Глутаминовая кислота-L

Описание

L-Glutamic acid, or L-2-aminopentanedioic acid, is a naturally occurring amino acid of plant and animal proteins. It has a very faint odor reminiscent of yeast or freshly baked bread. It has a mild, somewhat sweet, meat-like taste.
The average glutamic acid content of food proteins is 20 percent. Expressed as glutamic acid per 100 g of the edible portions, medium fat beef contains about 2.65 g of glutamic acid; whole liquid cow milk, 0.82 g; lean pork, 2.16 g; haddock, 2.32 g; peas, 5.58 g; soybeans, 7.01 g; commeal, 1.62 g; and whole grain wheat flour, 4.16 g. In addition, free glutamic acid is present in many vegetables, fish, and meats in small amounts (0. 005 to 0.23 g per 100 g) and as high as 2 g per 100 g in some varieties of cheese. Recent estimates of free amino acids in the milk of various species indicated that the free glutamic acid in human milk is about 0.22 g per 100 mL.
Glutamic acid and its salts are prepared commercially by hydrolysis of gluten (wheat, corn, soybean, sugarbeet protein); by fermentation from glucose-containing raw materials; the racemic acid may be resolved into the d- and ι-isomer by fractional crystallization; from 2 -cyclopentenylamine; by microbial conversion of aketoglutaric acid; or by an alternative method, using Bacillus megatherium-cereus; from fumaric acid using B. pumilus; from starch.
Glutamic acid and the hydrochloride as well as the mono-sodium, -potassium, and -ammonium salts of L-glutamic acid share similar physical properties: they are nearly odorless, white, free-flowing crystalline powders, and except for glutamic acid and glutamic acid hydrochloride, are freely soluble in water. Glutamic acid is slightly soluble and glutamic acid hydrochloride moderately soluble in water. The pH of a saturated solution is about 3.2.

Химические свойства

L-Glutamic acid has a very faint odor reminiscent of yeast or freshly baked bread and a mild, somewhat sweet, meat- like taste This is a naturally occurring amino acid of plant and animal proteins The average glutamic acid content of food proteins is 20%, expressed as glutamic acid per 100 g of the edible portions For a detailed description, see Burdock (1997).

Вхождение

Reported as occurring in many vegetable proteins, in beef fbrin, in the chrysalis of silkworm, in the hydro- lysate of crystalline insulin Also present in other important peptides, such as glutathione, tyrocidin, folic acid, β-lactoglobulin, secretin and bacitracin, and in growth hormone

Использование

L-glutamic acid or its salt, monosodium glutamate (MSG), is used as an additive to human food to enhance the taste. Although seaweed had been used in Asia to enhance food flavor for over 1000 years, it was not until 1908 that the essential component responsible for the flavor phenomenon was identified as glutamic acid. From 1910 until 1956, monosodium glutamate was extracted from sea weed, a slow and costly method. In 1956, Ajinomoto, a Japanese company, succeeded in producing glutamic acid by means of fermentation. Today, L-glutamic acid or MSG is generally made by microbial fermentation using genetically modified bacteria.

Определение

ChEBI: An optically active form of glutamic acid having L-configuration.

Подготовка

By hydrolysis of gluten (wheat, corn or other vegetable sources); by fermentation from glucose-containing raw materials; the racemic acid may be resolved into the d- and l-isomer by fractional crystallization; from 2-cyclopentenylamine; by microbial conversion of α-ketoglutaric acid; or by an alternative method, using Bacillus megatherium-cereus; from fumaric acid, using B pumilus; from starch.

Биотехнологическое производство

For industrial production of L-glutamic acid, molasses (sucrose), starch hydrolysates (glucose) and ammonium sulfate are generally used as carbon and nitrogen sources, respectively. Key factors in controlling the fermentation are the presence of biotin in optimal concentration – to optimize cell growth and the excretion of Lglutamate – and sufficient supply of oxygen to reduce the accumulation of byproducts, such as lactic and succinic acid. In biotin-rich fermentation media the addition of penicillin or cephalosporin C favors the overproduction of L-glutamic acid due to effects on the cell membrane. The supplementation of fatty acids also results in an increased permeability of the cells thus enhancing glutamate excretion.
A strain of Microbacterium ammoniaphilum cultured under biotin-deficient conditions produced 58 % of L-glutamic acid formed from glucose via phosphoenolpyruvate, citrate, and of a-ketoglutarate and the other 42 % via the tricarboxylic acid (TCA) or the glyoxylate cycle.

Биологическая активность

The predominant excitatory transmitter in the mammalian central nervous system. Acts at ionotropic and metabotropic glutamate receptors.

Профиль безопасности

Human systemic effects by ingestion and intravenous routes: headache and nausea or vomiting. When heated to decomposition it emits toxic fumes of NOx.

Методы очистки

Crystallise L-glutamic acid from H2O acidified to pH 3.2 by adding 4volumes of EtOH, and drying at 110o. Likely impurities are aspartic acid and cysteine. It sublimes at 170-175o/10mm. It melts at 160o with cyclisation to L-pyrrolidone carboxylic acid. [Dunn & Brophy J Biol Chem 99 224 1958, Parikh et al. J Am Chem Soc 80 9571958, Greenstein & Winitz The Chemistry of the Amino Acids J. Wiley, Vol 3 pp 1929-1952 1961, Beilstein 4 III 1530, 4 IV 3028.]