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Monosodium glutamate

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This article is about the chemical compound. For its use in food flavouring and health concerns, see glutamic acid (flavor). For glutamic acid in general, see glutamic acid.
Monosodium glutamate
Names
IUPAC name
Sodium (2S)-2-amino-5-hydroxy-5-oxo-pentanoate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.005.035 Edit this at Wikidata
E number E621 (flavour enhancer)
  • C(CC(=O)O)C(C(=O)[O-])N.[Na+]
Properties
C5H8NNaO4
Molar mass 169.111 g/mol
Appearance white crystalline powder
Melting point 225 °C (437 °F; 498 K)
74g/100mL
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Crystalline monosodium glutamate

Monosodium glutamate, also known as sodium glutamate and MSG, is a sodium salt of the non-essential amino acid glutamic acid. It is used as a food additive and is commonly marketed as a flavour enhancer. It has the HS code 29224220 and the E number E621. Trade names of monosodium glutamate include Ajinomoto, Vetsin, and Accent. It was once predominantly made from wheat gluten, but is now mostly made from bacterial fermentation; it is acceptable for celiacs following a gluten-free diet.[1][2][3][4]

Although traditional Asian cuisine had often used seaweed extract, which contains high concentrations of glutamic acid, MSG was not isolated until 1907 by Kikunae Ikeda. MSG was subsequently patented by Ajinomoto Corporation of Japan in 1909. In its pure form, it appears as a white crystalline powder; when immersed in water or saliva, it rapidly dissociates into sodium cations and glutamate anions (glutamate is the anionic form of glutamic acid, a naturally occurring amino acid).

Production and chemical properties

MSG is normally obtained by the fermentation of carbohydrates, using bacterial or yeast species from genera such as Brevibacterium, Arthrobacter, Microbacterium, and Corynebacterium. Yields of 100 g/litre [citation needed] can be prepared in this way. From 1909 to the mid 1960s, MSG was prepared by the hydrolysis of wheat gluten, which is roughly 25% glutamic acid. Glutamic acid is one of the least soluble amino acids, which facilitates its purification.[5]

Like the sodium salts of other amino acids, MSG is a stable colourless solid that is degraded by strong oxidizing agents. It exists as a pair of mirror image stereoisomers (enantiomers), but only the naturally occurring L-glutamate form is used as a flavour enhancer.

Commercialization

The Ajinomoto company was formed to manufacture and market MSG in Japan; the name 'Aji no moto' translates to "essence of taste". It was introduced to the United States in 1947 as Ac'cent flavor enhancer.[6]

Modern commercial MSG is produced by fermentation[7] of starch, sugar beets, sugar cane, or molasses. About 1.5 million tonnes were sold in 2001, with 4% annual growth expected.[8] MSG is used commercially as a flavour enhancer. Although once associated with foods in Chinese restaurants, MSG is now used by most fast food chains and in many foodstuffs, particularly processed foods.[9]

Examples include:

Only the L-glutamate enantiomer has flavour-enhancing properties.[10] Manufactured MSG contains over 99.6% of the naturally predominant L-glutamate form, which is a higher proportion of L-glutamate than found in the free glutamate ions of naturally occurring foods. Fermented products such as soy sauce, steak sauce, and Worcestershire sauce have levels of glutamate similar to foods with added MSG. However, glutamate in these brewed products may have 5% or more of the D-enantiomer.[10]

Health concerns

Main article: Glutamic acid (flavor) § Research into health effects

MSG as a food ingredient has been the subject of health studies. A report from the Federation of American Societies for Experimental Biology (FASEB) compiled in 1995 on behalf of the FDA concluded that MSG was safe for most people when "eaten at customary levels." However, it also said that, based on anecdotal reports, some people may have an MSG intolerance which causes "MSG symptom complex" — commonly referred to as Chinese restaurant syndrome — and/or a worsening of asthmatic symptoms.[11] Subsequent research found that while large doses of MSG given without food may elicit more symptoms than a placebo in individuals who believe that they react adversely to MSG, the frequency of the responses was low and the responses reported were inconsistent, not reproducible, and were not observed when MSG was given with food.[12] While many people believe that MSG is the cause of these symptoms, a statistical association has not been demonstrated under controlled conditions, even in studies with people who were convinced that they were sensitive to it.[12][13][14][15] Adequately controlling for experimental bias includes a placebo-controlled double-blinded experimental design and the application in capsules because of the strong and unique after-taste of glutamates.[13]

Obesity

In 2008, researchers at the University of North Carolina at Chapel Hill, working with Chinese researchers, published a study that found a positive link between MSG intake and obesity in humans: Prevalence of overweight was significantly higher in MSG users than in non-users. The population in this study was 752 healthy rural Chinese villagers between the ages of 40 and 59, of whom 48.7% were women.[16][17] [18]

Previously, monosodium glutamate has been shown to indirectly cause obesity in lab rats by downregulating hypothalamic appetite suppression and, thus, increasing the amount of food the lab rats consumed. However, at least one study (1978) found that this obesity effect (widely used in obesity research using rats and mice, and also observed in Chinese hamsters) was not dependent on additional food intake.[19] Animal research demonstrating an inverse relationship between increased glutamate intake via maternal feeding and serum levels of growth hormone, combined with an epidemiological survey of 2,239,960 German adults demonstrating an inverse relationship between height and morbid obesity, compels some researchers to theorize (2006) that monosodium glutamate has a role in the occurrence of obesity in humans.[20] In contrast, a 2008 Japanese study sponsored by a MSG manufacturer found that that rats lost body fat when fed MSG ad lib.[21]

However, an earlier study (1973) did not find a similar effect in humans. The epidemiological survey of 4,938 ethnically Japanese men drawn from the Honolulu heart program in Hawaii found that self-reported dietary monosodium glutamate consumption was not statistically linked with obesity.[22][23] Researchers furthermore found that frequent monosodium glutamate consumption did not significantly affect blood sugar or serum cholesterol levels among the participants.

Monosodium glutamate may worsen non-alcoholic fatty liver disease caused by trans fats.[24]

A rat study conducted by the Institute of Life Sciences in Kawasaki, Japan during which the experimental rats were allowed to freely drink a solution of MSG and water showed a reduction in abdominal fat and weight gain compared to control rats.[25]

United States

Monosodium glutamate is one of several forms of glutamic acid found in foods, in large part because glutamic acid is pervasive in nature, being an amino acid. Glutamic acid and its salts can also be present in a wide variety of other additives, including hydrolyzed vegetable proteins, autolyzed yeast, hydrolyzed yeast, yeast extract, soy extracts, and protein isolate, any one of which may appear as "spices" or "natural flavorings." The food additives disodium inosinate and disodium guanylate are usually used along with monosodium glutamate-containing ingredients, and provide a likely indicator of the presence of monosodium glutamate in a product. For this reason, 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.

In the 2004 version of his book, On Food and Cooking, food scientist Harold McGee states that "[after many studies], toxicologists have concluded that MSG is a harmless ingredient for most people, even in large amounts."

Asia

The INTERMAP Cooperative Research Group conducted a study of 752 healthy Chinese (48.7% women), age 40–59 years, randomly sampled from three rural villages in north and south China and determined that MSG intake may be positively correlated to an increased BMI (Body Mass Index).[26]

Australia and New Zealand

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. 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.

See also

References

  1. ^ http://www.celiac.com/articles/181/1/Safe-Gluten-Free-Food-List-Safe-Ingredients/Page1.html
  2. ^ Leung, Albert Y. (2003). "Monosodium Glutamate". Encyclopedia of Common Natural Ingredients: Used in Food, Drugs, and Cosmetics (2nd ed.). New York: Wiley. pp. 373–375. ISBN 978-0-471-47128-8. Monosodium glutamate can generally be produced by three methods: (1) hydrolysis of proteins such as gluten or proteins present in sugar beet wastes, (2) synthesis, and (3) microbial fermentation. In the hydrolysis method, the protein is hydrolyzed with a strong mineral acid to free amino acids, and the glutamic acid is then separated from the mixture, purified, and converted to its monosodium salt, [monosodium glutamate]. This used to be the major method of [monosodium glutamate] manufacture. Currently most of the world production of [monosodium glutamate] is by bacterial fermentation. In this method bacteria (especially strains of Micrococcus glutamicus) are grown aerobically in a liquid nutrient medium containing a carbon source (e.g., dextrose or citrate), a nitrogen source such as ammonium ions or urea, and mineral ions and growth factors. The bacteria selected for this process have the ability to excrete glutamic acid they synthesize outside of their cell membrane into the medium and accumulate there. The glutamic acid is separated from the fermentation broth by filtration, concentration, acidification, and crystallization, followed by conversion to its monosodium salt [monosodium glutamate]. {{cite encyclopedia}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  3. ^ http://www.celiac.ca/Articles/Fall1990-1.html
  4. ^ http://www.jstor.org/stable/3421360
  5. ^ Kawakita, Tetsuya (2005). "Monosodium Glutamate". Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a16 711. {{cite encyclopedia}}: Check |doi= value (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ Sand, Jordan (2005). "A Short History of MSG". Gastronomica. 5 (4): pp. 38–49. doi:10.1525/gfc.2005.5.4.38. {{cite journal}}: |pages= has extra text (help)
  7. ^ "Production process". Encyclopedia of Amino Acids. Anjimoto Co., Inc.
  8. ^ http://www.ajinomoto.co.jp/ajinomoto/A-Company/company/zaimu/pdf/fact/food_biz.pdf
  9. ^ Moskin, Julia (2008-03-05). "Yes, MSG, the Secret Behind the Savor". New York Times.
  10. ^ a b Rundlett, Kimber L (1994). "Evaluation of free D-glutamate in processed foods". Chirality. 6 (4): pp. 277–282. doi:10.1002/chir.530060410. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  11. ^ http://vm.cfsan.fda.gov/~lrd/msg.html
  12. ^ a b Geha RS, Beiser A, Ren C; et al. (2000). "Review of alleged reaction to monosodium glutamate and outcome of a multicenter double-blind placebo-controlled study". J. Nutr. 130 (4S Suppl): 1058S – 62S. PMID 10736382. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  13. ^ a b Tarasoff L., Kelly M.F. (1993). "Monosodium L-glutamate: a double-blind study and review". Food Chem. Toxicol. 31 (12): 1019–1035. doi:10.1016/0278-6915(93)90012-N. PMID 8282275.
  14. ^ Freeman M. (2006). "Reconsidering the effects of monosodium glutamate: a literature review". J Am Acad Nurse Pract. 18 (10): 482–6. doi:10.1111/j.1745-7599.2006.00160.x. PMID 16999713. {{cite journal}}: Unknown parameter |month= ignored (help)
  15. ^ Walker R (1999). "The significance of excursions above the ADI. Case study: monosodium glutamate". Regul. Toxicol. Pharmacol. 30 (2 Pt 2): S119 – S121. doi:10.1006/rtph.1999.1337. PMID 10597625. {{cite journal}}: Unknown parameter |month= ignored (help)
  16. ^ http://uncnews.unc.edu/content/view/1465/71/
  17. ^ http://www.nature.com/oby/journal/v16/n8/full/oby2008274a.html
  18. ^ He, Ka, et al., "Association of Monosodium Glutamate Intake with Overweight in Chinese Adults: The INTERMAP Study," Obesity (2008) 16, 1875-1880.
  19. ^ Poon TK, Cameron DP (1978). "Measurement of oxygen consumption and locomotor activity in monosodium glutamate-induced obesity". Am J Physiol. 234 (5): E532–4. PMID 645905.
  20. ^ Hermanussen M, Garcia AP, Sunder M, Voigt M, Salazar V, Tresguerres JA. (2006). "Obesity, voracity, and short stature: the impact of glutamate on the regulation of appetite". Eur J Clin Nutr. 60 (1): 25–31. doi:10.1038/sj.ejcn.1602263. PMID 16132059.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  21. ^ Kondoh T, Torii K (2008). "MSG intake suppresses weight gain, fat deposition, and plasma leptin levels in male Sprague-Dawley rats". Physiol. Behav. 95 (1–2): 135–44. doi:10.1016/j.physbeh.2008.05.010. PMID 18559279. {{cite journal}}: Unknown parameter |month= ignored (help)
  22. ^ Go G, Nakamura FH, Rhoads GG, Dickinson LE. (1973). "Long-term health effects of dietary monosodium glutamate". Hawaii Med J. 32 (1): 13–7. PMID 4689313.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. ^ Honolulu Heart Program
  24. ^ Collison KS, Maqbool Z, Saleh SM; et al. (2009). "Effect of dietary monosodium glutamate on trans fat-induced nonalcoholic fatty liver disease". Journal of Lipid Research. 50 (8): 1521–1537. PMID 19001666. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  25. ^ Kondoh T, Torii K (2008-05-16). "MSG intake suppresses weight gain, fat deposition, and plasma leptin levels in male Sprague-Dawley rats". Physiol Behav. PMID 18559279.
  26. ^ He, Ka (2008). "Association of monosodium glutamate intake with overweight in Chinese adults: the INTERMAP Study". Obesity. 16 (8). The Obesity Society: pp. 1875–1880. doi:10.1038/oby.2008.274. PMID 18497735. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
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