Lactic acid

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L-lactate
)

Lactic acid
Names
Preferred IUPAC name
2-Hydroxypropanoic acid[1]
Other names
  • Lactic acid[1]
  • Milk acid
Identifiers
3D model (
JSmol
)
3DMet
1720251
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard
 100.000.017 Edit this at Wikidata
EC Number
  • 200-018-0
E number E270 (preservatives)
362717
IUPHAR/BPS
KEGG
RTECS number
  • OD2800000
UNII
UN number 3265
  • InChI=1S/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)/t2-/m0/s1 checkY
    Key: JVTAAEKCZFNVCJ-REOHCLBHSA-N checkY
  • CC(O)C(=O)O
Properties
C3H6O3
Molar mass 90.078 g·mol−1
Melting point 18 °C (64 °F; 291 K)
Boiling point 122 °C (252 °F; 395 K) at 15 mmHg
Miscible[2]
Acidity (pKa) 3.86,[3] 15.1[4]
Thermochemistry
Std enthalpy of
combustion
(ΔcH⦵298)
 1361.9 kJ/mol, 325.5 kcal/mol, 15.1 kJ/g, 3.61 kcal/g
Related compounds
Other anions
 Lactate
Related compounds
Pharmacology
QP53AG02 (WHO
)
Hazards
GHS labelling:
GHS05: Corrosive[5]
H315, H318[5]
P280, P305+P351+P338[5]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Lactic acid is an

conjugate base of lactic acid is called lactate (or the lactate anion). The name of the derived acyl group
is lactoyl.

In solution, it can ionize by a loss of a proton to produce the lactate ion CH
3CH(OH)CO−
2. Compared to acetic acid, its pKa is 1 unit less, meaning lactic acid is ten times more acidic than acetic acid.[6] This higher acidity is the consequence of the intramolecular hydrogen bonding between the α-hydroxyl and the carboxylate group.

Lactic acid is

miscible with water and with ethanol above its melting point, which is about 16 to 18 °C (61 to 64 °F). 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 D-lactic acid.[7]
On the other hand, lactic acid produced by anaerobic respiration in animal muscles has the (L) enantiomer and is sometimes called "sarcolactic" acid, from the Greek sarx, meaning "flesh".

In animals, L-lactate is constantly produced from

endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA1), which is a Gi/o-coupled G protein-coupled receptor (GPCR).[11][12]

In industry,

burns
.

History

Swedish chemist Carl Wilhelm Scheele was the first person to isolate lactic acid in 1780 from sour milk.[17] The name reflects the lact- combining form derived from the Latin word lac, meaning "milk". In 1808, Jöns Jacob Berzelius discovered that lactic acid (actually L-lactate) also is produced in muscles during exertion.[18] 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%.[19]

Production

Lactic acid is produced industrially by bacterial fermentation of carbohydrates, or by chemical synthesis from acetaldehyde.[20] As of 2009, lactic acid was produced predominantly (70–90%)[21] 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

Streptococcus salivarius subsp. thermophilus
(Streptococcus thermophilus).

As a starting material for industrial production of lactic acid, almost any carbohydrate source containing C
5 (Pentose sugar) and C
6 (Hexose sugar) can be used. Pure sucrose, glucose from starch, raw sugar, and beet juice are frequently used.[22] 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.[23]

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.[24] Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials (vinyl acetate, glycerol, etc.) by application of catalytic procedures.[25]

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).[11][12]

Exercise and lactate

See also:
N-Lactoylphenylalanine

During power exercises such as

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:

However, lactate is continually formed at rest and during all exercise intensities. Lactate serves as a metabolic fuel being produced and oxidatively disposed in resting and exercising muscle. Some causes of this are metabolism in

lack mitochondria, and limitations resulting from the enzyme activity that occurs in muscle fibers having high glycolytic capacity.[26] Lactic acidosis is a physiological condition characterized by accumulation of lactate (especially L-lactate), with formation of an excessively low pH in the tissues – a form of metabolic acidosis
.

Lactic acidosis during exercise may occur due to the H+ from ATP hydrolysis (ATP4− + H2O → ADP3− + HPO2−4 + H+), and that reducing pyruvate to lactate (pyruvate− + NADH + H+ → lactate− + NAD+) actually consumes H+.[27] The causative factors of the increase in [H+] result from the production of lactate− from a neutral molecule, increasing [H+] to maintain electroneutrality.[28] A contrary view is 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+

The combined effect is:

C6H12O6 + 2 ADP3− + 2HPO2−4 → 2 CH3CH(OH)CO−2 + 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 CH3CH(OH)CO−2 + 2 H+

Neural tissue energy source

Although

lactate-shuttle hypothesis, glial cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons.[31][32] Because of this local metabolic activity of glial cells, the extracellular fluid immediately surrounding neurons strongly differs in composition from the blood or cerebrospinal fluid, being much richer with lactate, as was found in microdialysis studies.[29]

Brain development metabolism

Some evidence suggests that lactate is important at early stages of development for brain metabolism in

inhibitory than it was previously assumed,[33] acting either through better support of metabolites,[29] or alterations in base intracellular pH levels,[34][35] or both.[36]

Studies of brain slices of mice show that

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

Lactate can also serve as an important source of energy for other organs, including the heart and liver. During physical activity, up to 60% of the heart muscle's energy turnover rate derives from lactate oxidation.[17]

Blood testing

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

arterial (even if it is more difficult than venipuncture
), because lactate levels differ substantially between arterial and venous, and the arterial level is more representative for this purpose.

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

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

Uses

Polymer precursor

Main article: polylactic acid

Two molecules of lactic acid can be dehydrated to the

biodegradable polyesters. PLA is an example of a plastic that is not derived from petrochemicals
.

Pharmaceutical and cosmetic applications

Lactic acid is also employed in

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

Lactic acid containing bacteria have shown promise in reducing

oxaluria with its descaling properties on calcium compounds.[41]

Foods

Fermented food

Lactic acid is found primarily in sour milk products, such as kumis, 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.[42] 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.[43] The energy density of lactic acid is 362 kilocalories (1,510 kJ) per 100 g.[44]

Some beers (

Flanders red and American wild ale.[45][46]

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.[47]

Separately added

As a

INS number 270 or as E number E270. Lactic acid is used as a food preservative, curing agent, and flavoring agent.[51] It is an ingredient in processed foods and is used as a decontaminant during meat processing.[52] Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis.[51] Carbohydrate sources include corn, beets, and cane sugar.[53]

Forgery

Lactic acid has historically been used to assist with the erasure of inks from official papers to be modified during forgery.[54]

Cleaning products

Lactic acid is used in some liquid cleaners as a descaling agent for removing hard water deposits such as calcium carbonate.[55]

See also

References

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    ISBN 978-0-85404-182-4
    .
  2. ^ a b Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. ^ Dawson RM, et al. (1959). Data for Biochemical Research. Oxford: Clarendon Press.
  4. S2CID 11615864
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  5. ^ a b c Sigma-Aldrich Co., DL-Lactic acid.
  6. ^ "rac-lactic acid (CHEBI:28358)". www.ebi.ac.uk. Retrieved 8 March 2024.
  7. ^ "(S)-lactic acid (CHEBI:422)". www.ebi.ac.uk. Retrieved 5 January 2024.
  8. ^
    PMID 23650363
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  9. ^ "Lactate Profile". UC Davis Health System, Sports Medicine and Sports Performance. Retrieved 23 November 2015.
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  11. ^
    PMID 21454438
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  12. ^ a b Offermanns S, Colletti SL, IJzerman AP, Lovenberg TW, Semple G, Wise A, Waters MG. "Hydroxycarboxylic acid receptors". IUPHAR/BPS Guide to Pharmacology. International Union of Basic and Clinical Pharmacology. Retrieved 13 July 2018.
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  17. ^
    doi:10.1146/annurev-cancerbio-030419-033556
    .
  18. ^ Roth SM. "Why does lactic acid build up in muscles? And why does it cause soreness?". Scientific American. Retrieved 23 January 2006.
  19. ^ "NNFCC Renewable Chemicals Factsheet: Lactic Acid". NNFCC.
  20. ISBN 0792306252
    , 9780792306252
  21. ISBN 978-3-446-41683-3
    .
  22. ISBN 978-0-470-29366-9
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  27. S2CID 2745168
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  39. ^ a b c d Blood Test Results – Normal Ranges Archived 2 November 2012 at the Wayback Machine Bloodbook.Com
  40. ^ a b c d Derived from mass values using molar mass of 90.08 g/mol
  41. PMID 11532105
    .
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  43. ^ For example, in this USDA database entry for yoghurt the food energy is calculated using given coefficients for carbohydrate, fat, and protein. (One must click on "Full report" to see the coefficients.) The calculated value is based on 4.66 grams of carbohydrate, which is exactly equal to the sugars.
  44. ISBN 9789251049495
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  45. ^ "Brewing With Lactic Acid Bacteria". MoreBeer.
  46. ^ Lambic (Classic Beer Style) – Jean Guinard
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  49. ^ "Listing of Food Additives Status Part II". US Food and Drug Administration. Retrieved 27 October 2011.
  50. ^ "Standard 1.2.4 – Labelling of ingredients". Australia New Zealand Food Standards Code. Retrieved 27 October 2011.
  51. ^ a b "Listing of Specific Substances Affirmed as GRAS:Lactic Acid". US FDA. Retrieved 20 May 2013.
  52. ^ "Purac Carcass Applications". Purac. Archived from the original on 29 July 2013. Retrieved 20 May 2013.
  53. ^ "Agency Response Letter GRAS Notice No. GRN 000240". FDA. US FDA. Retrieved 20 May 2013.
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  55. ^ Naushad, Mu.; Lichtfouse, Eric (2019). Sustainable Agriculture Reviews 34: Date Palm for Food Medicine and the Environment. Springer. p. 162.

External links

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