Malic acid (formula NOOSSN2CH (OH) COOH), hydroxy succinic, dibasic hydroxycarboxylic (fruit) acid. It is represented by a colorless crystalline substance. Malic acid is readily soluble in ethanol and water, and poorly in ether.
The substance has cleansing, antioxidant, anti-inflammatory, moisturizing and mild astringent properties.
Classification of acids NOOSSN2CH (OH) COOH
Under natural conditions, L-malic acid is common. Melting point - one hundred degrees. It is well dissolved in water. In ethanol, the solubility is 68.3 g, in diethyl ether - 1.9 g per hundred grams of solvent.
D-malic acid has a melting point of 130.8 degrees. Solubility in ethanol - 35.9 g, in diethyl ether - 0.6 g per hundred grams of solvent.
Both substances are insoluble in benzene.
Malic acid is endowed with the chemical properties of hydroxy acids. Its salts and esters are called malates. When heated to one hundred degrees, malic acid is converted to an anhydride identical to lactides. Longer heating (up to 140-150 degrees) contributes to the cleavage of water. As a result, malic acid is converted to fumaric acid, and with rapid heating to one hundred eighty degrees, maleic anhydride is also formed.
NOOSSN2CH (OH) COOH is considered one of the important intermediate components of metabolic processes in living organisms. Malic acid is involved in metabolism in the form of malate. It is formed in the cycle of tricarboxylic acids, with gluconeogenesis. Malate after enzymatic reactions can turn into pyruvate, fumarate, oxaloacetate.
HOOCCH2CH (OH) COOH is obtained by reducing grape acid by hydrolysis of D, L-bromosuccinic acid.
In industry, NOOSSN2CH (OH) COOH is used in the manufacture of confectionery and fruit water. Malic acid is also used in winemaking. The substance is used as a pH regulator and flavoring agent.
Malic acid (D, L) is obtained by the reduction of oxalylacetic acid with NOOCCOCH2COOH by the amalgam Na or by hydrolysis of its (oxalylacetic acid) reduced esters.
In nature, the substance is found in acidic fruits. These include, in particular, unripe apples, fruits of mountain ash, gooseberries, and rhubarb. In tobacco, malic acid is in the form of calcium salt. In a small amount, it can also be found in wine. In nature, NOOSSN2CH (OH) COOH is formed due to the incomplete process of sugar oxidation. Especially in large quantities, malic acid can be found in unripe grapes (from thirteen to fifteen grams per dm3). In the process of ripening berries, the amount of NOOSSN2CH (OH) COOH decreases to two to five grams per dm3. This decrease in concentration is due to the fact that the substance takes an active part in the respiratory processes. It should be noted that more malic acid was found in grapes from the northern regions than in fruits from the southern regions. The content of NOOSSN2CH (OH) COOH also depends on weather conditions throughout the year and on the grape variety itself.
With alcoholic fermentation, about twenty-five percent of malic acid absorbs yeast. In the process, alcohol is formed and carbon dioxide is released. Bacterial fermentation results in the formation of highly pure succinic acid. The condensation of OO2 () COOH and urea is the basis for the synthesis of uracil (a component of RNA).
Under the influence of lactic acid bacteria, malic acid can decompose to lactic acid. NOOSSN2CH (OH) COOH affects the taste of wine. The high content of malic acid causes a "green acidity" - a pungent taste. In these cases, a biological "acid reduction" is carried out. The principle of the process is based on the ability of yeast and lactic acid bacteria to absorb OO2 () COOH.