Monosodium glutamate (MSG), also known assodium glutamate, is asodiumsalt ofglutamic acid. MSG is found naturally in some foods includingtomatoes andcheese in this glutamic acid form.[2][3][4] MSG is used in cooking as a flavor enhancer with a savory taste that intensifies theumami flavor of food, as naturally occurring glutamate does in foods such asstews and meat soups.[5][6]
Pure MSG is reported not to have a highly pleasant taste until it is combined with a savoryaroma.[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; inclear soup, the "pleasure score" rapidly falls with the addition of more than one gram of MSG per 100mL.[14]
The sodium content (inmass percent) of MSG, 12.28%, is about one-third of that insodium 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 askale while reducing the use ofsalt.[17]
MSG isgenerally recognized as safe to eat.[2][19] A popular belief is that MSG can cause headaches and other feelings of discomfort, butblinded tests have not provided strong evidence of this.[10] International bodies governing food additives currently consider MSG safe for human consumption as a flavor enhancer.[20] Under normal conditions, humans can metabolize relatively large quantities of glutamate, which is naturally produced in the gut in the course of protein hydrolysis. Themedian lethal dose (LD50) is between 15 and 18 g/kg body weight in rats and mice, respectively, five times the LD50 oftable 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.[20] Specifically MSG in the diet does not increase glutamate in the brain or affect brain function.[21]
A 1995 report from theFederation of American Societies for Experimental Biology (FASEB) for theUnited 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.[22]
According to the report, no data supports the role of glutamate inchronic 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.[23][24][25][26]
Adequately controlling for experimental bias includes a blinded,placebo-controlledexperimental design and administration by capsule, because of the unique aftertaste of glutamates.[25] 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.[23] 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.[27]
Studies exploring MSG's role inobesity have yielded mixed results.[28][29]
Although several studies have investigated anecdotal links between MSG andasthma, current evidence does not support a causal association.[30]
"There is no convincing evidence that MSG is a significant factor in causing systemic reactions resulting in severe illness or mortality. The studies conducted to date on Chinese restaurant syndrome (CRS) have largely failed to demonstrate a causal association with MSG. Symptoms resembling those of CRS may be provoked in a clinical setting in small numbers of individuals by the administration of large doses of MSG without food. However, such effects are neither persistent nor serious and are likely to be attenuated when MSG is consumed with food. In terms of more serious adverse effects such as the triggering ofbronchospasm in asthmatic individuals, the evidence does not indicate that MSG is a significant trigger factor."[31][32]
However, the FSANZ MSG report says that although no data is available on average MSG consumption in Australia and New Zealand, "data from the United Kingdom indicates an average intake of 590mg/day, with extreme users (97.5th percentile consumers) consuming 2,330mg/day" (Rhodes et al. 1991).[33] In a highly seasoned restaurant meal, intakes as high as 5,000 mg or more may be possible (Yang et al. 1997).[34] When very large doses of MSG (>5 g MSG in abolus dose) are ingested, plasma glutamate concentration will significantly increase. However, the concentration typically returns to normal within two hours. In general, foods providing metabolizablecarbohydrates significantly attenuate peak plasma glutamate levels at doses up to 150mg/kg body weight. Two earlier studies – the 1987 JointFAO/WHO Expert Committee on Food Additives (JECFA) and the 1995Federation of American Societies for Experimental Biology (FASEB) – concluded, "there may be a small number of unstable asthmatics who respond to doses of 1.5–2.5 g of MSG in the absence of food". The FASEB evaluation concluded, "sufficient evidence exists to indicate some individuals may experience manifestations of CRS when exposed to a ≥3 g bolus dose of MSG in the absence of food".[31]
MSG has been produced by three methods:hydrolysis of vegetable proteins with hydrochloric acid to disruptpeptide bonds (1909–1962); direct chemical synthesis withacrylonitrile (1962–1973), andbacterial fermentation (the current method).[35]Wheat gluten was originally used forhydrolysis because it contains more than 30 g of glutamate and glutamine per 100 g of protein. As demand for MSG increased, chemical synthesis and fermentation were studied. Thepolyacrylic fiber industry began in Japan during the mid-1950s, andacrylonitrile was adopted as a base material to synthesize MSG.[36]
As of 2016, most MSG worldwide is produced bybacterial fermentation in a process similar to making vinegar or yogurt.Sodium is added later, for neutralization. During fermentation,Corynebacterium species, cultured withammonia andcarbohydrates fromsugar beets,sugarcane,tapioca ormolasses, excrete amino acids into a culture broth from which L-glutamate is isolated. Kyowa Hakko Kogyo (currentlyKyowa Kirin) developed industrial fermentation to produce L-glutamate.[37]
The conversion yield and production rate (from sugars to glutamate) continues to improve in the industrial production of MSG, keeping up with demand.[35] The product, after filtration, concentration, acidification, and crystallization, is glutamate, sodium ions, and water.
The compound is usually available as themonohydrate, a white, odorless, crystalline powder. The solid contains separate sodium cationsNa+ and glutamate anions inzwitterionic form,−OOC-CH(NH+ 3)-(CH 2)2-COO−.[38] In solution itdissociates into glutamate and sodium ions.
MSG is freely soluble in water, but it is nothygroscopic and is insoluble in common organic solvents (such asether).[39] It is generally stable under food-processing conditions. MSG does not break down during cooking and, like other amino acids, will exhibit aMaillard reaction (browning) in the presence of sugars at very high temperatures.[40]
Glutamic acid was discovered and identified in 1866 by the German chemistKarl Heinrich Ritthausen, who treated wheatgluten (for which it was named) withsulfuric acid.[41]Kikunae Ikeda ofTokyo Imperial University isolated glutamic acid as a taste substance in 1908 from the seaweedLaminaria japonica (kombu) by aqueous extraction and crystallization, calling its tasteumami ("delicious taste").[42][43] Ikeda noticed thatdashi, the Japanese broth ofkatsuobushi andkombu, had a unique taste not yet scientifically described (not sweet, salty, sour, or bitter).[42] To determine which glutamate could result in the taste ofumami, 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.[44] Ikeda called his product "monosodium glutamate" and submitted apatent to produce MSG;[45] the Suzuki brothers began commercial production of MSG in 1909 using the termAjinomoto ("essence of taste").[35][40][46]
MSG is one of several forms of glutamic acid found in foods, in large part because glutamic acid (an amino acid) is pervasive in nature. Glutamic acid and its salts may be present in a variety of other additives, includinghydrolyzed vegetable protein,autolyzed yeast,hydrolyzed yeast,yeast extract,soy extracts, and protein isolate, which must be specifically labeled. Since 1998, MSG cannot be included in the term "spices and flavorings". However, the term "natural flavor/s" is used by the food industry for glutamic acid (chemically similar to MSG, lacking only the sodiumion). TheFood and Drug Administration (FDA) does not require disclosure of components and amounts of "natural flavor/s."[47]
Standard 1.2.4 of the Australia and New Zealand Food Standards Code requires MSG to be labeled in packaged foods. The label must have the food-additive class name (e.g. "flavour enhancer"), followed by the name of the additive ("MSG") or itsInternational Numbering System (INS) number, 621.[48]
ThePunjab Food Authority banned Ajinomoto, commonly known as Chinese salt, which contains MSG, from being used in food products in thePunjab Province of Pakistan in January 2018.[49]
The prohibition against the import and manufacture of MSG was enforced on 28 February 2018, following an order by the Supreme Court on 10 February 2018.[50]
The controversy surrounding the safety of MSG started with the publication of Robert Ho Man Kwok's correspondence letter titled "Chinese-Restaurant Syndrome" in theNew England Journal of Medicine on 4 April 1968.[59][60] In his letter, Kwok suggested several possible causes before he nominated MSG for his symptoms.[61][23] This letter was initially met with insider satirical responses, often usingrace as prop for humorous effect, within the medical community.[59] During the discursive uptake in media, the conversations were recontextualized as legitimate while the race-based motivations of the humor were not parsed, which replicated historical racial prejudices.[59]
Despite the resulting public backlash, theFood and Drug Administration (FDA) did not remove MSG from their Generally Recognized as Safe list.[62] In 1970, a National Research Council under theNational Academy of Science, on behalf of the FDA, investigated MSG but concluded that MSG was safe for consumption.[62]
The controversy about MSG is tied to racial stereotypes against East Asian societies.[62][63][64][65][66] Herein, specificallyEast Asian cuisine was targeted, whereas the widespread usage of MSG in Western processed food does not generate the same stigma.[67] These kind of perceptions, such as the rhetoric of the so-called Chinese restaurant syndrome, have been attributed to xenophobic or racist biases.[68][69][70][71][72][73]
Food historian Ian Mosby wrote that fear of MSG in Chinese food is part of the US's long history of viewing the "exotic" cuisine of Asia as dangerous and dirty.[74] In 2016,Anthony Bourdain stated inParts Unknown that "I think MSG is good stuff ... You know what causes Chinese restaurant syndrome? Racism."[75]
In 2020,Ajinomoto, the leading manufacturer of MSG, and others launched the #RedefineCRS campaign, in reference to the term "Chinese restaurant syndrome", to combat the misconceptions about MSG, saying they intended to highlight the xenophobicprejudice againstEast Asian cuisine and the scientific evidence.[76] Following the campaign, Merriam-Webster announced it would review the term.[77]
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^Walker R (October 1999). "The significance of excursions above the ADI. Case study: monosodium glutamate".Regul. Toxicol. Pharmacol.30 (2 Pt 2): S119–21.doi:10.1006/rtph.1999.1337.PMID10597625.
^Bakalar, Nicholas (25 August 2008)."Nutrition: MSG Use is Linked to Obesity".The New York Times. Retrieved10 November 2010.Consumption of monosodium glutamate, or MSG, the widely used food additive, may increase the likelihood of being overweight, a new study says.
^Yoshida T (1970). "Industrial manufacture of optically active glutamic acid through total synthesis".Chemie Ingenieur Technik.42 (9–10):641–44.doi:10.1002/cite.330420912.
^Plimmer, R.H.A. (1912) [1908]. R.H.A. Plimmer; F.G. Hopkins (eds.).The Chemical Constitution of the Protein. Monographs on biochemistry. Vol. Part I. Analysis (2nd ed.). London: Longmans, Green and Co. p. 114. Retrieved3 June 2012.
^Singh, K. K.; Desai, Pinakin."Glutamate Chemical".TriveniInterChem.com. Riveni InterChem of Triveni Chemicals, manufacturer & supplier of industrial chemicals, India. Archived fromthe original on 2 July 2017. Retrieved11 August 2014.
^Desmo Exports Limited, Chemical Manufacturers and Importers of India (2011)."Monosodium Glutamate (MSG)".DesmoExports.com. Desmo Exports. Archived fromthe original on 11 June 2016. Retrieved11 August 2014.
^LeMesurier, Jennifer L. (8 February 2017)."Uptaking Race: Genre, MSG, and Chinese Dinner".Poroi.12 (2).doi:10.13008/2151-2957.1253.Introduction: 'Chinese Restaurant Syndrome' as Rhetorical [...] Finally, I trace how the journalistic uptakes of this discussion, in only taking up certain medical phrases and terms, reproduce the tacit racism of this boundary policing while avowing the neutrality of medical authority.
^Barry-Jester, Anna Maria (8 January 2016)."How MSG Got A Bad Rap: Flawed Science And Xenophobia".FiveThirtyEight.That MSG causes health problems may have thrived on racially charged biases from the outset. Ian Mosby, a food historian, wrote in a 2009 paper titled "'That Won-Ton Soup Headache': The Chinese Restaurant Syndrome, MSG and the Making of American Food, 1968-1980" that fear of MSG in Chinese food is part of the U.S.'s long history of viewing the "exotic" cuisine of Asia as dangerous or dirty.
^Blythman, Joanna (21 May 2018)."Chinese restaurant syndrome: has MSG been unfairly demonised?".The Guardian.Although Chang doesn't use MSG in his kitchens, he has defended its use, telling a high-level meeting of top chefs that Chinese restaurant syndrome is nothing more than a "cultural construct". That is a polite way of saying that avoidance of MSG is an expression of Western ignorance, or worse, racism, drawing on stereotypes of East Asian countries as dangerous or dirty.
^Geiling, Natasha (8 November 2013)."It's the Umami, Stupid. Why the Truth About MSG is So Easy to Swallow".Smithsonian.Everyone knows this connection, and probably associates MSG use in America most heavily with Chinese restaurants – thanks in large part to the absurdly racist name for MSG sensitivity "Chinese Restaurant Syndrome."
