Monosodium glutamate
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.[2][3][4] MSG is used in cooking as a flavor enhancer with a savory taste that intensifies the meaty, savory flavor of food, as naturally occurring glutamate does in foods such as stews and meat soups.[5][6]
This article is about the chemical compound. For its use in food, see Glutamate flavoring.
MSG was first prepared 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) for Japanese cuisine. MSG balances, blends, and rounds the perception of other tastes.[7][8] 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.[9] 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.[9][10][11] The European Union classifies it as a food additive permitted in certain foods and subject to quantitative limits. MSG has the HS code 29224220 and the E number E621.[12]
Use[edit]
Pure MSG is reported not to have a highly pleasant taste until it is combined with a savory aroma.[13] The basic sensory function of MSG is attributed to its ability to enhance savory taste-active compounds when added in the proper concentration.[7] 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.[14]
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.[15] Although other salts of glutamate have been used in low-salt soups, they are less palatable than MSG.[16] Food scientist Steve Witherly noted in 2017 that MSG may promote healthy eating by enhancing the flavor of food such as kale while reducing the use of salt.[17]
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).[18]
Production[edit]
MSG has been produced by three methods: hydrolysis of vegetable proteins with hydrochloric acid to disrupt peptide bonds (1909–1962); direct chemical synthesis with acrylonitrile (1962–1973), and bacterial fermentation (the current method).[36] Wheat gluten was originally used for hydrolysis because it contains more than 30 g of glutamate and glutamine in 100 g of protein. As demand for MSG increased, chemical synthesis and fermentation were studied. The polyacrylic fiber industry began in Japan during the mid-1950s, and acrylonitrile was adopted as a base material to synthesize MSG.[37]
As of 2016, most MSG worldwide is produced by bacterial fermentation in a process similar to making vinegar or yogurt. Sodium is added later, for neutralization. During fermentation, Corynebacterium species, cultured with ammonia and carbohydrates from sugar beets, sugarcane, tapioca or molasses, excrete amino acids into a culture broth from which L-glutamate is isolated. Kyowa Hakko Kogyo (currently Kyowa Kirin) developed industrial fermentation to produce L-glutamate.[38]
The conversion yield and production rate (from sugars to glutamate) continues to improve in the industrial production of MSG, keeping up with demand.[36] The product, after filtration, concentration, acidification, and crystallization, is glutamate, sodium, and water.
Chemical properties[edit]
The compound is usually available as the monohydrate, a white, odorless, crystalline powder. The solid contains separate sodium cations Na+
and glutamate anions in zwitterionic form, −OOC-CH(NH+
3)-(CH
2)2-COO−.[39] In solution it dissociates into glutamate and sodium ions.
MSG is freely soluble in water, but it is not hygroscopic and is insoluble in common organic solvents (such as ether).[40] It is generally stable under food-processing conditions. MSG does not break down during cooking and, like other amino acids, will exhibit a Maillard reaction (browning) in the presence of sugars at very high temperatures.[41]
History[edit]
Glutamic acid was discovered and identified in 1866 by the German chemist Karl Heinrich Ritthausen, who treated wheat gluten (for which it was named) with sulfuric acid.[42] Kikunae Ikeda of Tokyo Imperial University isolated glutamic acid as a taste substance in 1908 from the seaweed Laminaria japonica (kombu) by aqueous extraction and crystallization, calling its taste umami ("delicious taste").[43][44] Ikeda noticed that dashi, the Japanese broth of katsuobushi and kombu, had a unique taste not yet scientifically described (not sweet, salty, sour, or bitter).[43] To determine which glutamate could result in the taste of umami, he studied the taste properties of numerous glutamate salts such as calcium, potassium, ammonium, and magnesium glutamate. Of these salts, monosodium glutamate was the most soluble and palatable, as well as the easiest to crystallize.[45] Ikeda called his product "monosodium glutamate" and submitted a patent to produce MSG;[46] the Suzuki brothers began commercial production of MSG in 1909 using the term Ajinomoto ("essence of taste").[36][41][47]