In solution, it can lose a proton

Proton

Ion

An ion is an atom or molecule which has lost or gained one or more electrons, giving it a positive or negative electrical charge. According to the Bohr_model this will be from or in the outer shield 'n'....
CH₃CH(OH)COO^-.

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Encyclopedia

Lactic acid (IUPAC systematic name

Systematic name

Chemical compound

Biochemistry

Carl Wilhelm Scheele

Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
with a chemical formula

Chemical formula

Hydroxyl

Alpha hydroxy acid

Proton

Ion

Hygroscopy

Hygroscopy is the ability of a substance to attract water molecules from the surrounding Natural environment through either absorption or adsorption....
.

Lactic acid is chiral

Chirality (chemistry)

The term chiral is used to describe an object that is non-Superposition on its mirror image.Human hands are perhaps the most universally recognized example of chirality: The left hand is a non-superposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands...
and has two optical isomers. One is known as L-(+)-lactic acid or (S)-lactic acid and the other, its mirror image, is D-(-)-lactic acid or (R)-lactic acid. L-(+)-Lactic acid is the biologically important isomer.

In animals, L-lactate is constantly produced from pyruvate via the enzyme

Enzyme

Enzymes are biomolecules that catalysis chemical reactions. Almost all enzymes are proteins. In enzymatic reactions, the molecules at the beginning of the process are called Substrate , and the enzyme converts them into different molecules, the products....
lactate dehydrogenase

Lactate dehydrogenase

Lactate dehydrogenase is an enzyme present in a wide variety of organisms, including plants and animals....
(LDH) in a process of fermentation

Fermentation (biochemistry)

Fermentation is the process of deriving energy from the Redox of organic compounds, such as carbohydrates, using an Endogeny electron acceptor, which is usually an organic compound....
during normal metabolism

Metabolism

Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments....
and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal which is governed by a number of factors including: monocarboxylate transporters, concentration and isoform of LDH and oxidative capacity of tissues. The concentration of blood

Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports waste products away from those same cells....
lactate is usually 1–2 mmol/L at rest, but can rise to over 20 mmol/L during intense exertion.

Industrially, lactic acid fermentation

Lactic acid fermentation

Lactic acid fermentation is a biological process by which sugars such as glucose, fructose, and sucrose, are converted into cellular energy and the metabolic product fermental acid....
is performed by Lactobacillus
Lactobacillus

Lactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic bacteria. They are a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid....
bacteria

Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
, among others. These bacteria can operate in the mouth

Mouth

The mouth, buccal cavity, or oral cavity is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking up the solid food particles into smaller pieces and mixing them with saliva....
; the acid

Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
they produce is responsible for the tooth

Tooth

Teeth are small whitish structures found in the jaws of many vertebrates that are used to tear, scrape, and chew food. Some animals, particularly carnivores, also use teeth for hunting or defense....
decay known as caries

Caries

Caries is a progressive destruction of any kind of bone structure, including the skull, ribs and other bones, or the tooth. Caries can be caused by osteomyelitis, which is a bacterial disease....
.

In medicine

Medicine

Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, lactate is one of the main components of Ringer's lactate or lactated Ringer's solution

Lactated Ringer's solution

Lactated Ringer's solution is a solution that is Tonicity with blood and intended for intravenous therapy. Veterinary administration may also be subcutaneous....
(Compound Sodium Lactate

Hartmann's Solution

Hartmann's solution or Compound Sodium Lactate is a solution that is Tonicity with blood and intended for intravenous therapy.Hartmann's solution is abbreviated as "CSL"....
or Hartmann's Solution

Hartmann's Solution

Sodium

Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
and potassium

Potassium

Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
cations, with lactate and chloride

Chloride

The chloride ion is formed when the chemical element chlorine picks up one electron to form an anion Cl−....
anions, in solution with distilled water

Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
in concentration so as to be isotonic

Isotonic

The term isotonic may refer to;* Isometric exercise and Weight training#Isotonic, Isometric and Plyometric exercises* Isotonic for the term associated with muscle contraction...
compared to human

Human

A human being, also human or man, is a member of a species of bipedalism primates in the family Hominidae . Mitochondrial DNA evidence indicates that modern humans originated in east Africa about 200,000 years ago....
blood

Blood

Blood is a specialized bodily fluid that delivers necessary substances to the body's Cell s ? such as nutrients and oxygen ? and transports waste products away from those same cells....
. It is most commonly used for fluid resuscitation after blood loss due to trauma

Physical trauma

Physical trauma refers to a body injury. A trauma patient is someone who has suffered serious and life-threatening physical injury with the potential for secondary complications such as Shock , respiratory failure and death....
, surgery

Surgery

Surgery is a medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, to help improve bodily function or appearance, or sometimes for some other reason....
, or a burn injury

Burn (injury)

A burn is a type of injury that may be caused by heat, Temperature, electricity, chemicals, light, radiation, or friction. Burns can be highly variable in terms of the tissue affected, the severity, and resultant complications....
.

Exercise and lactate

During power exercises such as sprinting

Sprint (race)

Sprints are short running races in athletics . They are roughly classified as events in which top runners will not have to "pace themselves", but can run as fast as possible for the entire distance....
, when the rate of demand for energy is high, lactate is produced faster than the ability of the tissues to remove it and lactate concentration begins to rise. This is a beneficial process since the regeneration of NAD⁺

Nicotinamide adenine dinucleotide

Nicotinamide adenine dinucleotide, abbreviated NAD+, is a coenzyme found in all living cell s. The compound is a dinucleotide, since it consists of two nucleotides joined through their phosphate groups: with one nucleotide containing an adenine base, and the other containing nicotinamide....
ensures that energy production is maintained and exercise can continue. The increased lactate produced can be removed in a number of ways including

oxidation to pyruvate by well-oxygenated muscle
MUSCLE

MUSCLE is public domain, multiple sequence alignment software for protein and nucleotide sequences.MUSCLE is integrated into UGENE bioinformatics tool as a plugin....
cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
which is then directly used to fuel the citric acid cycle
Citric acid cycle

The citric acid cycle ? also known as the tricarboxylic acid cycle ; the Krebs cycle; or, more rarely, the Szent-Gy?rgyi-Krebs cycle) ? is a series of enzyme-catalysed chemical reactions of central importance in all living cell s that use oxygen as part of cellular respiration....
,
conversion to glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
via the Cori cycle
Cori cycle

The Cori cycle, named after its discoverers, Carl Cori and Gerty Cori, refers to the metabolic pathway in which lactic acid produced by anaerobic glycolysis in the muscles moves to the liver and is converted to glucose, which then returns to the muscles and is converted back to lactate....
in the liver through the process of gluconeogenesis
Gluconeogenesis

Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactic acid, glycerol, and glucogenic amino acids....
.

Contrary to popular belief, this increased concentration of lactate does not directly cause acidosis

Acidosis

Acidosis is an increased acidity . If not further qualified, it usually refers to acidity of the blood plasma.Acidosis is said to occur when arterial pH falls below 7.35, while its counterpart occurs at a pH over 7.45....
, nor is it responsible for delayed onset muscle soreness

Delayed onset muscle soreness

Delayed onset muscle soreness , also sometimes called muscle fever, is the pain or discomfort often felt 24 to 72 hours after exercising and subsides generally within 2 to 3 days....
. This is because lactate itself is not capable of releasing a proton

Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
, and secondly, the acidic form of lactate, lactic acid, cannot be formed under normal circumstances in human tissues. Analysis of the glycolytic pathway in humans indicates that there are not enough hydrogen ions present in the glycolytic intermediates to produce lactic or any other acid.

The acidosis

Acidosis

Acidosis is an increased acidity . If not further qualified, it usually refers to acidity of the blood plasma.Acidosis is said to occur when arterial pH falls below 7.35, while its counterpart occurs at a pH over 7.45....
that is associated with increases in lactate concentration during heavy exercise arises from a separate reaction. When ATP

Adenosine triphosphate

This article is about the chemical used by cells as an energy carrier. For other uses, see ATP .Adenosine-5'-triphosphate is a multifunctional nucleotide, and plays an important role in cell biology as a coenzyme that is the "molecule unit of currency" of intracellular energy transfer....
is hydrolysed

Hydrolysis

Hydrolysis is a chemical reaction during which one or more water are split into hydrogen and hydroxide ions which may go on to participate in further reactions....
, a hydrogen ion is released. ATP-derived hydrogen ions are primarily responsible for the decrease in pH. During intense exercise, aerobic metabolism cannot produce ATP quickly enough to supply the demands of the muscle. As a result, anaerobic metabolism

Lactic acid fermentation

Lactic acid fermentation is a biological process by which sugars such as glucose, fructose, and sucrose, are converted into cellular energy and the metabolic product fermental acid....
becomes the dominant energy producing pathway as it can form ATP at high rates. Due to the large amounts of ATP being produced and hydrolysed in a short period of time, the buffering

Buffer solution

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It has the property that the pH of the solution changes very little when a small amount of acid or base is added to it....
systems of the tissues are overcome, causing pH to fall and creating a state of acidosis, a natural process which facilitates the easier dissociation of Oxyhaemoglobin and allows easier transfer of oxygen from the blood. This may be one factor, among many, that contributes to the acute muscular discomfort experienced shortly after intense exercise.

The effect of lactate on acidosis has been the topic of many recent conferences in the field of exercise physiology. Robergs et al. have accurately chased the proton movement that occurs during glycolysis. However, in doing so, they have suggested that [H⁺] is an independent variable that determines its own concentration. A recent review by Lindinger et al. has been written to rebut the stoichiometric approach used by Robergs et al (2004). In using this stoichiometric process, Robergs et al. have ignored the causative factors (independent variables) of the concentration of hydrogen ions (denoted [H⁺]). These factors are strong ion difference [SID], PCO₂, and weak acid buffers. Lactate is a strong anion, and causes a reduction in [SID] which causes an increase in [H⁺] to maintain electroneutrality. PCO₂ also causes an increase in [H⁺]. During exercise, the intramuscular lactate concentration and PCO₂ increase, causing an increase in [H⁺], and thus a decrease in pH. (See Le Chatelier's principle

Le Châtelier's principle

In chemistry, Le Chatelier's Principle, also called the Le Chatelier-Braun principle, can be used to predict the effect of a change in conditions on a chemical equilibrium....
)

Lactic acid as a polymer precursor

Two molecules of lactic acid can be dehydrated to lactide

Lactide

Lactide is the cyclic di-ester of lactic acid, i.e., 2-hydroxypropionic acid. Lactic acid can not form a lactone as other hydroxy acids do because the hydroxy group is too close to the carboxylic group....
, a cyclic lactone. A variety of catalysts can polymerise lactide to either heterotactic or syndiotactic polylactide

Polylactic acid

Polylactic acid or polylactide is a biodegradable, thermoplastic, aliphatic polyester derived from renewable resources, such as corn starch or sugarcanes ....
, which as biodegradable polyester

Polyester

Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate ....
s with valuable (inter alia) medical properties are currently attracting much attention.

Nowadays, lactic acid is used as a monomer for producing polylactic acid

Polylactic acid

Polylactic acid or polylactide is a biodegradable, thermoplastic, aliphatic polyester derived from renewable resources, such as corn starch or sugarcanes ....
(PLA) which later has application as biodegradable plastic. This kind of plastic is a good option for substituting conventional plastic produced from petroleum oil because of low emission of carbon dioxide that can contribute to global warming. The commonly used process in producing lactic acid is via fermentation, and later to obtain the polylactic acid, the polymerization process follows.

Lactic acid in foods

Lactic acid is primarily found in sour milk

Milk

Milk is an opaque white liquid produced by the mammary glands of female mammals . It provides the primary source of nutrition for newborn mammals before they are able to digestion other types of food....
products, such as: koumiss, leban, yogurt, kefir

Kefir

Kefir is a Fermentation milk drink that originated in the Caucasus region. It is prepared by inoculating Cattle, goat, or sheep's milk with kefir grains....
, and some cottage cheese

Cottage cheese

Cottage cheese is a cheese curd product with a mild flavor. It is drained, but not pressed so some whey remains. The curd is usually washed to remove acidity giving sweet curd cheese....
s. The casein

Casein

Casein is the predominant phosphoprotein that accounts for nearly 80% of proteins in cow milk and cheese. Milk-clotting proteases act on the soluble portion of the caseins, K-Casein, thus originating an unstable micelle state that results in clot formation....
in fermented milk is coagulated (curdled) by lactic acid.

Although it can be fermented

Fermentation (food)

Fermentation in food processing typically refers to the conversion of sugar to alcohol using yeast under anaerobic conditions. A more general definition of fermentation is the chemical conversion of carbohydrates into alcohols or acids....
from lactose

Lactose

Lactose is a sugar that is found most notably in milk. Lactose makes up around 2?8% of milk . The name comes from the Latin word for milk, plus the -ose ending used to name sugars....
(milk sugar), most commercially used lactic acid is derived by using bacteria such as Streptococcus thermophilus
Streptococcus thermophilus

Streptococcus salivarius subsp. thermophilus is a Gram-positive Facultative anaerobic organism. It is a cytochrome-, oxidase- and catalase-negative organism that is nonmotile, non-spore forming and homofermentative....
, Lactobacillus acidophilus
Lactobacillus acidophilus

Lactobacillus acidophilus is one species in the genus Lactobacillus. It is sometimes used commercially together with Streptococcus salivarius and Lactobacillus bulgaricus in the production of acidophilus-type yogurt....
, or Lactobacillus delbrueckii subsp. bulgaricus (formerly known as Lactobacillus bulgaricus
Lactobacillus bulgaricus

Lactobacillus delbrueckii subspecies bulgaricus is one of several bacterium used for the production of yogurt. It can also be found in other naturally fermented products....
) to ferment carbohydrates from nondairy sources such as cornstarch

Cornstarch

Cornstarch, or cornflour, is the starch of the corn grain. It is also grown from the endosperm, or white heart, of the corn seed. It has a distinctive appearance and feel when mixed raw with water or milk, giving easily to gentle pressure but resisting sudden pressure ....
, potato

Potato

The potato is a starchy, tuberous crop from the perennial plant Solanum tuberosum of the Solanaceae family. The word potato may refer to the plant itself as well....
es, and molasses

Molasses

Molasses is a thick by-product from the processing of the sugar beet or sugar cane into sugar. The word molasses comes from the Portuguese language word mela?o, which comes from "meli", the Greek word for "honey"....
. Thus, although it is commonly known as "milk acid", vegan products can contain lactic acid as an ingredient.

Lactic acid may also be found in various processed foods, usually either as a pH-adjusting ingredient, or as a preservative

Preservative

A preservative is a natural or synthetic chemical compound that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc....
(either as antioxidant

Antioxidant

An antioxidant is a molecule capable of slowing or preventing the Redox of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent....
or for control of pathogenic micro-organisms). It may also be used as a fermentation booster in rye and sourdough bread

Bread

Bread is a staple food prepared by baking a dough of flour and water. It may be leavened or unleavened. Edible salt, fat and a leavening agent such as yeast are common ingredients, though bread may contain a range of other ingredients: milk, Egg , sugar, spice, fruit , vegetables , Nut or seeds ....
s.

Potassium lactate

Potassium lactate

Potassium lactate is a Compound with formula KC3H5O3. It is the potassium salt of lactic acid. It is produced by neutralizing lactic acid which is fermented from a sugar source....
, sodium lactate

Sodium lactate

Sodium lactate is a Compound with formula NaC3H5O3. It is the sodium salt of lactic acid and has a mild saline taste....
, and calcium lactate

Calcium lactate

Calcium lactate is a white crystalline salt made by the action of lactic acid on calcium carbonate. It is used in foods and given medicinally. Its E number is E327....
are the neutralized salts of lactic acid. Potassium lactate is used in many fresh and cooked meat products for shelf life control, color preservation, and reduction of sodium content. Sodium lactate has a mild saline taste and is therefore suitable for flavor enhancement in meat products as well. Sodium lactate is being produced in solution as well as dry. Calcium lactate is popular for fortification and improved texture in emulsified meat products like frankfurters. Ready-to-eat meat and poultry products commonly contain sodium or potassium lactate to control Listeria monocytogenes
Listeria monocytogenes

Listeria monocytogenes, one of the most virulent foodborne pathogens with 20 percent of clinical infections resulting in death, is the causative agent of Listeriosis....
.

Lactic acid is also present in wheat beer

Wheat beer

Wheat beer is a beer that is brewing with a significant proportion of wheat. Wheat beers often also contain a significant proportion of malted barley....
s, especially lambic

Lambic

Lambic is a very distinctive type of beer brewed only in the Pajottenland region of Belgium . Lambic is the single key ingredient in the production of gueuze....
, due to the activity of Pediococcus damnosus.

Lactic acid is widely used for reducing the number of pathogenic bacteria like E.coli, Salmonella
Salmonella

Salmonella is a genus of rod-shaped Gram-negative enterobacteriaceae that causes typhoid fever, paratyphoid fever, and the foodborne illness salmonellosis....
, Campylobacter
Campylobacter

The genus Campylobacter, first discovered in 1963, describes Gram-negative, spiral, microaerophilic bacterium. Motile, with either uni- or bi-polar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive....
, and Listeria
Listeria

Listeria is a bacterial genus containing six species. Named after the English surgeon, Joseph Lister, Listeria species are Gram-positive bacilli and are typified by Listeria monocytogenes, the causative agent of listeriosis....
on animal carcasses like beef, pork, and poultry during the slaughtering process.

Lactic acid

Exercise and lactate

Lactic acid as a polymer precursor

Lactic acid in foods

See also

External links