Monosodium Glutamate (MSG)
Characteristics of MSG
Monosodium glutamate (MSG), a compound represented by the formula C5H8NNaO4 • H2O, is a sodium salt of the naturally occurring glutamic acid. Glutamic acid, first isolated in 1886, became an important industrial chemical when its sodium salt was found to enhance the flavor of certain foods. The elements that make up the MSG molecule can exist in two different forms, known as isomers, and only one form has the flavor enhancing effect. It is believed by some that MSG is responsible for a disease known as "Chinese Restaurant Syndrome." Subsequent studies however, have not established a direct link between MSG and this disease.
The identification of MSG began with the isolation of glutamic acid from a mass of wheat protein, called gluten, in 1886. The chemical structure of glutamic acid, a naturally occurring amino acid, was later identified in 1890. The flavor enhancing ability of MSG was discovered by the Japanese chemist Ikeda Kibunae (1864-1936). From a kelplike seaweed, which was traditionally used to add flavor to Japanese food, he isolated MSG and patented a method for its production in 1908. Commercial production of this flavor-enhancing agent soon followed and Japan's first major chemical industry was born.
In 1968, the safety of MSG came into question when a largely anecdotal report was published that suggested MSG caused a disease commonly referred to as "Chinese restaurant syndrome" (CRS). This disease was said to produce symptoms of burning, numbness, fever, and a tightness in the upper body. Although many subsequent studies failed to show any link between MSG and these symptoms, the safety of MSG as a food additive continues to be questioned by some.
The three methods for producing MSG that are most often employed are vegetable proteinhydrolysis, microbial fermentation, and organic synthesis. Obtaining MSG by the hydrolysis of vegetable proteins is the oldest method of production. In this method, waste protein, such as wheat gluten and beet sugar molasses, is placed in water and heated in the presence of an acid. Under these conditions, the peptide bonds—chemical bonds that connect the amino acids in the proteins—are broken. Each individual amino acid can then be isolated by a method known as crystallization. Glutamic acid crystals can be converted to the MSG by reacting them with sodium hydroxide. Another method of production requires the use of microorganisms that are capable of producing MSG. Bacteria such as Micrococcus glutamicus have the ability to convert some carbohydrates into amino acids. Glutamic acid is one of these amino acids, and it can be isolated, then converted to MSG by partial neutralization. MSG can also be produced synthetically by an organic reaction based on acrylate.
At room temperature, MSG (C5H8NNaO4• H2O) is a salt, which typically exists as a white, odorless crystalline powder that is soluble in water and alcohol. It does not have a melting point per se, but it decomposes when it is heated. When crystals of MSG are created in a water solution, they develop in the shape of rhombic prisms.
The molecules of MSG can exist in two different forms known as isomers. These isomers are chemically identical, but physically different because their molecular structures are dissimilar. In fact, the elements on the two MSG isomers, known as stereoisomers, are arranged in such a way that if they were placed next to each other, they would appear as mirror images. The isomers of MSG have different physiological effects, and only one of them, known as the L form, has flavor enhancing properties.
Although MSG is tasteless by itself, it is a flavor enhancer that can be used to improve the taste of meat, fish, fowl, vegetables, and soup. It is said to provide a unique flavor that is neither bitter, sour, sweet, or salty. Typically employed at concentrations of 0.2-0.9%, it is used extensively by the food industry in canned, frozen, and dried foods and Oriental food. It has also been used, with sugar, to improve the palatability of bitter drugs.
Filer, L. J. Glutamic Acid: Advances in Biochemistry and Physiology. New York: Raven Press, 1979.
Othmer, Kirk. Encyclopedia of Chemical Technology. Vol. 2. New York: Wiley, 1978.