Lactic acid is one of the hydroxycarboxylic acids. It forms an important product of metabolism.
What is lactic acid?
Lactic acid (Acidum lacticum) is an organic acid. It belongs to the hydroxycarboxylic acids and is thus an alkanoic acid. It has both a hydroxy group and a carboxy group. Lactic acid is also known as 2-hydroxypropanoic acid or 2-hydroxyproprionic acid. The esters and salts of the acid are called lactates. In the form of lactate, lactic acid represents an important metabolic intermediate. This primarily includes lactic acid fermentation and sugar breakdown. In the entire world, approximately 250,000 tons of lactic acid are produced every year. Most of this is used in the food industry. Lactic acid was first discovered in 1780 by the German-Swedish chemist Carl Wilhelm Scheele (1742-1786). He isolated it from sour milk. In 1808, the Swede Jöns Jakob Berzelius (1779-1848) also discovered meat lactic acid. In 1856, Louis Pasteur (1822-1895) finally discovered lactic acid bacteria, which led to the development of an understanding of lactic acid fermentation. From 1881, large-scale production of lactic acid took place in the USA. With the help of bacteria, large quantities of lactic acid can be produced since then.
Function, effect and tasks
Lactic acid comes in two varieties. A distinction is made between dextrorotatory and levorotatory lactic acid. The difference between the two forms is different arranged atoms, which also results in different physical properties. The designation “rotational” goes back to physical light properties. When the lactic acid is brought under polarizing light, a rotation of the light beam occurs either in the right or in the left direction. The dextrorotatory lactic acid (L(+) lactic acid) also bears the name physiological lactic acid because it can be readily utilized by the human organism. It is also one of the metabolic waste products of the human body. With the help of dextrorotatory lactic acid, energy can be obtained within the metabolism. Another function is the protection of the intestinal mucosa. In contrast, left-handed lactic acid (D(-)-lactic acid) requires conversion by an enzyme before it can be digested. Thus, unphysiological left-handed lactic acid, which is ingested with food, is difficult for the human body to digest. Lactic acid is not of essential importance to humans. However, it and lactic acid products have some health-promoting effects. Dextrorotatory lactic acid is important for metabolism. Among other things, it ensures the production of energy in the red blood cells, liver and muscles. Furthermore, it serves as a starting material for building steroids, fatty acids and glucose. Furthermore, lactic acid represents an important protection for the human intestinal flora. It ensures that pathogens cannot spread. Bacterial lactic acid also performs this task in female vaginal secretions. The same applies to the protective acid mantle on the skin, of which lactic acid is a component. For this reason, lactic acid is also used as a natural remedy. In contrast to dextrorotatory lactic acid, levorotatory lactic acid is used only for energy production. Its conversion from food is much slower. In addition, it causes a slower metabolism.
Formation, occurrence, properties, and optimal values
In the human body, dextrorotatory lactic acid is formed primarily in blood, sweat and saliva. Furthermore, it is produced in bile, kidney and muscle serum. In the organism, lactic acid is formed through exercise and intense physical exertion. In the muscles, lactate is produced, which is the salt of lactic acid. Lactate, in turn, is produced from glucose (dextrose) if oxygen is not available. Physicians also refer to this process as anerobic glycolysis. An elevated lactate level is also considered an indication of the development of certain diseases. These include infections, diabetes mellitus, brain injuries and pulmonary embolism. A lactate or lactic acid value of 0.5 to 2.2 millimoles per liter within the blood plasma is considered normal. In the fluid of the spinal cord (cerebrospinal fluid), the reference value is 1.1 to 2.4 millimoles per liter.Intensive sport or hard physical work causes these values to rise. The same applies to metabolic derailments in the case of diabetes and serious illnesses such as cardiac insufficiency. If the lactic acid values are too low, this does not represent a disease value. Lactic acid fermentation also produces popular sour milk products such as yogurt, sour milk, buttermilk and kefir. In addition, lactic acid serves as a versatile acidifier in the food industry.
Diseases and disorders
Negative effects on human metabolism caused by a diet containing levorotatory lactic acid have not been reported in healthy individuals. However, it is recommended not to consume too much nonphysiological lactic acid. For example, there is a risk of lactic acidosis in risk groups. This is a metabolic disorder triggered by the accumulation of levorotatory lactic acid. In the case of diabetes or liver damage, it can lead to the aggravation of an already existing acidosis. Adverse effects on human health are also sometimes seen in cases of circulatory disease or elevated uric acid levels. This risk also exists in competitive athletes. Infants must not be given left-handed lactic acid. The reason for this is their still immature metabolism. However, lactic acid products composed of dextrorotatory lactic acid do not pose a health risk and are considered particularly recommendable. For this reason, dextrorotatory lactic acid is a generally approved food without restrictions.
