El ácido láctico es un ácido orgánico . Tiene una fórmula molecular CH 3 CH (OH) COOH. Es blanco en estado sólido y es miscible con agua. [2] Cuando está disuelto, forma una solución incolora. La producción incluye tanto síntesis artificial como fuentes naturales. El ácido láctico es un alfa-hidroxiácido (AHA) debido a la presencia de un grupo hidroxilo adyacente al grupo carboxilo . Se utiliza como intermedio sintético en muchas industrias de síntesis orgánica y en diversas industrias bioquímicas . La base conjugada del ácido láctico se llama lactato..
Nombres | |||
---|---|---|---|
Nombre IUPAC preferido Ácido 2-hidroxipropanoico [1] | |||
Otros nombres Ácido láctico [1] Ácido lácteo | |||
Identificadores | |||
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Modelo 3D ( JSmol ) | |||
3DMet | |||
1720251 | |||
CHEBI | |||
CHEMBL | |||
ChemSpider | |||
Tarjeta de información ECHA | 100.000.017 | ||
Número CE |
| ||
Número e | E270 (conservantes) | ||
362717 | |||
KEGG | |||
PubChem CID | |||
Número RTECS |
| ||
UNII |
| ||
un numero | 3265 | ||
Tablero CompTox ( EPA ) | |||
| |||
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Propiedades | |||
C 3 H 6 O 3 | |||
Masa molar | 90.078 g · mol −1 | ||
Punto de fusion | 18 ° C (64 ° F; 291 K) | ||
Punto de ebullición | 122 ° C (252 ° F; 395 K) a 15 mmHg | ||
Miscible [2] | |||
Acidez (p K a ) | 3,86, [3] 15,1 [4] | ||
Termoquímica | |||
Entalpía estándar de combustión (Δ c H ⦵ 298 ) | 1361,9 kJ / mol, 325,5 kcal / mol, 15,1 kJ / g, 3,61 kcal / g | ||
Farmacología | |||
Código ATC | G01AD01 ( OMS ) QP53AG02 ( OMS ) | ||
Peligros | |||
Pictogramas GHS | [5] | ||
Declaraciones de peligro GHS | H315 , H318 [5] | ||
Consejos de prudencia del SGA | P280 , P305 + 351 + 338 [5] | ||
Compuestos relacionados | |||
Otros aniones | Lactato | ||
Ácidos carboxílicos relacionados | Ácido acético Ácido glicólico Ácido propiónico Ácido 3-hidroxipropanoico Ácido malónico Ácido butírico Ácido hidroxibutírico | ||
Compuestos relacionados | 1-Propanol 2-Propanol propionaldehído acroleína sodio lactato lactato de etilo | ||
Salvo que se indique lo contrario, los datos se proporcionan para materiales en su estado estándar (a 25 ° C [77 ° F], 100 kPa). | |||
verificar ( ¿qué es ?) | |||
Referencias de Infobox | |||
En solución, puede ionizarse, produciendo el ion lactato CH
3CH (OH) CO-
2. Comparado con el ácido acético , su p K a es 1 unidad menos, lo que significa que el ácido láctico es diez veces más ácido que el ácido acético. Esta mayor acidez es la consecuencia del enlace de hidrógeno intramolecular entre el α-hidroxilo y el grupo carboxilato.
El ácido láctico es quiral y consta de dos enantiómeros . Uno se conoce como ácido L - (+) - láctico o ácido ( S ) -láctico y el otro, su imagen especular, es ácido D - (-) - láctico o ácido ( R ) -láctico. Una mezcla de los dos en cantidades iguales se llama ácido DL - láctico o ácido láctico racémico . El ácido láctico es higroscópico . El ácido DL- láctico es miscible con agua y con etanol por encima de su punto de fusión, que se sitúa en torno a los 16, 17 o 18 ° C. El ácido D- láctico y el ácido L- láctico tienen un punto de fusión más alto. El ácido láctico producido por la fermentación de la leche es a menudo racémico, aunque ciertas especies de bacterias producen únicamente ácido ( R ) -láctico. Por otro lado, el ácido láctico producido por la respiración anaeróbica en los músculos de los animales tiene la configuración ( S ) y a veces se le llama ácido "sarcoáctico", del griego "sarx" para carne.
En los animales, el L- lactato se produce constantemente a partir del piruvato a través de la enzima lactato deshidrogenasa (LDH) en un proceso de fermentación durante el metabolismo normal y el ejercicio . [6] No aumenta en concentración hasta que la tasa de producción de lactato excede la tasa de eliminación de lactato, que se rige por varios factores, incluidos los transportadores de monocarboxilato , la concentración e isoforma de LDH y la capacidad oxidativa de los tejidos. [7] La concentración de lactato en sangre suele ser de 1 a 2 mM en reposo, pero puede aumentar a más de 20 mM durante un esfuerzo intenso y hasta 25 mM después. [8] [9] Además de otras funciones biológicas, L ácido láctico es el principal endógeno agonista de receptor de ácido hidroxicarboxílico 1 (HCA 1 ), que es un G i / o -junto G receptor acoplado a la proteína (GPCR). [10] [11]
En la industria, la fermentación del ácido láctico la realizan las bacterias del ácido láctico , que convierten los carbohidratos simples como la glucosa , la sacarosa o la galactosa en ácido láctico. Estas bacterias también pueden crecer en la boca ; el ácido que producen es responsable de la caries dental conocida como caries . [12] [13] [14] [15] En la medicina , lactato es uno de los principales componentes de la solución de lactato de Ringer y solución de Hartmann . Estos fluidos intravenosos consisten en cationes de sodio y potasio junto con aniones de lactato y cloruro en solución con agua destilada , generalmente en concentraciones isotónicas con la sangre humana . Se utiliza con mayor frecuencia para la reanimación con líquidos después de una pérdida de sangre debido a un traumatismo , una cirugía o quemaduras .
Historia
El químico sueco Carl Wilhelm Scheele fue la primera persona en aislar el ácido láctico en 1780 de la leche agria . [16] El nombre refleja la forma de combinación de lactosa derivada de la palabra latina lac , que significa leche. En 1808, Jöns Jacob Berzelius descubrió que el ácido láctico (en realidad L- lactato) también se produce en los músculos durante el esfuerzo. [17] Su estructura fue establecida por Johannes Wislicenus en 1873.
En 1856, Louis Pasteur descubrió el papel de Lactobacillus en la síntesis de ácido láctico . Esta vía fue utilizada comercialmente por la farmacia alemana Boehringer Ingelheim en 1895.
En 2006, la producción mundial de ácido láctico alcanzó las 275.000 toneladas con un crecimiento anual medio del 10%. [18]
Producción
El ácido láctico se produce industrialmente por fermentación bacteriana de carbohidratos o por síntesis química a partir de acetaldehído . [19] En 2009, el ácido láctico se produjo predominantemente (70-90%) [20] por fermentación. La producción de ácido láctico racémico que consiste en una mezcla 1: 1 de estereoisómeros D y L , o de mezclas con hasta un 99,9% de ácido L- láctico, es posible mediante fermentación microbiana. La producción a escala industrial de ácido D- láctico por fermentación es posible, pero mucho más desafiante.
Producción fermentativa
Los productos lácteos fermentados se obtienen industrialmente mediante fermentación de la leche o suero de leche por Lactobacillus bacterias: Lactobacillus acidophilus , Lactobacillus casei , Lactobacillus delbrueckii subsp. bulgaricus ( Lactobacillus bulgaricus ), Lactobacillus helveticus , Lactococcus lactis y Streptococcus salivarius subsp. thermophilus ( Streptococcus thermophilus ).
Como material de partida para la producción industrial de ácido láctico, se puede utilizar casi cualquier fuente de carbohidratos que contenga azúcares C 5 y C 6 . Con frecuencia se utilizan sacarosa pura, glucosa de almidón, azúcar sin refinar y jugo de remolacha. [21] Las bacterias productoras de ácido láctico se pueden dividir en dos clases: bacterias homofermentativas como Lactobacillus casei y Lactococcus lactis , que producen dos moles de lactato a partir de un mol de glucosa, y especies heterofermentativas que producen un mol de lactato a partir de un mol de glucosa, así como dióxido de carbono y ácido acético / etanol . [22]
Produccion quimica
El ácido láctico racémico se sintetiza industrialmente haciendo reaccionar acetaldehído con cianuro de hidrógeno e hidrolizando el lactonitrilo resultante . Cuando la hidrólisis se realiza con ácido clorhídrico , se forma cloruro de amonio como subproducto; La empresa japonesa Musashino es uno de los últimos grandes fabricantes de ácido láctico por esta vía. [23] La síntesis de ácidos lácticos racémicos y enantiopuros también es posible a partir de otros materiales de partida ( acetato de vinilo , glicerol , etc.) mediante la aplicación de procedimientos catalíticos. [24]
Biología
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 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+.[26] 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 CH 3COCO− 2 + 2 H+ + 2 NADH + 2 ATP4− + 2 H2O | |
Subsequent lactate− production absorbs these protons: | |||
2 CH 3COCO− 2 + 2 H+ + 2 NADH | → | 2 CH 3CH(OH)CO− 2 + 2 NAD+ | |
Overall: | |||
C6H12O6 + 2 NAD+ + 2 ADP3− + 2 HPO2− 4 | → | 2 CH 3COCO− 2 + 2 H+ + 2 NADH + 2 ATP4− + 2 H2O | |
→ | 2 CH 3CH(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
- C 6H 12O 6 → 2 CH
3COCO−
2 + 2 H +
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 predominately 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]
Análisis de sangre
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.
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.
Precursor de polímero
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.
Aplicaciones farmacéuticas y cosméticas
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.
Alimentos
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.[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.[41] The energy density of lactic acid is 362 kilocalories (1,510 kJ) per 100 g.[42]
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.[43][44]
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.[45]
As a food additive it is approved for use in the EU,[46] USA[47] and Australia and New Zealand;[48] 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.[49] It is an ingredient in processed foods and is used as a decontaminant during meat processing.[50] Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis.[49] Carbohydrate sources include corn, beets, and cane sugar.[51]
Falsificación
Lactic acid has historically been used to assist with the erasure of inks from official papers to be modified during forgery.[52]
Productos de limpieza
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.
Ver también
- Hydroxybutyric acid
- Acids in wine
- Alanine cycle
- Biodegradable plastic
- Dental caries
- MCT1, a lactate transporter
- Thiolactic acid
Referencias
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- ^ a b c d Derived from mass values using molar mass of 90.08 g/mol
- ^ "USDA National Nutrient Database for Standard Reference, Release 28 (2015) Documentation and User Guide" (PDF). 2015. p. 13.
- ^ 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.
- ^ Greenfield H, Southgate D (2003). Food Composition Data: Production, Management and Use. Rome: FAO. p. 146. ISBN 9789251049495.
- ^ "Brewing With Lactic Acid Bacteria". MoreBeer.
- ^ Lambic (Classic Beer Style) – Jean Guinard
- ^ Li Li, Xiaohong Yao, Caihong Zhong and Xuzhong Chen (January 2010). "Akebia: A Potential New Fruit Crop in China". HortScience. 45 (1): 4–10. doi:10.21273/HORTSCI.45.1.4.CS1 maint: multiple names: authors list (link)
- ^ "Current EU approved additives and their E Numbers". UK Food Standards Agency. Retrieved 27 October 2011.
- ^ "Listing of Food Additives Status Part II". US Food and Drug Administration. Retrieved 27 October 2011.
- ^ "Standard 1.2.4 – Labelling of ingredients". Australia New Zealand Food Standards Code. Retrieved 27 October 2011.
- ^ a b "Listing of Specific Substances Affirmed as GRAS:Lactic Acid". US FDA. Retrieved 20 May 2013.
- ^ "Purac Carcass Applications". Purac. Retrieved 20 May 2013.
- ^ "Agency Response Letter GRAS Notice No. GRN 000240". FDA. US FDA. Retrieved 20 May 2013.
- ^ Druckerman P (2 October 2016). "If I Sleep for an Hour, 30 People Will Die". The New York Times.
enlaces externos
- Corn Plastic to the Rescue
- Lactic Acid: Information and Resources
- Lactic Acid Is Not Muscles' Foe, It's Fuel
- Fitzgerald M (26 January 2010). "The Lactic Acid Myths". Competitor Running.