Monosodium glutamate (MSG), also known as sodium glutamate, is a sodium salt of glutamic acid. MSG is found naturally in some foods including tomatoes and cheese in this glutamic acid form, and is used in cooking as a flavor enhancer that intensifies the umami flavor of food, as naturally occurring glutamate does in foods such as stews and meat soups. MSG was first extracted in 1908 by Japanese biochemist Kikunae Ikeda, who tried to isolate and duplicate the savory taste of kombu, an edible seaweed used as a broth (dashi) ingredient in Japanese cuisine. It also balances, blends, and rounds the perception of other tastes. MSG, along with disodium ribonucleotides, is commonly used and found in stock (bouillon) cubes, soups, ramen, gravy, stews, condiments, savory snacks, etc. The U.S. Food and Drug Administration has given MSG its generally recognized as safe (GRAS) designation. It is a popular misconception that MSG can cause headaches and other feelings of discomfort, known as "Chinese restaurant syndrome". Several blinded studies show no such effects when MSG is combined with food in normal concentrations, and are inconclusive when MSG is added to broth in large concentrations. The European Union classifies it as a food additive permitted in certain foods and subject to quantitative limits. MSG has the HS code 2922.42 and the E number E621.
Use Pure MSG is reported to have a highly unpleasant taste until it is combined with a savory aroma. The basic sensory function of MSG is attributed to its ability to enhance savory taste-active compounds when added in the proper concentration. The optimal concentration varies by food; in clear soup, the "pleasure score" rapidly falls with the addition of more than one gram of MSG per 100 mL. The sodium content (in mass percent) of MSG, 12.28%, is about one-third of that in sodium chloride (39.34%), due to the greater mass of the glutamate counterion, and the remainder, 87.72%, is glutamic acid. Although other salts of glutamate have been used in low-salt soups, they are less palatable than MSG. The ribonucleotide food additives disodium inosinate (E631) and disodium guanylate (E627), as well as conventional salt, are usually used with monosodium glutamate-containing ingredients as they seem to have a synergistic effect. "Super salt" is a mixture of 9 parts salt, to one part MSG and 0.1 parts disodium ribonucleotides (a mixture of disodium inosinate and disodium guanylate).
Safety MSG is generally recognized as safe to eat. A popular belief is that MSG can cause headaches and other feelings of discomfort, but blinded tests have not provided strong evidence of this. International bodies governing food additives currently consider MSG safe for human consumption as a flavor enhancer. Under normal conditions, humans can metabolize relatively large quantities of glutamate, which is naturally produced in the gut in the course of protein hydrolysis. The median lethal dose (LD50) is between 15 and 18 g/kg body weight in rats and mice, respectively, five times the LD50 of table salt (3 g/kg in rats). The use of MSG as a food additive and the natural levels of glutamic acid in foods are not of toxic concern in humans. Specifically MSG in the diet does not increase glutamate in the brain or affect brain function. A 1995 report from the Federation of American Societies for Experimental Biology (FASEB) for the United States Food and Drug Administration (FDA) concluded that MSG is safe when "eaten at customary levels" and, although a subgroup of otherwise-healthy individuals develop an MSG symptom complex when exposed to 3 g of MSG in the absence of food, MSG as a cause has not been established because the symptom reports are anecdotal. According to the report, no data support any role of glutamate in chronic disease. High quality evidence has failed to demonstrate a relationship between the MSG symptom complex and actual MSG consumption. No association has been demonstrated, and the few responses were inconsistent. No symptoms were observed when MSG was used in food. Adequately controlling for experimental bias includes a blinded, placebo-controlled experimental design and administration by capsule, because of the unique aftertaste of glutamates. In a 1993 study, 71 fasting participants were given 5 g of MSG and then a standard breakfast. One reaction (to the placebo, in a self-identified MSG-sensitive individual) occurred. A study in 2000 tested the reaction of 130 subjects with a reported sensitivity to MSG. Multiple trials were performed, with subjects exhibiting at least two symptoms continuing. Two people out of the 130 responded to all four challenges. Because of the low prevalence, the researchers concluded that a response to MSG was not reproducible. Studies exploring MSG's role in obesity have yielded mixed results. Although several studies have investigated anecdotal links between MSG and asthma, current evidence does not support a causal association.
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