Lactic acid
- 2- hydroxy propanoic acid
- 2 -hydroxypropionic acid
- (R) -lactic acid
- (S)- lactic acid
- ( RS)- lactic acid
- DL-lactic acid
- (±)- lactic acid
- E 270
- 50-21-5
- 10326-41-7 ( D-lactic acid)
- 79-33-4 (L- lactic acid )
- 598-82-3 (racemate )
G01AD01
Colorless, almost odorless, oily liquid (racemate )
Liquid (racemate ) fixed ( D-lactic acid)
1.21 g · cm -3 ( racemate)
122 ° C (20 hPa) (racemate )
10 Pa ( 25 ° C)
3.90 ( 25 ° C)
- Completely miscible with water
- Soluble in ethanol
1.4392 (20 ° C; racemate)
Risk
3,543 mg · kg -1 ( LD50, rat, oral)
Template: Infobox chemical / molecular formula search available
Lactic acid ( Acidum lacticum lat ) is a hydroxycarboxylic acid, that is an alkanoic acid having both a carboxyl group and a hydroxyl group. It is therefore also known as 2- hydroxypropionic acid, in accordance with the nomenclature of IUPAC recommendations, however, the term 2- hydroxypropanoic acid to be used. The salts and esters of lactic acid hot lactates.
(-) Due to their different optical activity of the D- is - lactic acid ( Syn: (R) -lactic acid ) as a left-turning lactic acid and L-( )- lactic acid ( Syn: (S) -lactic acid ) as a right-handed lactic acid respectively. Racemic lactic acid is a 1:1 - mixture of (R) - and (S) -lactic acid.
L-lactic acid
Lactic acid is in the form of lactate is an important intermediate product in the metabolism of, for example, as the degradation product of sugars by lactic acid fermentation. About 250,000 tons of lactic acid are produced annually worldwide, mainly in the food industry and for the production of polylactides (PLA; Also: polylactic acids ) can be used.
- 5.1 Nutrition, food and beverage
- 5.2 Material use
History
Lactic acid has historically been used both in Europe and in Asia for acidification and preservation of foods, in particular milk ( sour milk ), vegetables ( ex. sauerkraut ) and also for the production of silage as feed for centuries or millennia.
The first discovery and isolation of lactic acid goes back to the Swedish chemist Carl Wilhelm Scheele in 1780, who isolated from sour milk in the form of a brown syrup. The meat lactic acid [L- ( )- lactic acid ] was discovered by Jöns Jakob Berzelius in 1808 and its structure elucidated in 1873 by John Wislicenus. Braconnot Henri, a French chemist, in 1813 found that lactic acid can be produced in a fermentation process. 1856 Louis Pasteur discovered lactic acid bacteria and developed the basic understanding of the lactic acid fermentation. The large- scale production of lactic acid began in 1881 in the U.S., and 1895 also made the discovery, Boehringer Ingelheim, such as lactic acid using bacteria could be produced in large quantities.
Occurrence
L-( )- lactic acid is found in sweat, blood, serum in the muscle, the kidney, bile and saliva. The racemate, i.e., the 1:1 mixture of D- and L-form of lactic acid is from sour milk products, tomato juice, beer. Fungi produce lactic acid, such as members of the genera Rhizopodus, Allomyces, Blastocladiella and Others
Properties
The specific optical rotation of D- lactic acid at 20 ° C. [ α ] D20 = -2.6 (H2O) and for L- lactic acid [ α ] D20 = 2.6 (H2O). At 15 ° C a rotation [ α ] D15 = 3.82 (H2O ) is measured for L -lactic acid.
Lactic acid forming intermolecular esters. With elimination of water as dimeric compound lactoyl that weiterverestert on prolonged standing or on heating to polylactic acid. However, these macromolecules can reach no relevant chain lengths they need to use the product technically can.
In aqueous lactic acid solution, there is a chemical equilibrium between the lactic acid and its estolides. In 90 - % lactic acid solution can be found about 70 % as the free acid and 20 % as their new estolides. From two lactic acid molecules produced under the ring and elimination of two water molecules dilactide with a six-membered ring ( dilactone ). This connection is, however, not in an aqueous solution of lactic acid. From dilactides can be made using ring-opening polymerization produce quality polyester. The resulting plastic is biologically degradable and also immunologically neutral.
Production
The production of lactic acid can be carried out either via a biotechnological fermentation of carbohydrates (sugar, starch) as well as synthetically based on petrochemical raw materials (acetaldehyde ).
Fermentative production
Approximately 70 to 90 % of the world production of lactic acid is currently produced by fermentation, both pure enantiomers are commercially produced by fermentation processes using lactic acid bacteria in significant quantities. Biologically produced in the microbial fermentation of lactobacteria often the racemate of lactic acid ( 50:50 mixture ), to products with proportions from 51 to 90 % L -lactic acid.
Industrially, the production of sour milk products by fermentation of milk or whey mainly by Lactobacillus casei, Lactobacillus bulgaricus and Lactobacillus helveticus, while be used for industrial lactic acid sugar beet syrup or starch hydrolysates and Lactobacillus delbrueckii and pentose - containing liquors and Lactobacillus pentosus. The bacterial strains are classified according to their nature, glucose fermenting only to lactate or to other products: homofermentative strains such as Lactobacillus casei and Lactococcus lactis, form two moles of lactate per mole of glucose, while heterofermentative species such as Leuconostoc mesenteroides and Lactobacillus brevis, in addition to one mole of lactate per mole of glucose also produce acetic acid and ethanol.
Synthetic production
Synthetic lactic acid is produced by hydration of hydrogen cyanide ( hydrocyanic acid, HCN). Industrial scale, thereby only the synthesis of lactic acid from acetaldehyde with hydrogen cyanide over lactonitrile plays a certain role. The latter is hydrolyzed via the use of hydrochloric acid, wherein the lactic acid is produced in addition to ammonium chloride. This synthesis is realized by the Japanese company Musashino as the last large-scale producers of synthetic lactic acid.
Use
Nutrition, food and beverage
A number of foods are directly produced by lactic acid fermentation. This includes especially the sour milk products such as sour milk, yogurt, kefir and buttermilk. These are prepared by infection of pasteurized milk with starter cultures of lactic acid bacteria. Other products include lactofermentierte vegetables such as sauerkraut, beetroot borscht in some variants or Gimchi and sourdough and sourdough products accordingly. Also silages preserved by fermentation of fresh feed, based on the lactic acid fermentation.
As a food additive lactic acid carries the designation E 270 It is versatile used in the food and beverages industry as acidifier, such as in bakery, confectionery and isolated in sodas. By changing the pH value in the foods a pH of about 4, there is a preservation of the food, as a population with other microorganisms is largely excluded.
In the form of calcium lactate or calcium lactate gluconate salts can also be added for calcium fortification.
Material use
Lactic acid is the monomer of polylactic acid or polylactide (PLA ), which are widely used as biodegradable bioplastics.
Lactic acid has an antibacterial effect and is therefore liquid soaps, cleaners and dish detergents added. The disinfecting effect it develops optimum at a pH value of 3 to 4 and is also used as a means of contraception.
Lactic acid is used as a scale remover in the tanning of hides for descaling. And in the textile industry and the printing, it is used for this purpose.
Beekeepers use lactic acid for the treatment of bees against the varroa mite. Arachnologists use lactic acid to lighten the prepared epigynum of female spider or other Chitinstrukturen and to dissolve tissue residues.
The pharmaceutical technology uses lactic acid to convert water-insoluble drugs in salts of lactic acid ( lactate ); these are more soluble in water (example: Ciprofloxacin).
In cosmetics, lactic acid is used in skin creams and other products for the treatment of acne.
Physiology
Under heavy actuation of the skeletal muscle may result in increases in blood Lactatgehaltes of 5 mg / dl to 100 mg / dl. The cause is that has to be won in anaerobic conditions, such as during rapid activation of the skeletal muscle, energy in the form of NAD from the reduction of pyruvate by lactate dehydrogenase for the continuation of glycolysis. The thereby obtained lactic acid (lactate and H ) is flushed through the monocarboxylate transporter 1 from the cells. This process was previously understood as a cause of muscle soreness, but this theory is now largely considered to be wrong.
For humans, the dextrorotatory L-( )- lactic acid is the physiological. Taken orally it is decomposed rapidly in the body than the levorotatory D-(- ) -lactic acid.