Monosodium glutamate

This article is about the chemical compound. For its use in food, see glutamic acid (flavor). For glutamic acid in general, see glutamic acid.

Monosodium glutamate
IUPAC name Sodium 2-Aminopentanedioate
Identifiers
CAS number	142-47-2 Y
PubChem	85314
ChemSpider	76943 Y
UNII	C3C196L9FG Y
EC-number	205-538-1
Jmol-3D images	Image 1
SMILES [Na+].O=C([O-])[C@@H](N)CCC(=O)O
InChI InChI=1S/C5H9NO4.Na/c6-3(5(9)10)1-2-4(7)8;/h3H,1-2,6H2,(H,7,8)(H,9,10);/q;+1/p-1/t3-;/m0./s1 Y Key: LPUQAYUQRXPFSQ-DFWYDOINSA-M Y InChI=1/C5H9NO4.Na/c6-3(5(9)10)1-2-4(7)8;/h3H,1-2,6H2,(H,7,8)(H,9,10);/q;+1/p-1/t3-;/m0./s1 Key: LPUQAYUQRXPFSQ-SYBSRVMOBZ
Properties
Molecular formula	C5H8NNaO4
Molar mass	169.111 g/mol
Appearance	white crystalline powder
Melting point	232 °C, 505 K, 450 °F
Solubility in water	74g/100mL
Hazards
LD50	16600 mg/kg (oral, rat)
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Monosodium glutamate, also known as sodium glutamate or MSG, is the sodium salt of glutamic acid, one of the most abundant naturally occurring non-essential amino acids.^[1] It has been classified by the U.S. Food and Drug Administration as generally recognized as safe (GRAS) and by the European Union as a food additive. MSG has the HS code 29224220 and the E number E621.^[2] The glutamate of MSG confers the same umami taste of glutamate from other foods, being chemically identical.^[3] Industrial food manufacturers market and use MSG as a flavor enhancer because it balances, blends and rounds the total perception of other tastes.^[4][5] Trade names of monosodium glutamate include AJI-NO-MOTO®, Vetsin, and Ac'cent.

Invention

A Japanese chemist, Kikunae Ikeda, noticed that the Japanese broth of katsuobushi and kombu had a peculiar taste that could not be classified as sweet, salty, sour and bitter.^[6] In 1908, Ikeda extracted glutamic acid from the seaweed Laminaria japonica, kombu, and purified it by recrystallization. He named this new taste 'umami'.^[7] To verify that ionized glutamate was responsible for the umami taste, Ikeda studied the tastes 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.

Ikeda submitted a patent to produce this compound,^[8][6] and the Suzuki brothers started the commercial production of MSG in 1909 as AJI-NO-MOTO®, meaning the essence of taste in Japanese, the first time that monosodium glutamate was produced in the world.^[9][10][11]

Production and chemical properties

Since the first time that MSG was released into the market, it has been produced by three methods: (1) hydrolysis of vegetable proteins with hydrochloric acid to disrupt peptide bonds (1909 -1962), (2) direct chemical synthesis from acrylonitrile (1962 – 1973), and (3) 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. In order to meet the ever-increasing demand for MSG, 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.^[12]

Currently, most of the world production of MSG is by bacterial fermentation in a process similar to wine, vinegar, yogurt and even chocolate. 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.^[13] The yield and production rate from sugars to glutamate continues to improve in the industrial process, which allows manufacturers to keeping up with demand.^[11] The final product after filtration, concentration, acidification and crystallization is pure glutamate, sodium and water. It appears as a white and odorless crystalline powder that in solution dissociates into glutamate and sodium. It is freely soluble in water, but not hygroscopic and practically insoluble in common organic solvents such as ether.^[14]

In general, MSG is stable under the conditions of regular food processing. During cooking, MSG does not decompose, but like other amino acids, browning or Maillard reactions will occur in the presence of sugars at very high temperatures.^[9]

Usage

Pure MSG does not have a pleasant taste by itself if it is not combined with a consonant savory smell.^[15] As a flavor and in the right amount, MSG has the ability to enhance other taste-active compounds balancing and rounding the overall taste of certain dishes. MSG mixes well with meat, fish, poultry, many vegetables, sauces, soups and marinades, and increases the overall preference of certain foods like beef consommé.^[4] But like other basic tastes except sucrose, MSG improves the pleasantness only in the right concentration. An excess of MSG quickly ruins the taste of a dish. Although this 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.^[16] Moreover, there is an interaction between MSG and salt (sodium chloride) and other umami substances such as nucleotides. All need to be in an optimum concentration for maximum palatability. With these properties, MSG can be used to reduce salt intake (sodium), which predisposes to hypertension, heart diseases and stroke. The taste of low-salt foods improves with MSG even with a 30% salt reduction. The sodium content (in mass percent) of MSG is roughly one third (12%) as compared with sodium chloride (39%).^[17] Other salts of glutamate have been used in low-salt soups, but with a lower palatability than MSG.^[18]

Safety

MSG has been used for more than 100 years to season food. During this period, extensive studies were conducted to elucidate the role, benefits and 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 as the "Chinese restaurant syndrome" when anecdotally Robert Ho Man Kwok 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 never studied.^[20] With the years, the list of non specific symptoms has grown on anecdotal grounds. In normal conditions, we 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 rat and mice respectively, 5 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 Symptom complex was based on testimonial reports.^[21] This report also indicates that there is 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 that believed to react 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 that reported sensitivity to MSG. Multiple DBPC trials were performed and only subjects with at least two symptoms proceeded. Only 2 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] There have been several studies investigating 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

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., flavor enhancer), followed by either the name of the food additive, MSG, or its International Numbering System (INS) number, 621.^[32]

United States

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 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, which must be labeled with these common and usual names. 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 now used by the food industry when using glutamic acid (MSG without the sodium salt attached). Due to lack of FDA regulation, it is impossible to determine what percentage of 'natural flavor' is actually glutamic acid.

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 enthusiast and author Harold McGee states that "[after many studies], toxicologists have concluded that MSG is a harmless ingredient for most people, even in large amounts."^[33]

See also

• Acceptable daily intake
• Disodium glutamate
• Excitotoxicity
• List of food additives
• Monopotassium glutamate
• Umami

References

1. ^ Ninomiya K (1998). "Natural ocurrence". Food Reviews International 14 (2 & 3): 177–211. doi:10.1080/87559129809541157. 
2. ^ http://www.food.gov.uk/safereating/chemsafe/additivesbranch/enumberlist
3. ^ Ikeda K (November 2002). "New seasonings". Chem Senses 27 (9): 847–849. doi:10.1093/chemse/27.9.847. PMID 10736352. 
4. ^ ^{a b} Loliger J (April 2000). "Function and importance of Glutamate for Savory Foods". Journal of Nutrition 130 (4s Suppl): 915s – 920s. PMID 12438213. 
5. ^ Yamaguchi S (May 1991). "Basic properties of umami and effects on humans". Physiology & Behavior 49 (5): 833–841. doi:10.1016/0031-9384(91)90192-Q. PMID 1679557. 
6. ^ ^{a b} Ikeda K (November 2002). "New seasonings". Chem Senses 27 (9): 847–849. doi:10.1093/chemse/27.9.847. PMID 12438213. 
7. ^ Lindemann B, Ogiwara Y, Ninomiya Y (November 2002). "The discovery of umami". Chem Senses 27 (9): 843–844. doi:10.1093/chemse/27.9.843. PMID 12438211. 
8. ^ Ikeda K (1908). "A production method of seasoning mainly consists of salt of L-glutamic acid". Japanese Patent 14804. 
9. ^ ^{a b} Yamaguchi S, Ninomiya K (1998). "What is umami?". Food Reviews International 14 (2 & 3): 123–138. doi:10.1080/87559129809541155. 
10. ^ Kurihara K (September 2009). "Glutamate: from discovery as a food flavor to role as a basic taste (umami)?". The American Journal of Clinical Nutrition 90 (3): 719S–722S. doi:10.3945/ajcn.2009.27462D. PMID 19640953. 
11. ^ ^{a b c} Chiaki Sano (September 2009). "History of glutamate production". The American Journal of Clinical Nutrition 90 (3): 728S–732S. doi:10.3945/ajcn.2009.27462F. PMID 19640955. 
12. ^ Yoshida T (1970). "Industrial manufacture of optically active glutamic acid through total synthesis". Chem Ing Tech 42: 641–644. 
13. ^ Kinoshita S, Udaka S, Shimamoto M (1957). "Studies on amino acid fermentation. Part I. Production of L-glutamic acid by various microorganisms". J Gen Appl Microbiol 3: 193–205. 
14. ^ Win. C., ed (1995). Principles of Biochemistry. Boston, MA: Brown Pub Co.. 
15. ^ Rolls ET (September 2009). "Funtional neuroimaging of umami taste: what makes umami pleasant?". The American Journal of Clinical Nutrition 90 (3): 804S–813S. doi:10.3945/ajcn.2009.27462R. PMID 19571217. 
16. ^ Kawamura Y, Kare MR, ed (1987). Umami: a basic taste. New York, NY: Marcel Dekker Inc.. 
17. ^ Yamaguchi S, Takahashi C (January 1984). "Interactions of monosodium glutamate and sodium chloride on saltiness and palatability of a clear soup". Journal of Food Science 49 (1): 82–85. doi:10.1111/j.1365-2621.1984.tb13675.x. 
18. ^ Ball P, Woodward D, Beard T, Shoobridge A, Ferrier M (June 2002). "Calcium diglutamate improves taste characteristics of lower-salt soup". Eur J Clin Nutr 56 (6): 519–523. doi:10.1038/sj.ejcn.1601343. PMID 12032651. 
19. ^ ^{a b} Walker R, Lupien JR (April 2000). "The safety evaluation of monosodium glutamate". Journal of Nutrition 130 (4S Suppl): 1049S–1052S. PMID 10736380. 
20. ^ ^{a b} Freeman, M (2006). "Reconsidering the effects of monosodium glutamate: A literature review". Journal of the American Academy of Nurse Practicioners 18 (10): 482–486. doi:10.1111/j.1745-7599.2006.00160.x. PMID 16999713. 
21. ^ Raiten DJ, Talbot JM, Fisher KD (1996). "Executive Summary from the Report: Analysis of Adverse Reactions to Monosodium Glutamate (MSG)". Journal of Nutrition 126 (6): 1743–1745. PMID 7472671. 
22. ^ Geha RS, Beiser A, Ren C et al. (April 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. http://jn.nutrition.org/cgi/pmidlookup?view=long&pmid=10736382. 
23. ^ ^{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. 
24. ^ Freeman M. (October 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. 
25. ^ Walker R (October 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. 
26. ^ Willams, A. N., and Woessner, K.M. (2009). "Monosodium glutamate 'allergy': menace or myth?". Clinical & Experimental Allergy 39 (5): 640–646. doi:10.1111/j.1365-2222.2009.03221.x. 
27. ^ Shi, Z; Luscombe-Marsh, ND; Wittert, GA; Yuan, B; Dai, Y; Pan, X; Taylor, AW (2010). "Monosodium glutamate is not associated with obesity or a greater prevalence of weight gain over 5 years: Findings from the Jiangsu Nutrition Study of Chinese adults". The British journal of nutrition 104 (3): 457–63. doi:10.1017/S0007114510000760. PMID 20370941. 
28. ^ Nicholas bakalar (August 25, 2008). "Nutrition: MSG Use Is Linked to Obesity". The New York Times. http://www.nytimes.com/2008/08/26/health/nutrition/26nutr.html. Retrieved 2010-11-10. "Consumption of monosodium glutamate, or MSG, the widely used food additive, may increase the likelihood of being overweight, a new study says." 
29. ^ Stevenson, D. D. (2000). "Monosodium glutamate and asthma". J. Nutr. 130 (4S Suppl): 1067S–1073S. PMID 10736384. 
30. ^ Nicholas J. Maragakis, MD; Jeffrey D. Rothstein, MD, PhD (2001;58:365-370.). "Glutamate Transporters in Neurologic Disease". Neurology. http://archneur.ama-assn.org/cgi/content/extract/58/3/365?maxtoshow=&hits=10&RESULTFORMAT=&fulltext=monosodium+glutamate&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT. Retrieved 2010-11-10. "Glutamate is the primary excitatory amino acid neurotransmitter in the human brain. It is important in synaptic plasticity, learning, and development. Its activity at the synaptic cleft is carefully balanced by receptor inactivation and glutamate reuptake. When this balance is upset, excess glutamate can itself become neurotoxic. ... This overactivation leads to an enzymatic cascade of events ultimately resulting in cell death." 
31. ^ "MSG In Food". Food Standards Code. Food Standards Australia New Zealand. http://www.foodstandards.gov.au/scienceandeducation/factsheets/factsheets2008/msginfood.cfm. Retrieved May 17, 2010. 
32. ^ "Standard 1.2.4 Labelling of Ingredients". Food Standards Code. Food Standards Australia New Zealand. http://www.foodstandards.gov.au/foodstandards/foodstandardscode/standard124labelling4231.cfm. Retrieved May 15, 2010. 
33. ^ curiouscook.com McGee, Harold, On Food and Cooking, the Science and Lore of the Kitchen, 2004

External links

• Monosodium glutamate: Is it harmful? (Mayo Clinic)
• The Facts on Monosodium Glutamate (EUFIC)