What is lactic acid?
Lactic acid is an organic compound with the formula C3H6O3. The pure substance is fixed, but the racemic mixture occurs as a colorless hygroscopic oily liquid, which is readily soluble in water. Lactic acid is a substance which is released, inter alia, in various biological processes. Lactic acid has E number E270.
Structure and properties
Lactic acid is a carboxylic acid, more particularly a hydroxycarboxylic acid, that gives her milk acidified sour taste and which during heavy exercise by anaerobic degradation of sugar builds up in the muscles, and it allows for temporary muscle pain. In neutral and basic environment (pKa = 3.85), hence also in the body, lactic acid dissociates into a lactate ion, and a negatively charged H + ion. The acidification is not the result of the lactate which is formed. Lactate is namely, a substrate that can be used to form glucose in the liver by the gluconeogenesis. The acidification in the muscles is the result of a build-up of H + ions which no longer can be buffered by bicarbonate.
Lactic acid is a chiral molecule. Due to the presence of a stereogenic center there are two enantiomers. On the basis of their different optical activity is also known as D-lactic acid levorotatory lactic acid, and L-lactic acid also called dextrorotatory lactic acid. Turning refers to the direction in which the enantiomer can change the polarization of light.
D- and L-lactic acid are metabolized differently by the body. Dextrorotatory lactic acid is readily metabolized by the body, since it is structurally identical to the lactic acid that (among other things) is produced in muscle tissue. Counterclockwise lactic acid is not the body, but can (albeit slower) are processed by the body. It is eventually excreted through urine and sweat. Babies and young children are not able to handle larger amounts of levorotatory lactic acid, which is why it is recommended to parents to give their products that contain dextrorotatory lactic acid.
Fermentation
Fermentation in the body
Under anaerobic conditions, L-lactic acid is formed from pyruvic acid via the enzyme lactic dehydrogenase. In this reaction, NADH is oxidized to NAD +.
These include lactic fermentation takes place in the red blood cells, because they have no mitochondria, but also during heavy exercise in muscle, because muscle gain during strenuous exercise for aerobic dissimilation of sugar enough oxygen.
The L-lactic acid enters the bloodstream and is on average under normal conditions 1 to 2 mmol / L, but during heavy exercise may take up to twenty times as much. The liver accounts for 60 at% of the L-lactic acid, and converts it into glycogen, which is converted back into glucose by glycogenolysis. The glucose released into the blood and can be used again by the body. This cycle, for the first time described by Carl and Gerty Cori, is known as the Cori cycle. The remaining 40% of the lactic acid is converted into pyruvic acid by the muscle cells, which is processed with the aid of oxygen in the citric acid cycle and electron transport chain.
Bacterial fermentation
Lactic acid bacteria form lactic acid by fermentation, the sour taste of causes include soured milk. They are also used in the preparation of milk products such as yoghurt, cheese, kefir, as well as in the manufacture of fermentation products, such as sauerkraut, and other fermented starch products. Fermented (whether or not organic) fruit juices also contain lactic acid. Lactic acid also results from malolactic fermentation of wine, with the sharp-tasting malic acid is converted to the milder-tasting lactic acid.
Some species of lactic acid bacteria (Lactobacillus casei) only or mainly to make the left-handed form, some of the right-handed form (Lactobacillus delbrueckii ssp. Bulgaricus), and some both forms (the racemic mixture, including Lactobacillus acidophilus).
This process is also carried out on an industrial scale. Usually granulated sugar used as raw material, which is converted by bacteria into lactic acid. After purification, the product is sold or further processed into derived products, such as lactate. World's largest producer of lactic acid Purac.
Lactic acid bacteria in the mouth to cause the formation of lactic acid by tooth decay.
Raw material for polymers
Lactic acid is more and more used for the production of biodegradable polymer (polylactic acid). The polymerization is normally carried out with lactic acid, but not with the cyclic dimer of lactic acid: lactide. These polymers from renewable raw materials were initially mainly used in special applications such as in surgery (sutures decompose over time and do not need to be removed), but they also more often used as a substitute of traditional plastics from petroleum chemicals.