LACTIC ACID


2-Hydroxypropanoic acid

Lactic acid
Milk acid

EC / List no.: 200-018-0
CAS no.: 50-21-5
Mol. formula: C3H6O3

Lactic acid was discovered in 1780 by Swedish chemist, Carl Wilhelm Scheele, who isolated the lactic acid from sour milk as an impure brown syrup and gave it a name based on its origins: 'Mjölksyra'. 
The French scientist Frémy produced lactic acid by fermentation and this gave rise to industrial production in 1881.
Lactic acid is produced by the fermentation of sugar and water or by chemical process and is commercially usually sold as a liquid.

Pure and anhydrous racemic lactic acid is a white crystalline solid with a low melting point. Lactic acid has two optical forms, L(+) and D(-) . 
L(+)-lactic acid is the biological isomer as it is naturally present in the human body.

How is lactic acid produced?
Lactic acid can be produced naturally or synthetically. Commercial lactic acid is produced naturally by fermentation of carbohydrates such as glucose, sucrose, or lactose. 
The current world market leader in the commercial production of lactic acid is Corbion Purac: www.corbion.com.

The natural production process is shown in the figure below. 
Wih the addition of lime or chalk, the raw materials are fermented in a fermenter and crude calcium lactate is formed. 
The gypsum is separated from the crude calcium lactate, which results in crude lactic acid. 
The crude lactic acid is purified and concentrated and L(+) lactic acid is the result.

LACTIC ACID, is an organic acid with applications in beer production as well as the cosmetic, pharmaceutical, food and chemical industries. 
Commonly used as a preservative and antioxidant. 
It also has uses as a fuel additive, chemical intermediate, acidity regulator, and disinfectant.

One specific use of LACTIC ACID is in I.V solutions, where it is an electrolyte to help replenish the bodies fluids. 
It is also used in dialysis solutions, which results in a lower incidence of side effects compared to Sodium Acetate which can also be used.

LACTIC ACID comes in both R (D-) and S (L+) enantiomers which can be manufactured individually to near perfect optical purity. 
This means LACTIC ACID is great in the production of other products which require a specific stereochemistry.

LACTIC ACID is used frequently in the cosmetic industry due to the effect of promoting collagen production, helping to firm the skin against wrinkles and sagging. 
It can also cause micro peeling, which can help reduce various scars and age spots. 
This is a great solution for people with sensitive or dry skin where exfoliants don’t work.


SYNONYMS: 2-Hydroxypropanoic acid; Lactic acid;1-Hydroxyethanecarboxylic acid; Ethylidenelactic acid; alpha-Hydroxypropionic Acid; Milchsäure (Dutch); ácido lactico (Spanish); Aacide lactique (French);

Synonyms
(RS)-2-Hydroxypropionsaeure; 1-Hydroxyethanecarboxylic acid; 2-Hydroxypropanoic acid; 2-Hydroxypropionic acid; Acidum lacticum; Aethylidenmilchsaeure; DL-Lactic acid; DL-Milchsaeure; Ethylidenelactic acid; Kyselina 2-hydroxypropanova [Czech]; Kyselina mlecna [Czech]; Lactate; Lactic acid, dl-; Lactic acid (natural); Lactic acid USP; Lactovagan; Milchsaeure; Milchsaure [German]; Milk acid; Ordinary lactic acid; Propanoic acid, 2-hydroxy-; Propel; Propionic acid, 2-hydroxy-; Racemic lactic acid; SY-83; Tonsillosan; alpha-Hydroxypropionic acid; [ChemIDplus]

Sources/Uses
Used as a solvent and acidulant in the production of foods, drugs, and dyes; Also used as a mordant in woolen goods printing, a soldering flux, a dehairing agent, and a catalyst for phenolic resins; Also used in leather tanning, oil well acidizing, and as a plant growth regulator

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.

Lactic acid, also named ‘milk acid’, is an organic acid with the following chemicalformula: CH3CH(OH)CO2H. 
The official name given by the International Union ofPure and Applied Chemistry (IUPAC) is 2-hydroxypropanoic acid. 
This important acid can be naturally produced (Martinez et al. 2013), but its importanceis correlated with synthetic productions. 
Pure lactic acid is a colourless andhydroscopic liquid; it can be defined a weak acid because of its partial dissociationin water and the correlated acid dissociation constant (Ka= 1.38 10−4).

Lactic acid is a chiral compound with a carbon chain composed of a central (chiral) atomand two terminal carbon atoms. 
A hydroxyl group is attached to the chiral carbon atom while oneof the terminal carbon atoms is part of the carboxylic group and the other atom is part of the methylgroup. 
Consequently, two optically active isomeric forms of lactic acid exist: L(+) form, alsonamed (S)-lactic acid, and D(−) form, or (R)-lactic acid. L(+)-lactic acid is the biological isomer.

Antibacterial mechanism of lactic acid on physiological and morphological properties of Salmonella Enteritidis, Escherichia coli and Listeria monocytogenes:
•Pathogens could be completely inactivated after exposure to lactic acid.
•Lactic acid resulted in great leakage of protein of three pathogens.
•Bacterial protein bands of lactic acid-treated cells got fainter or disappeared.
•Z-Average sizes of pathogens were changed to smaller after lactic acid treatment.
•Lactic acid caused collapsed or even broken cells with obvious pits and gaps.

Lactic acid is widely used to inhibit the growth of important microbial pathogens, but its antibacterial mechanism is not yet fully understood. 
The objective of this study was to investigate the antibacterial mechanism of lactic acid on Salmonella Enteritidis, Escherichia coli and Listeria monocytogenes by size measurement, TEM, and SDS-PAGE analysis. 
The results indicated that 0.5% lactic acid could completely inhibit the growth of Salmonella Enteritidis, E. coli and L. monocytogenes cells. 
Meanwhile, lactic acid resulted in leakage of proteins of Salmonella, E. coli and Listeria cells, and the amount of leakage after 6 h exposure were up to 11.36, 11.76 and 16.29 μg/mL, respectively. 
Measurements of the release of proteins and SDS-PAGE confirmed the disruptive action of lactic acid on cytoplasmic membrane, as well as the content and activity of bacterial proteins. 
The Z-Average sizes of three pathogens were changed to smaller after lactic acid treatment. 
The damaged membrane structure and intracellular structure induced by lactic acid could be observed from TEM images. 
The results suggested that the antimicrobial effect was probably caused by physiological and morphological changes in bacterial cells.


Fifty strains each of Staphylococcus aureus, beta haemolytic Streptococci, Proteus species, Esch coli and Pseudomonas aeruginosa were subjected to 2%, 1 % and 0. 1 % lactic acid in peptorie water. 
Minimum inhibitory concentration of lactic acid for all the strains of each of these organisms was 0.1% or 1%. 
Depending upon its concentration, lactic acid added to peptone water brings down the PH to 2.5-4 which by itself has some inhibitory effect on the microorganisms. 
Lactic acid however, retains its inhibitory effect even if the Ph of the peptone water is brought back to 7.3. 
Lactic acid is a nontoxic and non-sensitizing agent because it is a normal metabolite of the body. 
Thus, it can be used as a safe and effective antibacterial agent for local application.

CLASSIFICATION: Food acidity regulator, Preservative, Plant growth regulator

A normal intermediate in the fermentation (oxidation, metabolism) of sugar. 
The concentrated form is used internally to prevent gastrointestinal fermentation.
Conversion to glucose via gluconeogenesis in the liver and release back into the circulation

Name    DL-Lactic acid
Synonyms    2-Hydroxypropanoic acid
2-Hydroxypropionic acid
Lactic acid
Lactic acid, dl-
Propanoic acid, 2-hydroxy-
(RS)-2-Hydroxypropionsaeure
1-Hydroxyethanecarboxylic acid
AI3-03130
Acidum lacticum
BRN 5238667
CCRIS 2951
Lactovagan
Tonsillosan
alpha-Hydroxypropionic acid
2-hydroxy-2-methylpropanoic acid
(2S)-2-hydroxypropanoate
(2R)-2-hydroxypropanoate
CAS    598-82-3
50-21-5

Lactic acid in Food
Lactic acid is naturally present in many foodstuffs. 
It is formed by natural fermentation in products such as cheese, yogurt, soy sauce, sourdough, meat products and pickled vegetables.

Lactic acid is also used in a wide range of food applications such as bakery products, beverages, meat products, confectionery, dairy products, salads, dressings, ready meals, etc. 
Lactic acid in food products usually serves as either as a pH regulator or as a preservative. 
It is also used as a flavoring agent.

Meat, Poultry & Fish
Lactic acid can be used in meat, poultry and fish in the form of sodium or potassium lactate to extend shelf life, control pathogenic bacteria (improve food safety), enhance and protect meat flavor, improve water binding capacity and reduce sodium.

Beverages
Because of its mild taste, lactic acid is used as an acidity regulator in beverages such as soft drinks and fruit juices.

Pickled vegetables
Lactic acid is effective in preventing the spoilage of olives, gherkins, pearl onions and other vegetables preserved in brine.

Salads & dressings
Lactic acid may be also used as a preservative in salads and dressings, resulting in products with a milder flavor while maintaining microbial stability and safety.

Confectionery
Formulating hard-boiled candy, fruit gums and other confectionery products with lactic acid results in a mild acid taste, improved quality, reduced stickiness and longer shelf life.

Dairy
The natural presence of lactic acid in dairy products, combined with the dairy flavor and good antimicrobial action of lactic acid, makes lactic acid an excellent acidification agent for many dairy products.

Baked Goods
Lactic acid is a natural sourdough acid, which gives the bread its characteristic flavor, and therefore it can be used for direct acidification in the production of sourdough.

Savory Flavors
Lactic acid is used to enhance a broad range of savory flavors. 
Its natural occurrence in meat and dairy products makes lactic acid an attractive way to enhance savory flavors.


Lactic acid in non-food

Pharmaceutical
The primary functions for the pharmaceutical applications are: pH-regulation, metal sequestration, chiral intermediate and as a natural body constituent in pharmaceutical products.

Biomaterials
Lactic acid is a valuable component in biomaterials such as resorbable screws, sutures and medical devices.

Detergents
Lactic acid well known for its descaling properties and is widely applied in household cleaning products. 
Also, lactic acid is used as a natural anti-bacterial agent in disinfecting products.

Technical
Lactic acid is used in a wide variety of industrial processes where acidity is required and where its properties offer specific benefits. Examples are the manufacture of leather and textile products and computer disks, as well as car coating.

Animal Feed
Lactic acid is a commonly used additive in animal nutrition. It has health promoting properties, thus enhancing the performance of farm animals. 
Lactic acid can be used as an additive in food and/or drinking water.
Lactic acid in biodegradable plastics
Lactic Acid is the principal building block for Poly Lactic Acid (PLA). 
PLA is a biobased and bio-degradable polymer that can be used for producing renewable and compostable plastics.


Created by Corbion Purac: the leading supplier of lactic acid, derivatives and lactides

Lactic acid (2-hydroxypropionic acid)
Substance group: Organic acids

Lactic acid is an organic acid occurring naturally in the human body and in fermented foods. 
It is used in a wide range of food, beverages, personal care, healthcare, cleaners, feed & pet food and chemical products as a mild acidity regulator with flavour enhancing and antibacterial properties. 
The commercial production of lactic acid is typically done by fermentation. 
Because the L(+) form is preferred for its better metabolisation, Jungbunzlauer has chosen to produce pure L(+)-lactic acid by traditional fermentation of natural carbohydrates.

L(+)-lactic acid is a colourless to yellowish, nearly odourless, syrupy liquid with a mild acid taste. 
It is commercially available as aqueous solutions of various concentrations. 
These solutions are stable under normal storage conditions.
Lactic acid is non-toxic to humans and the environment, but concentrated solutions of lactic acid can cause skin irritation and eye damage. 
They have thus to be labelled with a hazard pictogram and related statements. Lactic acid is readily biodegradable.

Molecular weight 90.1; colorless crystals. Known D (+) -lactic acid, D (-) -lactic (meat-lactic) acid and racemic lactic acid - fermentation lactic acid. For D, L- and D- lactic acids - melting point, respectively, 18 ° C and 53 ° C; boiling point, respectively, 85 ° C / 1 mm Hg. and 103 ° C / 2mm Hg; for D- lactic acid, the specific optical rotation for the D-line of sodium at a temperature of 20˚C: [α] D 20   -2.26 (concentration 1.24% in water). For D, L -lactic acid ∆H 0 formation - 682.45 kJ / mol; ∆H 0 melting 11.35 kJ / mol; ∆H 0 evaporation 110.95 kJ / mol (25 ° C), 65.73 kJ / mol (150 ° C). For L- lactic acid ∆H 0 combustion - 1344.8 kJ / mol; ∆H 0 formation -694.54 kJ / mol; ∆H 0 melting 16.87 kJ / mol.

Due to the high hygroscopicity of lactic acid, its concentrated aqueous solutions are usually used - syrupy, colorless, odorless liquids. 
For aqueous solutions of lactic acid, the density is g / cm 3 at a temperature of 20˚C d 4 20 1.0959 (40%), 1.1883 (80%), 1.2246 (100%); specific optical rotation for the sodium D-line at a temperature of 25˚С: [α] D 25   1.3718 (37.3%), 1.4244 (88.6%); h 3.09 and 28.5 mPa ∙ s (at 25 ˚С), respectively, for 45.48 and 85.32% solutions; g 46.0.10 -3 N / m (25 ° C) for 1 M solution; e 22 (17 ° C). 
Lactic acid dissolves in water, ethanol, poorly - in benzene, chloroform, and other halogenated hydrocarbons; pK a 3.862 (at 25 ° C); pH of aqueous solutions 1.23 (37.3%), 0.2 (84.0%).

Oxidation of lactic acid is usually accompanied by decomposition. Under the action of HNO 3 or O 2 of air in the presence of Cu or Fe, HCOOH, CH 3 COOH, (COOH) 2 , CH 3 CHO, CO 2 and pyruvic acid are formed. 
Reduction of lactic acid HI leads to propionic acid, and reduction in the presence of Re-mobile leads to propylene glycol.

Lactic acid dehydrates to acrylic acid, when heated with HBr, forms 2-bromopropionic acid, when the Ca salt reacts with PCl 5 or SOCl 2 -2-chloropropionyl chloride . 
In the presence of mineral acids, self-esterification of lactic acid occurs with the formation of lactone, as well as linear polyesters. 
When lactic acid interacts with alcohols, hydroxy acids RCH 2 CH (OH) COOH are formed, and when lactic acid salts react with alcohol esters. 
The salts and esters of lactic acid are called lactates.

Lactic acid is formed as a result of lactic acid fermentation (with sour milk, sauerkraut, pickling vegetables, ripening cheese, ensiling feed); D- lactic acid is found in tissues of animals, plants, and also in microorganisms.

In industry, lactic acid is obtained by hydrolysis of 2-chloropropionic acid and its salts (100 ° C) or lactonitrile CH 3 CH (OH) CN (100 ° C, H 2 SO 4 ), followed by the formation of esters, the isolation and hydrolysis of which leads to a high quality. 
Other methods of producing lactic acid are known: the oxidation of propylene with nitrogen oxides (15-20 ° C) followed by treatment with H 2 SO 4 , the interaction of CH 3 CHO with CO (200 ° C, 20 MPa).

Lactic acid is used in the food industry, in mordant dyeing, in leather production, in fermentation shops as a bactericidal agent, for the production of medicines, plasticizers. Ethyl and butyl lactates are used as solvents for cellulose ethers, drying oils, vegetable oils; butyl lactate - as well as a solvent for some synthetic polymers.

Lactic acid is an organic acid. It has a molecular formula CH3CH(OH)COOH. 
It is white in the solid state and it is miscible 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 (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.

In solution, it can ionize, producing the lactate ion CH3CH(OH)CO−2. 
Compared to acetic acid, its pKa 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, consisting of two enantiomers. 
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. 
A mixture of the two in equal amounts is called dl-lactic acid, or racemic lactic acid. Lactic acid is hygroscopic. 
dl-Lactic acid is miscible with water and with ethanol above its melting point, which is around 16, 17 or 18 °C. 
d-Lactic acid and 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 (R)-lactic acid. On the other hand, lactic acid produced by anaerobic respiration in animal muscles has the (S) configuration and is sometimes called "sarcolactic" acid, from the Greek "sarx" for flesh.

In animals, l-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise.
It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal, which is governed by a number of factors, including monocarboxylate transporters, concentration and isoform of LDH, and oxidative capacity of tissues.
The concentration of blood lactate is usually 1–2 mM 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, l-lactic acid is the primary endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA1), which is a Gi/o-coupled G protein-coupled receptor (GPCR).[10][11]

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 caries.
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.

History
Swedish chemist Carl Wilhelm Scheele was the first person to isolate lactic acid in 1780 from sour milk.
The name reflects the lact- combining form derived from the Latin word lac, which means milk. 
In 1808, Jöns Jacob Berzelius discovered that lactic acid (actually l-lactate) also is produced in muscles during exertion.
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.

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 of carbohydrates, or by chemical synthesis from acetaldehyde.
In 2009, lactic acid was produced predominantly (70–90%)[20] by fermentation. Production of racemic lactic acid consisting of a 1:1 mixture of d and l stereoisomers, or of mixtures with up to 99.9% l-lactic acid, is possible by microbial fermentation. 
Industrial scale production of d-lactic acid by fermentation is possible, but much more challenging.

Fermentative production
Fermented milk products are obtained industrially by fermentation of milk or whey by Lactobacillus bacteria: Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii subsp. bulgaricus (Lactobacillus bulgaricus), Lactobacillus helveticus, Lactococcus lactis, and Streptococcus salivarius subsp. thermophilus (Streptococcus thermophilus).

As a starting material for industrial production of lactic acid, almost any carbohydrate source containing C5 and C6 sugars 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.
Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials (vinyl acetate, glycerol, etc.) by application of catalytic procedures.

Biology
Molecular biology
l-Lactic acid is the primary endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA1), a Gi/o-coupled G protein-coupled receptor (GPCR).

Exercise and lactate
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.

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; see Cori cycle
If blood glucose concentrations are high, the glucose can be used to build up the liver's glycogen stores.
However, lactate is continually formed even at rest and during moderate exercise. Some causes of this are metabolism in red blood cells that lack mitochondria, and limitations resulting from the enzyme activity that occurs in muscle fibers having high glycolytic capacity.[25]

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− + HPO2−
4 + H+), and that reducing pyruvate to lactate (pyruvate− + NADH + H+ → lactate− + NAD+) actually consumes H+.
Lindinger et al.[27] countered that they had ignored the causative factors of the increase in [H+]. 
After all, the production of lactate− from a neutral molecule must increase [H+] 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+:

C6H12O6 + 2 NAD+ + 2 ADP3− + 2 HPO2−4    →    2 CH3COCO−2 + 2 H+ + 2 NADH + 2 ATP4− + 2 H2O
Subsequent lactate− production absorbs these protons:
2 CH3COCO−2 + 2 H+ + 2 NADH    →    2 CH3CH(OH)CO−2 + 2 NAD+

Overall:
C6H12O6 + 2 NAD+ + 2 ADP3− + 2 HPO2−4    →    2 CH3COCO−2 + 2 H+ + 2 NADH + 2 ATP4− + 2 H2O→    2 CH3CH(OH)CO−2 + 2 NAD+ + 2 ATP4− + 2 H2O
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− + HPO2−
4 + H+. So once the use of ATP is included, the overall reaction is

C6H12O6 → 2 CH3COCO−2 + 2 H+

The generation of CO2 during respiration also causes an increase in [H+].

Metabolism
Although glucose is usually assumed to be the main energy source for living tissues, there are some indications that it is lactate, and not glucose, that is preferentially metabolized by neurons in the brain of several mammalian species (the notable ones being mice, rats, and humans).
According to the lactate-shuttle hypothesis, glial 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 immediately surrounding neurons strongly differs in composition from the blood or cerebrospinal fluid, being much richer with lactate, as was found in microdialysis studies.

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.
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,acting either through better support of metabolites, or alterations in base intracellular pH levels,or both.

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.
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.[16]

Blood testing

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[38]    19.8[38]    mg/dL
0.5[39]    2.2[39]    mmol/L
Arterial    4.5[38]    14.4[38]    mg/dL
0.5[39]    1.6[39]    mmol/L
During childbirth, lactate levels in the fetus can be quantified by fetal scalp blood testing.

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 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.

Foods
Lactic acid is found primarily in sour milk products, such as koumiss, laban, yogurt, kefir, and some cottage cheeses. 
The casein in fermented milk is coagulated (curdled) by lactic acid. 
Lactic acid is also responsible for the sour flavor of 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.[40] If this is the case then the calculated food energy may use the standard 4 kilocalories (17 kJ) 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 362 kilocalories (1,510 kJ) per 100 g.

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.

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.

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.

As a food additive it is approved for use in the EU, USA and Australia and New Zealand; 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.
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.

Cleaning products
Lactic acid is used in some liquid cleaners as a descaling agent for removing hard water deposits such as calcium carbonate, forming the lactate, 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.


PRODUCT INFORMATION
Lactic acid is a hydroxycarboxylic acid CH3CH(OH)COOH with two stereoisomers (D(-) and L(+)) and it has several applications in food, chemical, pharmaceutical and health care industries. 
It is primarily used for food and pharmaceutical applications, preferentially the L(+) isomer, since it is the only lactic acid isomer produced in the human body. 
Around 20 to 30% of the lactic acid production is used to obtain biopolymers (polylactic acid). 
Other uses include fibers and green solvents.

Lactic acid is fully commercially available and largely (90%) produced by bacteria through anaerobic fermentation of sugars. 
It can also be commercially produced by chemical synthesis. 
The chemical production pathway gives an optical inactive racemic mixture (with the same quantity of L and D isomers), while the anaerobic fermentation pathway mostly yieldsone of the two stereoisomers, depending on the microorganism chosen. 
The biotechnological option is widely available due to its renewable origin. 
Lactic acid can be produced via fermentation of sugars from different biomass, such as: starch crops, sugar crops, lignocellulosic materials and also from whey (a residue from cheese production). 

The bulk of world production is based on homoplastic fermentation of sugars (from starch or sugar crops) where lactic acid is produced as sole product. 
Conventional production systems require the addition of calcium hydroxide to control the fermentation pH. 
This procedure results in calcium lactate as final product. 
Several steps are required to ultimately obtain and purify lactic acid: filtration, acidification, carbon adsorption, evaporation, esterification, hydrolysis and distillation. 
The conventional process is associated with high costs (due to the complex purification procedure) and poor environmental performance due to the production of large amounts of chemical effluents (e.g. calcium sulphate). 
New separation technologies are being developed, such as bipolar electrodialysis with promising results.

Lactic acid, the most fundamental natural ingredient in the dairy industry
In dairy products, lactic acid is one of the most common ingredients. 
Its purpose is generally as an acid regulator and in terms of flavouring. 
The slightly sour taste observed in yogurts, cheeses and other milk products is generally the result of fermentation from lactic acid. 
The signature flavour of sourdough bread is also a result of lactic acid during the baking process. 
With the addition of this versatile supplement, the product can be acidified with ease to reach proper pH levels, while leaving the natural flavours undisturbed. 

2-hydroxypropanoic acid

DL-Lactic acid

50-21-5

2-hydroxypropionic acid


Molecular Weight    
90.08 g/mol


Lactic Acid, DL- is the racemic isomer of lactic acid, the biologically active isoform in humans. 
Lactic acid or lactate is produced during fermentation from pyruvate by lactate dehydrogenase. 
This reaction, in addition to producing lactic acid, also produces nicotinamide adenine dinucleotide (NAD) that is then used in glycolysis to produce energy source adenosine triphosphate (ATP).

NCI Thesaurus (NCIt)
Lactic acid appears as a colorless to yellow odorless syrupy liquid. Corrosive to metals and tissue. Used to make cultured dairy products, as a food preservative, and to make chemicals.


A normal intermediate in the fermentation (oxidation, metabolism) of sugar. 
The concentrated form is used internally to prevent gastrointestinal fermentation. 
Sodium lactate is the sodium salt of lactic acid, and has a mild saline taste. 
It is produced by fermentation of a sugar source, such as corn or beets, and then, by neutralizing the resulting lactic acid to create a compound having the formula NaC3H5O3. 
Lactic acid was one of active ingredients in Phexxi, a non-hormonal contraceptive agent that was approved by the FDA on May 2020.


2-hydroxypropanoic acid


Lactic acid

2 Hydroxypropanoic Acid
2 Hydroxypropionic Acid
2-Hydroxypropanoic Acid
2-Hydroxypropionic Acid
Ammonium Lactate
D Lactic Acid
D-Lactic Acid
L Lactic Acid
L-Lactic Acid
Lactate
Lactate, Ammonium
Lactic Acid
Propanoic Acid, 2-Hydroxy-, (2R)-
Propanoic Acid, 2-Hydroxy-, (2S)-
Sarcolactic Acid


2-hydroxypropanoic acid
DL-Lactic acid
50-21-5
2-hydroxypropionic acid
Milk acid
Polylactic acid
lactate
Ethylidenelactic acid
Lactovagan
Tonsillosan
Racemic lactic acid
Propanoic acid, 2-hydroxy-
Ordinary lactic acid
Milchsaeure
Acidum lacticum
Kyselina mlecna
DL-Milchsaeure
Lactic acid USP
1-Hydroxyethanecarboxylic acid
Aethylidenmilchsaeure
alpha-Hydroxypropionic acid
Lacticacid
Lactic acid (natural)
FEMA No. 2611
26100-51-6
Kyselina 2-hydroxypropanova
Milchsaure [German]
Propionic acid, 2-hydroxy-
598-82-3
(RS)-2-Hydroxypropionsaeure
CCRIS 2951
HSDB 800
(+-)-2-Hydroxypropanoic acid
FEMA Number 2611


Kyselina mlecna [Czech]
propanoic acid, hydroxy-
SY-83
DL- lactic acid
Propel
NSC 367919
AI3-03130

Purac FCC 80

Purac FCC 88

Kyselina 2-hydroxypropanova [Czech]

EINECS 200-018-0

EINECS 209-954-4

MFCD00004520

EPA Pesticide Chemical Code 128929
BRN 5238667
(R)-2-Hydroxy-propionic acid;H-D-Lac-OH
CHEBI:78320
Poly(lactic acid)
C3H6O3
NSC-367919
NCGC00090972-01
2-hydroxy-propionic acid
DL-Lactic acid, 90%
E 270
DSSTox_CID_3192
(+/-)-Lactic acid
alpha-Hydroxypropanoic acid

C01432
DSSTox_RID_76915
DSSTox_GSID_23192
Milchsaure
Polactide
Lacticum acidum
D(-)-lactic acid
Cheongin samrakhan
UNII-3B8D35Y7S4
CAS-50-21-5
Cheongin Haewoohwan
Cheongin Haejanghwan
Lactic acid [JAN]
Lactic acid [USP:JAN]
lactasol
Propanoic acid, 2-hydroxy-, homopolymer
1-Hydroxyethane 1-carboxylic acid
Biolac
Whey

Acid lactic (ro)
Acide lactique (fr)
Acido lattico (it)
Aċidu lattiku (mt)
Kwas mlekowy (pl)
Kyselina mliečna (sk)
Kyselina mléčná (cs)
Lactic acid (no)
Maitohappo (fi)
Melkzuur (nl)
Milchsäure (de)
Mjölksyra (sv)
Mlečna kislina (sl)
Mliječna kiselina (hr)
Mælkesyre (da)
Pieno rūgštis (lt)
Pienskābe (lv)
Piimhape (et)
Tejsav (hu)
Ácido láctico (es)
Ácido láctico (pt)
Γαλακτικό οξύ (el)
Млечна киселина (bg)

CAS names
Propanoic acid, 2-hydroxy-


IUPAC names
2- Hydroxy propanoic acid
2-HYDROXY-PROPANOIC ACID
2-hydroxy-propanoic acid
2-Hydroxypropanoic Acid
2-Hydroxypropanoic acid
2-hydroxypropanoic acid
2-Hydroxypropionic acid
2-hydroxypropionic acid
D-LACTIC ACID
DL-Lactic Acid
dl-lactic acid
LACTIC ACID
Lactic Acid
Lactic acid
lactic acid
Lactic acid
lactic acid
Milchsäure
Propanoic acid, 2-hydroxy-
Propanoic acid,2-hydroxy-
Tejsav

Lactic Acid Derivatives as Food AdditivesLactic acid is surely important in the food industry. 
On the other hand, severaldifferent additives are chemically derived from lactic acid


actic acid (chemically, alpha or 2-Hydroxypropionic acid) takes roles in metabolic processes in the body; in red blood and in skeletal muscle tissues as a product of glucose and glycogen metabolism. 
Lactic acid is an "alpha hydroxy acid: which has a hydroxyl group on the carbon atom next to the acid group. 
If the hydroxy group is on the second carbon next to the acid group, it is called beta-hydroxy acid. 
Lactic acid is converted in vivo to pyruvic acid (an alpha keto acid) which occurs as an intermediate product in carbohydrate and protein metabolism in the body. 
Lactic acid occurs as two optical isomers since the central carbon atom is bound to four different groups; a dextro and a levo form ( or an inactive racemic mixture of the two); only the levo form takes part in animal metabolism. Lactic acid is present  in sour milk and dairy products such as cheese, yogurt, and  koumiss, leban, wines.  
Lactic acid causes tooth decay since lactic acid bacteria operates in the mouth. 
Although it can be prepared by chemical synthesis, production of lactic acid by fermentation of glucose and other sugar substances in the presence of alkaline such as lime or calcium carbonate is a less expensive method. 
The six-carbon glucose molecule is broken down to two molecules of the three-carbon compounds (lactic acid), during this anaerobic condition. 
Synthetic lactic acid is used commercially in tanning leather and dyeing wool; as a flavouring agent and preservative in food processing and carbonated beverages; and as a raw material in making plastics, solvents, inks, and lacquers; as a catalyst in numerous chemical processes. 
Lactic Acid is available as aqueous solutions of various concentrations, usually 22 - 85 percent (pure lactic acid is a colourless, crystalline substance.) 
Some examples of lactates (salts or esters of lactic acid) are:

Ammonium Lactate (NH4C3H5O3, CAS RN: 515-98-0): clear to yellow, syrupy liquid used in in electroplating, in finishing leather and as humectant for food, pharmaceutical, and cosmetics.
Butyl Lactate (CH3CHOHCOOC4H9, CAS RN:138-22-7): a clear liquid: nontoxic, miscible with many solvents; used as a solvent for varnish, lacquers, resins and gums, used in making paints, inks, dry cleaning fluid, flavoring and as a chemical intermediate.
Calcium Lactate Pentahydrate [Ca(C3H5O3)2·5H2O, CAS RN: 814-80-2] : white crystals; soluble in water; used as a calcium source; administered orally in the treatment of calcium deficiency; as a blood coagulant.
Ethyl Lactate   (CH3CHOHCOOC2H5, CAS RN: 97-64-3): clear liquid with mild odur; boiling point 154 C; miscible with alcohols, ketones, esters, and hydrocarbons as well as with water; used in pharmaceutical preparations, feed additive, as a flavoring ( odor description: sweet butter, coconut, fruity, creamy dairy, butterscotch) and as a solvent for cellulose compounds such as nitrocellulose, cellulose acetate, and cellulose ethers.
Magnesium Lactate Trihydrate [Mg(C3H5O3)2·3H2O, CAS RN: 18917-93-6 ]: white crystals with bitter taste; soluble in water, slightly soluble in alcohol; used in medicine and as an electrolyte replenisher.
Manganese Lactate Trihydrate [Mn(C3H5O3)2·3H2O]: pale red crystals; insoluble in water and alcohol; used in medicine.
Mercuric Lactate [Hg(C3H5O3)2]: poisonous white powder that decomposes when heated; soluble in water; used in medicine.
Methyl Lactate (CH3CHCHCOOCH3): clear liquid with mild odur; boiling point 145 C; miscible with alcohols, ketones, esters, and hydrocarbons as well as with water; used in pharmaceutical preparations, feed additive, as a flavoring and as a solvent for cellulose compounds such as nitrocellulose, cellulose acetate, and cellulose ethers.
Sodium Lactate (CH3CHOHCOONa, CAS RN: 72-17-3) clear to yellow, hygroscopic syrupy liquid; soluble in water; melting point 17 C; used in medicine, in antifreeze, and hygroscopic agent and as a corrosion inhibitor.
Zinc Lactate (Zn(C3H5O3)2·2H2O, CAS RN: 16039-53-5): white crystals; used as an additive in toothpaste and food; preparation of drugs.


This Brief explores the importance of lactic acid and fermentation in the modern food industry. 
Although it is usually associated with milk and dairy products, lactic acid can also be found in many other fermented food products, including confectionery products, jams, frozen desserts, and pickled vegetables. 
In this work, the authors explain how lactic acid is produced from lactose by Lactobacillus and Streptococcus cultures, and they also emphasise its important role as pH regulator and preservative, helping to the inhibition of microbial growth in fermented foods. 
The Brief discusses a wide range of lactic acid’s applications as a natural additive, curing or gelling agent, flavour, food carrier, solvent, and discoloration inhibitor, among others. 


The most important category of lactic acid derivatives with possible foodapplications is certainly the group of ‘lactic and fatty acid esters of glycerol’,according to the GSFA. This group of fatty esters may be used in many foodproductions with three main purposes (Codex Alimentarius Commission 1995):

(a) Emulsification(b) Sequestration(c) Stabilisation.
The use of lactic esters as emulsifying and surface active agents is well known.Mono- and diglycerides esterified with lactic acid are powerful emulsifiers. 
A goodexample can be stearyl-2-lactylate, obtained from stearic acid and lactic acid inalkaline solution (Belitz et al. 2009). 
Obtained lactylates are mainly represented bycalcium or sodium stearyl-2-lactylate, depending on the used alkaline agent (cal-cium or sodium hydroxide).
Because of the chemical relationship with lactic acid, these compounds are recommended with these objectives in some of food categories already shown forlactic acid, including pasteurised cream (plain); sterilised creams; fresh pastas,noodles and similar foods; salt substitutes Interestingly, a maximum limit of 5000 gper kg is recommended when speaking of the category 13.2 ‘complementary foodsfor infants and young children’; a different and non-GMP limited values have beendecided for lactic acid also in this ambit. 
All remaining food categories do not showsimilar limitations (Codex Alimentarius Commission 1995).


Lactic acid bacteria (LAB) are heterogenous group of bacteria which plays a significant role in a variety of fermentation processes. 
They ferment food carbohydrates and produce lactic acid as the main product of fermentation. In addition, degradation of proteins and lipids and production of various alcohols, aldehydes, acids, esters and sulphur compounds contribute to the specific flavour development in different fermented food products.

The main application of LAB is as starter cultures, with an enormous variety of fermented dairy (ie. cheese, yoghurt, fermented milks), meat, fish, fruit, vegetable and cereal products. Besides, they contribute to the flavour, texture and nutritional value of the fermented foods, and thus they are used as adjunct cultures. 
Acceleration of cheese maturation, enhancement of yoghurt texture with the production of exo polysaccharides and control of secondary fermentations in the production of wine are some examples. The production of bacteriocins and antifungal compounds has lead to the application of bio-protective cultures in certain foods. 
Moreover, the well-documented health-promoting properties of certain LAB have lead to the addition of selected strains, in combination with bifidobacteria, as probiotic cultures with various applications in food industry.

Keywords: lactic acid bacteria, applications, fermented foods

Introduction
Lactic acid bacteria (LAB) play an important role in food, agricultural, and clinical applications. 
The general description of the bacteria included in the group is gram-positive, nonsporing, nonrespiring cocci or rods, which produce lactic acid as the major end product during the fermentation of carbohydrates.
The common agreement is that there is a core group consisting of four genera; Lactobacillus, Leuconostoc, Pediococcus and Streptococcus. 
Recent taxonomic revisions have proposed several new genera and the remaining group now comprises the following: Aerococcus, Alloiococcus, Carnobacterium, Dolosigranulum, Enterococcus, Globicatella, Lactococcus, Oenococcus, Tetragenococcus, Vagococcus, and Weissella.
Their importance is associated mainly with their safe metabolic activity while growing in foods utilising available sugar for the production of organic acids and other metabolites. Their common occurrence in foods along with their long-lived uses contributes to their natural acceptance as GRAS (Generally Recognised as Safe) for human consumption.3 The EFSA’s ‘Panel on Biological Hazards (BIOHAZ)’ has concluded that for the fermenting bacteria associated with food, whether resistant to antibiotics or not - with the possible exception of enterococci - there is no evidence for any clinical problem.4 However, they can act as a reservoir for transferable resistance genes. Strains with genes transferable in such a way could inter the food chain and increase the probability of a transfer to food associated intestinal pathogenic organisms.

The three main pathways which are involved in the manufacture and development of flavour in fermented food products are as follows:
1) glycolysis (fermentation of sugars)
2) lipolysis (degradation of fat) and 
3) proteolysis (degradation of proteins)

1,5−9 Lactate is the main product generated from the metabolism of carbohydrates and a fraction of the intermediate pyruvate can alternatively be converted to diacetyl, acetoin, acetaldehyde or acetic acid (some of which can be important for typical yogurt flavours). 
The contribution of LAB to lipolysis is relatively little, but proteolysis is the key biochemical pathway for the development of flavour in fermented foods.
Degradation of such components can be further converted to various alcohols, aldehydes, acids, esters and sulphur compounds for specific flavour development in fermented food products.

The genetics of the LAB have been reviewed12−18 and complete genome sequences of a great number of LAB have been published19 since 2001, when the first genome of LAB (Lactococcus lactis ssp. lactis IL1403) was sequenced and published.

Applications of LAB
Starter cultures for fermented foods

Fermented foods are produced through fermentation of certain sugars by LAB and the origins of them are lost in antiquity. 
The most commonly LAB used as starter cultures in food fermentations are shown in Table 1. It is well-known that the greatest proportion of them belong to the category of dairy products, namely cheese, yoghurt, fermented milks, while fermented meat products, fish products, pickled vegetables and olives and a great variety of cereal products are manufactured, nowadays, using starter cultures. These products, were produced in the past through back slopping and the resulting product characteristics depended on the best-adapted strains dominance, whereas, the earliest productions of them were based on the spontaneous fermentation, resulting from the development of the microflora naturally present in the raw material and its environment. Today, the majority of fermented foods are manufactured with the addition of selected, well defined, starter cultures with well characterized traits, specific for each individual product. For a detailed classification of starter cultures see.21−23

Adjunct cultures

Secondary cultures, or adjunct cultures or adjuncts, are defined as any cultures that are deliberately added at some point of the manufacture of fermented foods, but whose primary role is not acid production. 
Adjunct cultures are used in cheese manufacture to balance some of the biodiversity removed by pasteurisation, improved hygiene and the addition of defined-strain starter culture.
These are mainly non-starter LAB which have a significant impact on flavour and accelerate the maturation process.

Extracellular polysaccharides (EPSs) are produced by a variety of bacteria and are present as capsular polysaccharides bound to the cell surface, or are released into the growth medium.
These polymers play a major role in the production of yogurt, cheese, fermented cream and milk-based desserts where they contribute to texture, mouth-feel, taste perception and stability of the final products. 
In addition, it has been suggested that these EPSs or fermented milks containing these EPSs are active as prebiotics, cholesterol-lowering and immunomodulants. 
EPS-producing strains of Streptococcus thermophilus and Lactobacillus delbreuckii ssp. bulgaricus have been shown to enhance the texture and viscosity of yogurt and to reduce syneresis.

For the production of wine, LAB are involved in the malolactic fermentation, that is a secondary fermentation, which involves the conversion of L-malate to L-lactate and CO2 via malate decarboxylase, also known as the malolactic enzyme, resulting in a reduction of wine acidity, providing microbiological stabilization and modifications of wine aroma.

Bio-protective cultures

Certain LAB have been found to produce bacteriocins, namely, polypeptides synthesized ribosomally by bacteria that can have a bacteriocidal or bacteriostatic effect on other bacteria.
In general, bacteriocins lead to cell death by inhibiting cell wall biosynthesis or by disrupting the membrane through pore formation.
Bacteriocins are therefore important in food fermentations where they can prevent food spoilage or the inhibition of food pathogens. The best known bacteriocin is nisin, which has gained widespread application in the food industry and is used as a food additive in at least 50 countries, particularly in processed cheese, dairy products and canned foods.
Examples of useful bacteriocins produced by LAB are lacticin 314738−41 from lactococci, macedovicin from Streptococcus macedonicus ACA-DC 198,42,43 reuterin from Lactobacillus reuteri, sakacin M from Lactobacillus sake 14845 curvacin A, curvaticin L442 and lactocin AL705 from Lactobacillus curvatus LTH1174,46 pediocin PA-1/AcH from Pediococcus acidilactici,47 plantaricins (A, EF and JK) from Lactobacillus plantarum.
The above bacteriocins have proved effective in many food systems for the control of food spoilage or pathogenic bacteria.

Antifungal activities of LAB have been reported.48−50 In addition; LAB strains also have the ability to reduce fungal mycotoxins, either by producing anti-mycotoxinogenic metabolites, or by absorbing them.50

For LAB to be used as bio-protective starter cultures, they must possess a range of physical and biochemical characteristics, and most importantly, the ability to achieve growth and sufficient production of antimicrobial metabolites, which must be demonstrated in the specific food environment.

Probiotic culture

LAB are considered as a major group of probiotic bacteria; probiotic has been defined by Fuller as "a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance". 
Salminen et al.54 proposed that probiotics are microbial cell preparations or components of microbial cells that have a beneficial effect on the health and well-being of the host. 
Commercial cultures used in food applications include mainly strains of Lactobacillus spp., Bifidobacterium spp. and Propionibacterium spp. Lactobacillus acidophilus, Lactobacillus casei, Lb. reuteri, Lactobacillus rhamnosus and Lb. plantarum are the most used LAB in functional foods containing probiotics.
Argentinean Fresco cheese, Cheddar and Gouda are some examples of applications of probiotic LAB, in combination with bifidobacteria, in cheeses.

The health-promoting effects of LAB are shown in Table 2. 
Apparently, these effects are species and strain specific, and the big challenge is the use of probiotic cultures composed of multiple species.
In addition, LAB, as part of gut microbiota ferment various substrates such as biogenic amines and allergenic compounds into short-chain fatty acids and other organic acids and gases.

In recent years, the genomes of several probiotic species have been sequenced, thus paving the way to the application of ‘omics’ technologies to the investigation of probiotic activities.
Moreover, although recombinant probiotics have been constructed, the industrial application of genetically engineered bacteria is still hampered by legal issues and by a rather negative general public opinion in the food sector.

Product
Genera of LAB1

Reference

Dairy products
Cheese (Mesophilic starter)
Lc. lactis ssp. lactis

22

Lc. lactis ssp. cremoris

Lc. lactis ssp. lactis var. diacetylactis

Leuc. mesenteroides ssp. cremoris

Cheese (Thermophilic starter)

S. thermoplillus

22

Lb. delbrueckii ssp. bulgaricus

Lb. helveticus

Lb. delbrueckii ssp. lactis

Cheese (Mixed starter)

Lc. lactis ssp. lactis

22

Lc. lactis ssp. cremoris

S. thermoplillus

Yogurt

Lb. delbrueckii ssp. bulgaricus,
S. thermophilus

22

Fermented milks

Lb. delbrueckii ssp. bulgaricus, S. thermophilus Lb. casei,
Lb. acidophilus, Lb. rhamnosus, Lb. johnsonii

22

Yakult

Lb. casei ssp. casei

22

Acidophilus milk

Lb. acidophilus

22

Butter and buttermilk

Lc. lactis ssp. lactis, Lc. lactis ssp. lactis var. diacetylactis,
 Lc. lactis ssp. cremoris, Leuc. menesteroides ssp. cremoris

22

Kefir

Lb. kefir, Lb. kefiranofacies, Lb. brevis, Lb. plantarum,
Lb. paracasei spp. paracasei, Lc. lactis spp. lactis,
Leuc. mesenteroides

62

Trahanas

Lc. lactis ssp. lactis, Lc. lactis ssp. lactis var. diacetylactis, Leuc. menesteroides ssp. cremoris, Lb. delbrueckii ssp. lactis, Lb. casei,
Lb. delbrueckii ssp. bulgaricus and Lb. Acidophilus

63

Fermented meat products

Dry sausages

Lb. sakei, Lb. curvatus, Lb. plantarum, Lb. pentosus, Lb. casei,
P. pentosaceous, P. acidilactici

64,65

Salami Milano

Lb. sakei, Lb. plantarum

66

Salame Piacentino

Lb. acidophilus, Lb. helveticus, Lb. sakei, Lb. antri, Lb. oris, Lb. vaginalis, Lb. brevis, Lb. panis, Lb. versmoldensis, Lb. zeae, Lb. curvatus, Lb. paralimentarius, Lb. frumenti, Lb. plantarum, Lb. graminis, Lb. reuteri

67

Greek dry fermented sausages

Lb. sakei, Lb. plantarum, Lb. curvatus, Lb. pentosus, Lc.
lactis ssp. lactis, W. hellenica, W. paramesenteroides,
W. viridescens, W. minor

67

Chrorizo

Lb. brevis, Lb. curvatus, Lb. sakei, Lc. lactis, P. acidilactici,
P. pentosaceus, Leuc. mesenteroides

67

Fermented fish products

Thai fish

Lb. plantarum, Lb. reuteri

68

Pickled fruits and vegetables

Cabbage (Sauerkraut)

Leuc. mesenteroides, Lb. plantarum, Lb. brevis,
Lb. fermentum

69

Cucumber

Lb. brevis, Lb. plantarum, Lb. pentosus, Lb. acidophilus,
Lb. fermentum, Leuc. Mesenteroides

70,71

Olives

Lb. brevis, Lb. plantarum, Lb. pentosus

72,73

Fermented cereal products

Sourdough

Lb. brevis, Lb. hilgardii

74,75

Lb. sanfransiscensis, Lb. farciminis, Lb. fermentum,
Lb. brevis, Lb. plantarum, Lb. amylovorus, Lb. reuteri,
Lb. pontis, Lb. panis, Lb. alimentarius, W. cibaria

Kimchi

Leuc. mesenteroides, Lb. plantarum, W. kimchii sp. nov.,
Lb. kimchi, Lb. sakei, W. koreensis

76–78

Bushera

Lb. plantarum, Lb. paracasei ssp. paracasei, Lb. fermentum,
 Lb. brevis, Lb. delbrueckii ssp. delbrueckii, S. thermophilus

79

Pozol

Leuc. mesenteroides, Lb. plantarum, Lb. confusus, Lc. lactis, Lc. raffinolactis

80

Table 1 Lactic acid bacteria used as starter cultures in the production of some fermented food products

Lc. Lactococcus, Lb. Lactobacillus, Leuc. Leuconostoc, P. Pediococcus, S. Streptococcus, W. Weissella

Probiotic effect

Reference

Assimilation of cholesterol

 79,80

Lactose intolerance

 79–81

Control viral, bacterial and antibiotic associated diarrheal diseases

 79,80,83–85

Inflammatory bowel disease

 79

Allergies and atopic dermatitis

 86,87

Colonic carcinogens

88,89

Control of pathogenic bacteria

 91,92

Stimulation of the immune system on the gut mucosal surface

93

Table 2 Effects of probiotics on the human health

Conclusion
LAB are the most commonly used microorganisms for the fermentation and preservation of foods. 
Their importance is associated mainly with their safe metabolic activity while growing in foods utilising available sugar for the production of organic acids and other metabolites.

Advances in the genetics, molecular biology, physiology, and biochemistry of LAB have provided new insights and applications for these bacteria. 
Bacterial cultures with specific traits have been developed during the last 17 years, since the discovery of the complete genome sequence of Lc. lactis ssp. lactis IL1403 and a variety of commercial starter, functional, bio-protective and probiotic cultures with desirable properties have marketed.

However, the great challenge for food industry is to produce multiple strain cultures with multiple functions for specific products from specific regions of the world. 
Also it is a challenge to produce foods, which are similar in sensory characteristics and nutritional value to the traditional products, even with special health-promoting properties, in a standardized, safe and controlled process.


Lactic Acid and Lactate
Lactic acid is a weak acid, which means that it only partially dissociates in water. Lactic acid dissociates in water resulting in ion lactate and H+. 
This is a reversible reaction and the equilibrium is represented below.

CH3CH(OH)CO2H  H+ + CH3CH(OH)CO2-Ka= 1.38 x 10-4
Depending on the environmental pH, weak acids such as lactic acid are either present as the acid in its undissociated form at low pH or as the ion salt at higher pH. 
The pH at which 50% of the acid is dissociated is called the pKa, which for lactic acid is 3.86.

Under physiological circumstances the pH is generally higher than the pKa, so the majority of lactic acid in the body will be dissociated and present as lactate. 
In the undissociated (unionized) form the substrates are able to pass through the lipid membranes, unlike the dissociated (ionized) form which cannot.


Lactic acid (2-hydroxypropionic acid) is one of the large-scale chemical that is produced via fermentation. 
The commonly used feedstocks are carbohydrates obtained from different sources like corn starch, sugarcane, or tapioca starch – depending on local availability. 
The carbohydrates are hydrolyzed into monosaccharides and then fermented under the absence of oxygen by microorganisms into lactic acid. 
Lactic acid is the building block for polylactic acid, but it is also used in a broad variety of food and cosmetic applications. 
Bio-based lactic acid is optically active, and the production of either l-(+)- or d-(–)-lactic acid can be directed with bioengineered microorganisms.


Lactic acid (2-hydroxypropionic acid) ranks among the high-volume chemicals produced microbially, with an annual world production volume in the range of 370 000 MT. 
Lactic acid fermentation is among the oldest industrial fermentations, with industrial production via fermentation starting in the 1880s. 
Seventy-five percent of the current world lactic acid production occurs in the fermentation facilities of Galactic, PURAC Corporation, Cargill Incorporated, Archer Daniels Midland Company, and the joint ventures derived from these companies. 
Historically, the primary use of lactic acid has been in food for acidulation and preservation, and it has been granted GRAS (generally recognized as safe) status by the FDA. 
Lactic acid also finds uses in leather tanning, cosmetics, pharmaceutical applications, as well as various other niches [2–4]. World lactic acid production has expanded 10-fold in the last decade due, in large part, to increased demand for green products derived from lactic acid, including ethyl lactate and polylactic acid (PLA). 
Ethyl lactate can be utilized in a variety of green solvents, and although its low human toxicity relative to hydrocarbon alternatives is attractive, price is cited as the primary reason for its limited market use. 
PLA is a polymer that is considered a green alternative to petroleum-derived plastics due to its biodegradability and reduced carbon footprint. 
PLA products are on the market in a wide range of applications including packaging, fibers, and foams. 
The world’s major producer of PLA is NatureWorks LLC, currently wholly owned by Cargill Incorporated. 
The primary cost in the production of PLA and ethyl lactate is the cost of raw material, that is, lactic acid. 
The key parameters that determine the cost of lactic acid are rate, titer, and yield, in both fermentation and downstream product recovery unit operations. 
Furthermore, lactic acid production accounts for a large fraction of the energy input and greenhouse gas (GHG) emissions in lactic acid-derived products. 
These carbon costs can be of great concern in the marketing and viability of a green product.

As discussed previously, lactic acid production has occurred for over 100 years, with only modest changes to conditions or host organisms. 
Lactic acid is produced via fermentation, traditionally carried out by bacteria belonging to the genera Lactobacillus, Lactococcus, Streptococcus, Bacillus, and Enterococcus. 
For the recent applications of lactic acid as a green chemical intermediate, for example, for PLA, the cost of production via traditional process is too high. 
Cost estimates suggest that to be commercially viable, overall lactic acid production costs should be at or below $1.0 per kilogram of lactic acid. 
As a result, a production strain for industrial lactic acid must fit the following criteria: production of > 100 g l−1 lactic acid at yields near theoretical (0.9 g lactic acid per gram of dextrose), high chiral purity of lactic acid produced (> 99%) with rates, media, and recovery costs able to meet the above cost targets. 
Lowering this production cost holds the potential to expand the market for both lactic acid and its green derivatives.

The primary costs associated with fermentation are the nutrients and sugars required for cell growth and lactic acid production along with the downstream recovery and purification process [7]. In addition to a sugar source, traditional bacterial lactic fermentations typically require an organic nitrogen source (such as yeast extract or corn steep liquor) along with B vitamin supplementation. 
Furthermore, these fermentations require that the pH be maintained in the range of 5–7, well above the pKa of lactic acid. 
Maintaining the pH in this range requires neutralization of the lactic acid during fermentation, followed by costly downstream steps or acidulation to regenerate free lactic acid. 
This greatly increases the cost of fermentation.

In 2008, Cargill implemented a new-to-the-world fermentation technology involving genetically modified yeast capable of producing lactic acid at industrially relevant rates, titers, and yields at pH values ≤ 3.0, which is well below the pKa of lactic acid. 
The low-pH fermentation process results in improved product quality and downstream processing, reduced chemical usage and nutrient costs, and a 35% reduction in the GHG emissions associated with lactic acid production by fermentation. 
Additionally, the potential for product loss due to bacteriophage attacks and microbial contamination that can occur in the traditional bacterial process are eliminated or greatly reduced with the low-pH yeast process. 
This increased process robustness contributes to reduction in the overall cost of lactic acid production and subsequently has helped to grow the market for lactic acid and its derivatives.

Future advances in the low-pH yeast process are expected to lower the cost of lactic acid production even more by reducing the cost of the carbon source fermented to lactic acid. 
To achieve this, low-pH yeasts need to be further developed to efficiently ferment low-cost carbon sources to free lactic acid. 
It was estimated by life cycle analysis that through the use of cellulosic feedstocks derived from biomass and the use of wind power to produce lactic acid and PLA, the overall GHG emissions could be calculated as a net negative


Lactic Acid Production
Lactic acid was the first organic acid produced with microbes, carried out in 1880. In the twenty-first century, synthetic processes for the production of lactic acid (e.g., from lactonitrile) are competitive at the same costs as biological processes; lactic acid production is divided about equally between the two processes. 
The major supply of lactic acid in Europe is produced by fermentation using strains of L. bulgaricus when whey is used as the substrate, and other lactobacilli when different substrates are used.

According to the U.S. Food and Drug Administrating (FDA), lactic acid is a generally recognized as safe (GRAS) additive for miscellaneous or general purpose uses. 
It was one of the earliest organic acids used in foods. Lactic acid is used by the food industry in a number of ways: it is used in packing Spanish olives, where it inhibits spoilage and further fermentation; it aids in the stabilization of dried-egg powder; it improves the taste of certain pickles when added to vinegar; it is used to acidify the grape juice (must) in winemaking; in frozen confections, it imparts a milky tart taste and does not mask other natural flavors. 
Lactic acid is also used in the production of the emulsifiers calcium and sodium stearoyl lactylates, which function as dough conditioners. 
The sodium and potassium salts of lactic acid have significant antimicrobial properties, including in meat products against toxin production by Clostridium botulinum, and against Listeria monocytogenes in chicken, beef, and smoked salmon


Lactic acid is present in many foods both naturally and as a product of in situ fermentation, as in sauerkraut, yogurt, and many other fermented foods. 
Lactic acid is also a principal metabolic intermediate in most living organisms. 
Sodium and potassium lactates are produced commercially by neutralization of natural or synthetic lactic acid (FDA 184.1768, 1639). 
Lactic acid to be used as a food additive can be obtained either by fermentation of carbohydrates or by a chemical procedure involving formation of lactonitrile from acetaldehyde and hydrogen cyanide and subsequent hydrolysis (FDA 184.1061).

The microbiological and chemical procedures to obtain lactic acid are very competitive, with similar production costs. 
One method of biosynthesis in common use starts with glucose and produces pyruvate, which can be converted to both the l(+) and d(−) isomers using a stereospecific lactate dehydrogenase; however, only the l(+) form is produced commercially. 
The racemic mixture is always obtained by chemical synthesis. Synthetic lactic acid is free of the contaminants normally found in the product obtained by fermentation, and so it is completely colorless and probably more stable. 
Lactic acid and its salts are highly hygroscopic, and therefore are usually handled in concentrated solutions (60–80% by weight) rather than in solid form. 
These solutions are colorless and odorless, and have a mild saline taste

Lactic Acid
Lactic acid is an organic acid generated by microbial fermentation. Several studies have tested a 2% concentration of lactic acid as a sanitizer, either by itself or in combination with a surface-active agent. 
Lactic acid–based sanitizers interfere with cell membrane permeability and cell functions such as nutrient transport. 
These sanitizers are very promising and research is ongoing regarding their uses. 
For example, in a recent study, ten commercially available sanitizers were tested for their effectiveness against Listeria monocytogenes on high-density polyethylene cutting boards. 
Of all the products tested, which included QACs and sodium hypochlorite, a lactic-based sanitizer was the most effective against biofilm cells.

Lactic acid is used since 1990s as a fine chemical (production 60 000–80 000 tons yr−1). A major share (25 000 tons yr−1) is used as additive in the food industry. 
The second main application is as building block for green polymers, solvents, and plasticizers. 
Lactic acid is chemically produced by hydrocyanation (Figure 1) followed by hydrolysis of the cyanohydrin. 
The main drawbacks are the manipulation of hydrogen cyanide (HCN), the production of (NH4)2SO4 (1 eq), and the complex purification steps to obtain food-grade lactic acid because the racemic acid is obtained. 
To overcome these difficulties, the anaerobic fermentation from carbohydrates using Lactobacillus delbrueckii is a good alternative because only (S)-lactic acid is obtained in only one step. 
The fermentation is performed at 50 °C over 2–8 days with a yield of 85–95% and the product concentration is 100 g l−1. 
The isolation of (S)-lactic acid from biomass is easy using conventional methodologies

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