Chemistry:Lactic acid

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Short description: Group of stereoisomers
Lactic acid
7 Milchsäure.svg
Lactic-acid-from-xtal-3D-bs-17.png
Names
Preferred IUPAC name
2-Hydroxypropanoic acid[1]
Other names
  • Lactic acid[1]
  • Milk acid
Identifiers
3D model (JSmol)
3DMet
1720251
ChEBI
ChEMBL
ChemSpider
EC Number
  • 200-018-0
362717
KEGG
RTECS number
  • OD2800000
UNII
UN number 3265
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
1361.9 kJ/mol, 325.5 kcal/mol, 15.1 kJ/g, 3.61 kcal/g
Related compounds
Other anions
 Lactate
Related compounds
Pharmacology
1=ATC code }} G01AD01 (WHO) QP53AG02 (WHO)
Hazards
GHS pictograms GHS05: Corrosive[5]
H315, H318[5]
P280, P305+351+338[5]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Tracking categories (test):

Lactic acid is an organic acid. It has the molecular formula CH
3CH(OH)COOH. It is white in the solid state and it is miscible with water.[2] When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natural sources. Lactic acid is an alpha-hydroxy acid (AHA) due to the presence of a hydroxyl group adjacent to the carboxyl group. It is used as a synthetic intermediate in many organic synthesis industries and in various biochemical industries. The conjugate base of lactic acid is called lactate (or the lactate anion). The name of the derived acyl group is lactoyl.

In solution, it can ionize by a loss of a proton to produce the lactate ion 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, (S)-lactic acid, or (+)-lactic acid, and the other, its mirror image, is D-lactic acid, (R)-lactic acid, or (−)-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 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.[6] 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 pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise.[7] 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.[7] 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.[8][9] 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.[12][13][14][15] 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.[16] 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.[17] 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%.[18]

Production

Lactic acid is produced industrially by bacterial fermentation of carbohydrates, or by chemical synthesis from acetaldehyde.[19] (As of 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, Lacticaseibacillus casei (Lactobacillus casei), Lactobacillus delbrueckii subsp. bulgaricus (Lactobacillus bulgaricus), Lactobacillus helveticus, Lactococcus lactis , Bacillus amyloliquefaciens, and Streptococcus salivarius subsp. thermophilus (Streptococcus thermophilus).

As a starting material for industrial production of lactic acid, almost any carbohydrate source containing C5 (Pentose sugar) and C6 (Hexose sugar) can be used. Pure sucrose, glucose from starch, raw sugar, and beet juice are frequently used.[21] Lactic acid producing bacteria can be divided in two classes: homofermentative bacteria like Lactobacillus casei and Lactococcus lactis, producing two moles of lactate from one mole of glucose, and heterofermentative species producing one mole of lactate from one mole of glucose as well as carbon dioxide and acetic acid/ethanol.[22]

Chemical production

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

Biology

Molecular biology

L-Lactic acid is the primary endogenous agonist of hydroxycarboxylic acid receptor 1 (HCA1), a Gi/o-coupled G protein-coupled receptor (GPCR).[10][11]

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[25]
    • If blood glucose concentrations are high, the glucose can be used to build up the liver's glycogen stores.

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 red blood cells that lack mitochondria, and limitations resulting from the enzyme activity that occurs in muscle fibers having high glycolytic capacity.[25] 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+.[26] The causative factors of the increase in [H+] result from the production of lactate− from a neutral molecule, increasing [H+] to maintain electroneutrality.[27] 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+:

[math]\ce{ C6H12O6 + 2NAD+ + 2ADP^3- + 2HPO4^2- -> 2CH3COCO2- + 2H+ + 2NADH + 2ATP^4- + 2H2O }[/math]

Subsequent lactate− production absorbs these protons:

[math]\ce{ 2CH3COCO2- + 2H+ + 2NADH -> 2CH3CH(OH)CO2- + 2NAD+ }[/math]

Overall:

[math]\ce{ C6H12O6 + 2NAD+ + 2ADP^3- + 2HPO4^2- -> 2CH3COCO2- + 2H+ + 2NADH + 2ATP^4- + 2H2O }[/math]

[math]\ce{ -> 2CH3CH(OH)CO2- + 2NAD+ + 2ATP^4- + 2H2O }[/math]

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

[math]\ce{ C6H12O6 -> 2CH3COCO2- + 2H+ }[/math]

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

Neural tissue energy source

Although glucose is usually assumed to be the main energy source for living tissues, there are a few reports that indicate that it is lactate, and not glucose, that is preferentially metabolized by neurons in the brain of several mammalian species (the notable ones being mice, rats, and humans).[28][29][non-primary source needed] According to the lactate-shuttle hypothesis, glial cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons.[30][31] 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.[28]

Brain development metabolism

Some evidence suggests that lactate is important at early stages of development for brain metabolism in prenatal and early postnatal subjects, with lactate at these stages having higher concentrations in body liquids, and being utilized by the brain preferentially over glucose.[28] 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,[32] acting either through better support of metabolites,[28] or alterations in base intracellular pH levels,[33][34] or both.[35]

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.[36] 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."[37]

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.

Uses

Polymer precursor

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

Pharmaceutical and cosmetic applications

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

Lactic acid containing bacteria have shown promise in reducing oxaluria with its descaling properties on calcium compounds.[40]

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.[41] 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.[42] The energy density of lactic acid is 362 kilocalories (1,510 kJ) per 100 g.[43]

Some beers (sour beer) purposely contain lactic acid, one such type being Belgian lambics. Most commonly, this is produced naturally by various strains of bacteria. These bacteria ferment sugars into acids, unlike the yeast that ferment sugar into ethanol. After cooling the wort, yeast and bacteria are allowed to "fall" into the open fermenters. Brewers of more common beer styles would ensure that no such bacteria are allowed to enter the fermenter. Other sour styles of beer include Berliner weisse, Flanders red and American wild ale.[44][45]

In winemaking, a bacterial process, natural or controlled, is often used to convert the naturally present malic acid to lactic acid, to reduce the sharpness and for other flavor-related reasons. This malolactic fermentation is undertaken by lactic acid bacteria.

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.[46]

Separately added

As a food additive it is approved for use in the EU,[47] United States[48] and Australia and New Zealand;[49] 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.[50] It is an ingredient in processed foods and is used as a decontaminant during meat processing.[51] Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis.[50] Carbohydrate sources include corn, beets, and cane sugar.[52]

Forgery

Lactic acid has historically been used to assist with the erasure of inks from official papers to be modified during forgery.[53]

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 is used in some antibacterial soaps and dish detergents as a replacement for triclosan.

See also

References

  1. ↑ 1.0 1.1 "CHAPTER P-6. Applications to Specific Classes of Compounds". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 748. doi:10.1039/9781849733069-00648. ISBN 978-0-85404-182-4. 
  2. ↑ 2.0 2.1 Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  3. ↑ Data for Biochemical Research. Oxford: Clarendon Press. 1959. 
  4. ↑ "Determination of the pKa value of the hydroxyl group in the alpha-hydroxycarboxylates citrate, malate and lactate by 13C NMR: implications for metal coordination in biological systems". Biometals 22 (5): 771–8. October 2009. doi:10.1007/s10534-009-9224-5. PMID 19288211. 
  5. ↑ 5.0 5.1 5.2 Sigma-Aldrich Co., DL-Lactic acid.
  6. ↑ "(S)-lactic acid (CHEBI:422)". https://www.ebi.ac.uk/chebi/searchId.do?printerFriendlyView=true&locale=null&chebiId=422&viewTermLineage=null&structureView=&. 
  7. ↑ 7.0 7.1 "Skeletal muscle PGC-1α controls whole-body lactate homeostasis through estrogen-related receptor α-dependent activation of LDH B and repression of LDH A". Proceedings of the National Academy of Sciences of the United States of America 110 (21): 8738–43. May 2013. doi:10.1073/pnas.1212976110. PMID 23650363. Bibcode: 2013PNAS..110.8738S. 
  8. ↑ "Lactate Profile". UC Davis Health System, Sports Medicine and Sports Performance. http://www.ucdmc.ucdavis.edu/sportsmedicine/resources/lactate_description.html. 
  9. ↑ "Blood lactate measurements and analysis during exercise: a guide for clinicians". Journal of Diabetes Science and Technology 1 (4): 558–69. July 2007. doi:10.1177/193229680700100414. PMID 19885119. 
  10. ↑ 10.0 10.1 "International Union of Basic and Clinical Pharmacology. LXXXII: Nomenclature and Classification of Hydroxy-carboxylic Acid Receptors (GPR81, GPR109A, and GPR109B)". Pharmacological Reviews 63 (2): 269–90. June 2011. doi:10.1124/pr.110.003301. PMID 21454438. 
  11. ↑ 11.0 11.1 "Hydroxycarboxylic acid receptors". International Union of Basic and Clinical Pharmacology. http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=48. 
  12. ↑ "Ecology of lactobacilli in the oral cavity: a review of literature". The Open Microbiology Journal 2: 38–48. 2008. doi:10.2174/1874285800802010038. PMID 19088910. 
  13. ↑ "Correlations of oral bacterial arginine and urea catabolism with caries experience". Oral Microbiology and Immunology 24 (2): 89–95. April 2009. doi:10.1111/j.1399-302X.2008.00477.x. PMID 19239634. 
  14. ↑ "Bacteria of dental caries in primary and permanent teeth in children and young adults". Journal of Clinical Microbiology 46 (4): 1407–17. April 2008. doi:10.1128/JCM.01410-07. PMID 18216213. 
  15. ↑ "Diversity of lactobacilli in the oral cavities of young women with dental caries". Caries Research 41 (1): 2–8. 2007. doi:10.1159/000096099. PMID 17167253. 
  16. ↑ 16.0 16.1 Parks, Scott K.; Mueller-Klieser, Wolfgang; Pouysségur, Jacques (2020). "Lactate and Acidity in the Cancer Microenvironment". Annual Review of Cancer Biology 4: 141–158. doi:10.1146/annurev-cancerbio-030419-033556. 
  17. ↑ Roth, Stephen M.. "Why does lactic acid build up in muscles? And why does it cause soreness?". https://www.scientificamerican.com/article/why-does-lactic-acid-buil/. 
  18. ↑ "NNFCC Renewable Chemicals Factsheet: Lactic Acid". NNFCC. http://www.nnfcc.co.uk/publications/nnfcc-renewable-chemicals-factsheet-lactic-acid. 
  19. ↑ H. Benninga (1990): "A History of Lactic Acid Making: A Chapter in the History of Biotechnology". Volume 11 of Chemists and Chemistry. Springer, ISBN:0792306252, 9780792306252
  20. ↑ Endres, Hans-Josef (2009). Technische Biopolymere. München: Hanser-Verlag. pp. 103. ISBN 978-3-446-41683-3. 
  21. ↑ Groot, Wim; van Krieken, Jan; Slekersl, Olav; de Vos, Sicco (2010-10-19). "Chemistry and production of lactic acid, lactide and poly(lactic acid)". in Auras, Rafael; Lim, Long-Tak; Selke, Susan E. M. et al.. Poly(Lactic acid). Hoboken: Wiley. p. 3. ISBN 978-0-470-29366-9. 
  22. ↑ König, Helmut; Fröhlich, Jürgen (2009). Lactic acid bacteria in Biology of Microorganisms on Grapes, in Must and in Wine. Springer-Verlag. p. 3. ISBN 978-3-540-85462-3. 
  23. ↑ Westhoff, Gerrit; Starr, John N. (2012). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_097.pub3. 
  24. ↑ Shuklov, Ivan A.; Dubrovina, Natalia V.; Kühlein, Klaus; Börner, Armin (2016). "Chemo-Catalyzed Pathways to Lactic Acid and Lactates". Advanced Synthesis and Catalysis 358 (24): 3910–3931. doi:10.1002/adsc.201600768. 
  25. ↑ 25.0 25.1 Exercise Physiology: Energy, Nutrition, and Human Performance. Wolters Kluwer/Lippincott Williams & Wilkins Health. 2010. ISBN 978-0-683-05731-7. https://archive.org/details/exercisephysiolo00mcar_0. 
  26. ↑ "Biochemistry of exercise-induced metabolic acidosis". American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 287 (3): R502–R516. September 2004. doi:10.1152/ajpregu.00114.2004. PMID 15308499. 
  27. ↑ "Applying physicochemical principles to skeletal muscle acid-base status". American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 289 (3): R891–4; author reply R904–910. September 2005. doi:10.1152/ajpregu.00225.2005. PMID 16105823. 
  28. ↑ 28.0 28.1 28.2 28.3 "Neuronal activity in vitro and the in vivo reality: the role of energy homeostasis". Trends in Pharmacological Sciences 31 (9): 394–401. September 2010. doi:10.1016/j.tips.2010.06.005. PMID 20633934. 
  29. ↑ "In vivo evidence for lactate as a neuronal energy source". The Journal of Neuroscience 31 (20): 7477–85. May 2011. doi:10.1523/JNEUROSCI.0415-11.2011. PMID 21593331. PMC 6622597. http://www.zora.uzh.ch/55080/1/Wyss_Weber_J_Neuroscience%282011%29.pdf. 
  30. ↑ "Lactate metabolism: a new paradigm for the third millennium". The Journal of Physiology 558 (Pt 1): 5–30. July 2004. doi:10.1113/jphysiol.2003.058701. PMID 15131240. 
  31. ↑ "Activity-dependent regulation of energy metabolism by astrocytes: an update". Glia 55 (12): 1251–62. September 2007. doi:10.1002/glia.20528. PMID 17659524. 
  32. ↑ "Energy substrate availability as a determinant of neuronal resting potential, GABA signaling and spontaneous network activity in the neonatal cortex in vitro". Journal of Neurochemistry 112 (4): 900–12. February 2010. doi:10.1111/j.1471-4159.2009.06506.x. PMID 19943846. 
  33. ↑ "Depolarizing actions of GABA in immature neurons depend neither on ketone bodies nor on pyruvate". The Journal of Neuroscience 31 (1): 34–45. January 2011. doi:10.1523/JNEUROSCI.3314-10.2011. PMID 21209187. 
  34. ↑ "Spontaneous network events driven by depolarizing GABA action in neonatal hippocampal slices are not attributable to deficient mitochondrial energy metabolism". The Journal of Neuroscience 30 (46): 15638–42. November 2010. doi:10.1523/JNEUROSCI.3355-10.2010. PMID 21084619. 
  35. ↑ "Questioning the depolarizing effects of GABA during early brain development". Journal of Neurophysiology 106 (3): 1065–7. September 2011. doi:10.1152/jn.00293.2011. PMID 21593390. 
  36. ↑ "Lactate Effectively Covers Energy Demands during Neuronal Network Activity in Neonatal Hippocampal Slices". Frontiers in Neuroenergetics 3: 2. 2011. doi:10.3389/fnene.2011.00002. PMID 21602909. 
  37. ↑ "Lactate fuels the neonatal brain". Frontiers in Neuroenergetics 3: 4. 2011. doi:10.3389/fnene.2011.00004. PMID 21687795. 
  38. ↑ 38.0 38.1 38.2 38.3 Blood Test Results – Normal Ranges Bloodbook.Com
  39. ↑ 39.0 39.1 39.2 39.3 Derived from mass values using molar mass of 90.08 g/mol
  40. ↑ Campieri, C.; Campieri, M.; Bertuzzi, V.; Swennen, E.; Matteuzzi, D.; Stefoni, S.; Pirovano, F.; Centi, C. et al. (September 2001). "Reduction of oxaluria after an oral course of lactic acid bacteria at high concentration". Kidney International 60 (3): 1097–1105. doi:10.1046/j.1523-1755.2001.0600031097.x. ISSN 0085-2538. PMID 11532105. 
  41. ↑ "USDA National Nutrient Database for Standard Reference, Release 28 (2015) Documentation and User Guide". 2015. p. 13. http://www.ars.usda.gov/sp2UserFiles/Place/80400525/Data/SR/SR28/sr28_doc.pdf. 
  42. ↑ 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.
  43. ↑ Greenfield, Heather; Southgate, D.A.T. (2003). Food Composition Data: Production, Management and Use. Rome: FAO. p. 146. ISBN 9789251049495. 
  44. ↑ "Brewing With Lactic Acid Bacteria". https://www.morebeer.com/articles/brewing_with_lactic_acid_bacteria. 
  45. ↑ Lambic (Classic Beer Style) – Jean Guinard
  46. ↑ Li, Li; Yao, Xiaohong; Zhong, Caihong; Chen, Xuzhong (January 2010). "Akebia: A Potential New Fruit Crop in China". HortScience 45 (1): 4–10. doi:10.21273/HORTSCI.45.1.4. 
  47. ↑ "Current EU approved additives and their E Numbers". UK Food Standards Agency. http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist. 
  48. ↑ "Listing of Food Additives Status Part II". US Food and Drug Administration. https://www.fda.gov/Food/FoodIngredientsPackaging/FoodAdditives/ucm191033.htm#ftnT. 
  49. ↑ "Standard 1.2.4 – Labelling of ingredients". Australia New Zealand Food Standards Code. http://www.comlaw.gov.au/Details/F2011C00827. 
  50. ↑ 50.0 50.1 "Listing of Specific Substances Affirmed as GRAS:Lactic Acid". US FDA. http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=184.1061. 
  51. ↑ "Purac Carcass Applications". Purac. http://www.purac.com/EN/Food/Markets/Meat_poultry_and_fish/Applications/Carcass.aspx. 
  52. ↑ "Agency Response Letter GRAS Notice No. GRN 000240". FDA. US FDA. https://www.fda.gov/Food/IngredientsPackagingLabeling/GRAS/NoticeInventory/ucm153929.htm. 
  53. ↑ Druckerman, Pamela (2 October 2016). "If I Sleep for an Hour, 30 People Will Die". The New York Times. https://www.nytimes.com/2016/10/02/opinion/sunday/if-i-sleep-for-an-hour-30-people-will-die.html. 

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