Monosodium glutamate

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This article is about the chemical compound. For its use in food, see glutamic acid (flavor). For glutamic acid in general, see glutamic acid.
For other uses, see MSG (disambiguation).
Monosodium glutamate
Chemical composition of monosodium glutamate
Structure of monosodium glutamate
Crystalline monosodium glutamate
Identifiers
CAS number 142-47-2 YesY
PubChem 85314
ChemSpider 76943 YesY
UNII C3C196L9FG YesY
EC-number 205-538-1
Jmol-3D images Image 1
Properties
Molecular formula C5H8NO4Na
Molar mass 169.111 g/mol
Appearance White crystalline powder
Melting point 232 °C (450 °F; 505 K)
Solubility in water 74 g/100 mL[1]
Hazards
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
LD50 16600 mg/kg (oral, rat)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Monosodium glutamate (MSG), also known as sodium glutamate, is the sodium salt of glutamic acid, one of the most abundant naturally occurring non-essential amino acids.[2]

MSG was classified by the U.S. Food and Drug Administration as generally recognized as safe (GRAS)[3] and by the European Union as a food additive. MSG has the HS code 29224220 and the E number E621.[4]

The L-glutamate form of MSG confers the same umami taste of free L-glutamate naturally found in foods.[5] Industrial food manufacturers market and use MSG as a flavor enhancer because it balances, blends and rounds the total perception of other tastes.[6][7] Trade names of monosodium glutamate include Ac'cent, Aji-No-Moto, and Ve-Tsin.

History[edit]

Flavor enhancers containing MSG have been used since antiquity. Garum, a fish sauce produced by fermentation, was widely used by the Romans to season their food and contained monosodium glutamate as a byproduct of the fermentation process.[8]

Kikunae Ikeda from the Tokyo Imperial University isolated glutamic acid as a new taste substance in 1908 from the seaweed Laminaria japonica, kombu, by aqueous extraction and crystallization, and named its taste "umami".[9] He noticed that dashi, the Japanese broth of katsuobushi and kombu, had a peculiar taste that had not been scientifically described at that time and differed from sweet, salty, sour and bitter.[9] To verify that ionized glutamate was responsible for the umami taste, Professor Ikeda studied the taste properties of many glutamate salts such as calcium, potassium, ammonium, and magnesium glutamate. All salts elicited umami in addition to a certain metallic taste due to the other minerals. Among those salts, sodium glutamate was the most soluble and palatable, and crystallized easily.

Professor Ikeda named this product monosodium glutamate and submitted a patent to produce MSG.[10] Suzuki brothers started the first commercial production of MSG in 1909 as Aji-no-moto, meaning "essence of taste" in English.[11][12][13]

Usage[edit]

Pure MSG is not reported to have a highly pleasant taste until it is combined with a savoury odor. [14] The basic sensory function of MSG is attributed to its ability to enhance the presence of savoury taste-active compounds when included at the right concentration.[6]

The optimum concentration varies with the type of food; in clear soup, the pleasantness score rapidly falls with more than 1 g of MSG per 100 ml.[15] There is also an interaction between MSG and salt (sodium chloride), and other umami substances such as nucleotides.

With these properties, MSG can be used to reduce salt intake (sodium), which predisposes to hypertension, heart diseases and stroke.[16] By adding MSG appropriately, salt can be reduced by 30 to 40 percent without a perceived reduction in saltiness.[6]

The sodium content (in mass percent) of MSG is roughly a third of the amount (12%) than in sodium chloride (39%).[17] Other salts of glutamate have been used in low-salt soups, but with a lower palatability than MSG.[18]

Safety[edit]

MSG has been used for more than 100 years to season food. During this period, many studies have been conducted on the safety of MSG. At this point, international and national bodies for the safety of food additives consider MSG safe for human consumption as a flavor enhancer.[19] The "MSG symptom complex" was originally termed the "Chinese Restaurant Syndrome" when Robert Ho Man Kwok anecdotally reported the symptoms he felt after an American-Chinese meal. Kwok suggested multiple reasons behind the symptoms, including alcohol from cooking with wine, the sodium content, or the MSG seasoning. But MSG became the focus and the symptoms have been associated with MSG ever since. The effect of wine or salt content was not studied.[20] With the years, the list of non-specific symptoms has grown on anecdotal grounds. In normal conditions, humans have the ability to metabolize glutamate that has a very low acute toxicity. The oral lethal dose to 50% of subjects (LD50) is between 15 to 18 g/kg body weight in rats and mice respectively, five times greater than the LD50 of salt (3 g/kg in rats). Therefore, the intake of MSG as a food additive and the natural level of glutamic acid in foods do not represent a toxicological concern in humans.[19]

A report from the Federation of American Societies for Experimental Biology (FASEB) compiled in 1995 on behalf of the United States Food and Drug Administration (FDA) concluded that MSG is safe when "eaten at customary levels" and although there seems to be a subgroup of apparently healthy individuals that respond with the MSG symptom complex when exposed to 3 g of MSG in the absence of food, causality by MSG has not been established because the list of MSG symptoms was based on testimonial reports.[21]

This report also indicates that there are no data to support the role of glutamate in chronic and debilitating illnesses. A controlled double-blind multicenter clinical trial failed to demonstrate the relationship between MSG symptom complex and the consumption of MSG in individuals who believed they reacted adversely against MSG. No statistical association has been demonstrated, there were few responses and they were inconsistent. Symptoms were not observed when MSG was given with food.[22][23][24][25]

Adequately controlling for experimental bias includes a double-blind placebo-controlled experimental design (DBPC) and the application in capsules because of the strong and unique after-taste of glutamates.[23] In a study performed by Tarasoff and Kelly (1993) 71 fasting participants were given 5 g of MSG and then administered a standard breakfast. There was only one reaction, and it was to the placebo in a self-identified MSG-sensitive individual.[20] In a different study done by Geha et al. (2000), they tested the reaction of 130 subjects who reported sensitivity to MSG. Multiple DBPC trials were performed and only subjects with at least two symptoms proceeded. Only two people out of the whole study responded in all four challenges. Because of this low prevalence, the researchers concluded that the response to MSG was not reproducible.[26]

Additional studies that have looked into whether MSG causes obesity have given mixed results.[27][28] Several studies have investigated an anecdotal link between MSG and asthma; current evidence does not support any causal association.[29]

Since glutamates are important neurotransmitters in the human brain, playing a key element in learning and memory, there is ongoing study by neurologists about possible side-effects of MSG in food but no conclusive studies drawing any connections.[30]

Australia and New Zealand[edit]

Food Standards Australia New Zealand[31] (FSANZ) cites "overwhelming evidence from a large number of scientific studies" to explicitly deny any link between MSG and "serious adverse reactions" or "long-lasting effects", declaring MSG "safe for the general population". It does, however, describe that in less than 1% of the population, sensitive individuals may experience "transient" side effects such as "headache, numbness/tingling, flushing, muscle tightness, and generalised weakness" to a large amount of MSG taken in a single meal. People who consider themselves sensitive to MSG are encouraged to confirm this through an appropriate clinical assessment.

Standard 1.2.4 of the Australia and New Zealand Food Standards Code requires the presence of MSG as a food additive to be labeled in packaged foods. The label must bear the food additive class name (e.g., flavour enhancer), followed by either the name of the food additive, MSG or its International Numbering System (INS) number, 621.[32]

United States[edit]

Monosodium glutamate (MSG) is one of several forms of glutamic acid found in foods, in large part because glutamic acid, being an amino acid, is pervasive in nature. Glutamic acid and its salts can be present in a wide variety of other additives, including hydrolyzed vegetable protein, autolyzed yeast, hydrolyzed yeast, yeast extract, soy extracts, and protein isolate, which must be labeled with these specialized names even though they are unfamiliar to the general public. Since 1998, MSG cannot be included in the term "spices and flavorings". The food additives disodium inosinate and disodium guanylate, which are ribonucleotides, are usually used in synergy with monosodium glutamate-containing ingredients. However, the term "natural flavor" is used by the food industry when using glutamic acid (which is similar to MSG, lacking only the sodium ion). The FDA does not require disclosure of the specific components and amounts used in "natural flavor." [33]

The FDA considers labels such as "No MSG" or "No Added MSG" to be misleading if the food contains ingredients that are sources of free glutamate, such as hydrolyzed protein. In 1993, the FDA proposed adding the phrase "contains glutamate" to the common or usual names of certain protein hydrolysates that contain substantial amounts of glutamate.[citation needed]

Production[edit]

Since MSG was released into the market, it 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.[11]

Initially, wheat gluten was used for hydrolysis because it contains more than 30 g of glutamate and glutamine in 100 g of protein. But as the production to achieve the ever-increasing demand for MSG augmented, new production processes were studied: chemical synthesis and fermentation.

The polyacrylic fiber industry began in Japan in the mid-1950s and acrylonitrile was adopted then as starting material to synthesize MSG.[34]

Currently, most of the world production of MSG is by bacterial fermentation in a process similar to vinegar or yogurt. Sodium is added later through the steps of neutralization. During fermentation, selected bacteria (coryneform bacteria) cultured with ammonia and carbohydrates from sugar beets, sugar cane, tapioca or molasses, excrete amino acids into the culture broth from where L-glutamate is isolated. Kyowa Hakko Kogyo Co Ltd developed the first industrial fermentation to produce L-glutamate.[35]

The conversion yield and production rate from sugars to glutamate continues to improve in the industrial production of MSG, keeping up with increasing demand.[11] The final product after filtration, concentration, acidification and crystallization is pure glutamate, sodium and water. It appears as a white, odorless crystalline powder that in solution dissociates into glutamate and sodium ions.

Chemical properties[edit]

MSG is freely soluble in water but not hygroscopic and practically insoluble in common organic solvents such as ether.[36]

In general, MSG is stable under the conditions of regular food processing. During cooking, MSG does not decompose: Like other amino acids, browning or Maillard reactions will occur in the presence of sugars at very high temperatures.[12]

See also[edit]

References[edit]

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External links[edit]