Monosodium glutamate

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This article is about monosodium glutamate as a food additive. For an overview of the chemistry of glutamic acid, see glutamic acid.
Chemical structure of monosodium glutamate

Monosodium glutamate, sodium glutamate, flavour enhancer 621, EU food additive code: E621, HS code: 29224220 (IUPAC name: 2-aminopentanedioic acid. Also known as :2-aminoglutaric acid), commonly known as MSG, Ajinomoto or Vetsin, is a sodium salt of glutamic acid. MSG is a food additive, popularly marketed as a "flavour enhancer".

Crystalline MSG

It was discovered and patented in 1909 by Ajinomoto Corporation in Japan. In its pure form, it appears as a white crystalline powder; when dissolved in water (or saliva) it rapidly dissociates into free sodium and glutamate ions (glutamate is the anionic form of glutamic acid, a naturally occurring amino acid).

Umami

MSG stimulates specific receptors located in taste buds such as the amino acid receptor T1R1/T1R3 or other glutamate receptors like the metabotropic receptors (mGluR4 and mGluR1) which induce the taste known as umami, one of the five basic tastes (the word umami is a loanword from Japanese; it is also referred to as "savory" or "meaty").


Discovery

Although they are naturally occurring in many foods, the flavour contributions made by glutamate and other amino acids were only scientifically identified early in the twentieth century. In 1907, Japanese researcher Kikunae Ikeda of the Tokyo Imperial University identified brown crystals left behind after the evaporation of a large amount of kombu broth as glutamic acid. These crystals, when tasted, reproduced the ineffable but undeniable flavour he detected in many foods, most especially in seaweed. Professor Ikeda termed this flavour "umami." He then patented a method of mass-producing a crystalline form of glutamic acid, MSG.[1]

Commercialization

Template:Globalize/USA

The Ajinomoto (味の素) company was formed to manufacture and market MSG in Japan; the name 'Ajinomoto' means "essence of taste". It was introduced to the United States in 1947 as Ac'cent flavor enhancer.

Modern commercial MSG is produced by fermentation[2] of starch, sugar beets, sugar cane, or molasses. About 1.5 million metric tons were sold in 2001, with 4% annual growth expected.[3] MSG is used commercially as a flavour enhancer. Once stereotypically associated with food in Chinese restaurants, it is now more often found in many of the most common food products consumed in the US:

  • most canned soups of the US food industry like Campbell's (except the low sodium varieties)
  • most beef and chicken stocks of the US food industry like Swansons (except the low sodium varieties)
  • most flavored potato chip products of the US food industry
  • many other snack foods
  • many frozen dinners
  • almost all US-originated fast foods
  • instant meals such as the seasoning mixtures for instant noodles.

Health

In 1959, the FDA classified MSG as a "generally recognized as safe", or GRAS, substance. This action stemmed from the 1958 Food Additives Amendment to the Federal Food, Drug, and Cosmetic Act, which required premarket approval for new food additives and led the FDA to promulgate regulations listing substances, such as MSG, which have a history of safe use or are otherwise GRAS. Since 1970, FDA has sponsored extensive reviews on the safety of MSG, other glutamates and hydrolyzed proteins, as part of an ongoing review of safety data on GRAS substances used in processed foods. One such review was by the Federation of American Societies for Experimental Biology (FASEB) Select Committee on GRAS Substances. In 1980, the committee concluded that MSG was safe at current levels of use but recommended additional evaluation to determine MSG's safety at significantly higher levels of consumption. Additional reports attempted to look at this. In 1986, FDA's Advisory Committee on Hypersensitivity to Food Constituents concluded that MSG poses no threat to the general public but that reactions of brief duration might occur in some people. Other reports have given the following findings:

  • A 1991 report by the European Community's (EC) Scientific Committee for Foods reaffirmed MSG's safety and classified its "acceptable daily intake" as "not specified", the most favorable designation for a food ingredient. In addition, the EC Committee said, "Infants, including prematures, have been shown to metabolize glutamate as efficiently as adults and therefore do not display any special susceptibility to elevated oral intakes of glutamate."
  • A 1992 report from the Council on Scientific Affairs of the American Medical Association stated that glutamate in any form has not been shown to be a "significant health hazard".
  • A 1995 FDA-commissioned report acknowledged that "An unknown percentage of the population may react to MSG and develop MSG symptom complex, a condition characterized by one or more of the following symptoms:
    • burning sensation in the back of the neck, forearms and chest
    • numbness in the back of the neck, radiating to the arms and back
    • tingling, warmth and weakness in the face, temples, upper back, neck and arms
    • facial pressure or tightness
    • chest pain
    • headache
    • nausea
    • rapid heartbeat
    • bronchospasm (difficulty breathing) in MSG-intolerant people with asthma
    • drowsiness
    • weakness."[4]

Issues surrounding these health implications of MSG consumption are the subject of much debate. A considerable body of anecdotal evidence exists suggesting negative health effects, but this has not yet been supported by recognised research.

In April 1968 Dr Ho Man Kwok wrote an article for the New England Journal of Medicine where he said, "I have experienced a strange syndrome whenever I have eaten out in a Chinese restaurant, especially one that served northern Chinese food. The syndrome, which usually begins 15 to 20 minutes after I have eaten the first dish, lasts for about two hours, without hangover effect. The most prominent symptoms are numbness at the back of the neck, gradually radiating to both arms and the back, general weakness and palpitations...". This comment began a global health scare about MSG and "Chinese restaurant syndrome" was born. Considerable research has failed to find any syndrome related to MSG (or in fact any negative health effects at all), and Chinese restaurant syndrome is largely resigned to myth status. However, the damage was done, and MSG is still thought of as suspect by a large proportion of the general public, and many foods continue to be labelled "MSG free". [5]

Excitotoxicity

Because MSG is absorbed very quickly (unlike glutamic acid-containing proteins in foods), MSG could spike blood plasma levels of glutamate.[6][7][8] Glutamic acid is in a class of chemicals known as excitotoxins, high levels of which have been shown in animal studies to cause damage to areas of the brain unprotected by the blood-brain barrier and that a variety of chronic diseases can arise out of this neurotoxicity.[9][10] The debate among scientists on the significance of these findings has been raging since the early 1970s, when Dr. John Olney found that high levels of glutamic acid caused damage to the brains of infant mice.[11] The debate is complex and has focused on several areas:

  • Whether the increase in plasma glutamate levels from typical ingestion levels of MSG is enough to cause neurotoxicity in one dose or over time.
  • Whether humans are susceptible to the neurotoxicity from glutamic acid seen in some animal experiments. It is known that the glutamate ion is important in memory retrieval in humans.
  • Whether neurotoxicity from excitotoxins is caused by the combined effect of glutamic acid and other excitotoxins such as aspartic acid from aspartame.

At a meeting of the Society for Neuroscience, the delegates had a split opinion on the issues related to neurotoxic effects from excitotoxic amino acids found in some additives such as MSG.[12]

Some scientists believe that humans and other primates are not as susceptible to excitotoxins as rodents and therefore there is little concern with glutamic acid from MSG.[13][14] While they agree that the combined effects of all food-based excitotoxins should be considered,[15] their measurements of the blood plasma levels of glutamic acid after ingestion of monosodium glutamate and aspartame demonstrate that there is not a cause for concern.[16] Other scientists feel that primates are susceptible to excitotoxic damage[17] and that humans concentrate excitotoxins in the blood more than other animals.[18] Based on these findings, they feel that humans are approximately 5-6 times more susceptible to the effects of excitotoxins than rodents are.[19] While they agree that typical use of MSG does not spike glutamic acid to extremely high levels in adults, they are particularly concerned with potential effects in infants and young children[20] and the potential long-term neurodegenerative effects of small-to-moderate spikes on plasma excitotoxin levels.[21]

In animals

Monosodium Glutamate (MSG) has been shown to cause obesity in lab rats (PMID 16132059).

Ingredient listing

United States

Under current FDA regulations, when MSG is added to a food, it must be identified as "monosodium glutamate" in the label's ingredient list. Each ingredient used to make a food must be declared by its name in this list.

While technically MSG is only one of several forms of free glutamate used in foods, consumers frequently use the term MSG to mean all free glutamate. The free glutamic acid component of MSG may also be present in a wide variety of other additives, including hydrolyzed vegetable proteins, hydrolyzed yeast, soy extracts, and "natural flavorings".

For this reason, FDA considers labels such as "No MSG" or "No Added MSG" to be misleading if the food contains ingredients that are sources of free glutamates, such as hydrolyzed protein.

In 1993, FDA proposed adding the phrase "(contains glutamate)" to the common or usual names of certain protein hydrolysates that contain substantial amounts of glutamate. For example, if the proposal were adopted, hydrolyzed soy protein would have to be declared on food labels as "hydrolyzed soy protein (contains glutamate)." However, if FDA issues a new proposal, it would probably supersede this 1993 one.

In 1994, FDA received a citizen's petition requesting changes in labeling requirements for foods that contain MSG or related substances. The petition asks for mandatory listing of MSG as an ingredient on labels of manufactured and processed foods that contain manufactured free glutamic acid. It further asks that the amount of free glutamic acid or MSG in such products be stated on the label, along with a warning that MSG may be harmful to certain groups of people. FDA has not yet taken action on the petition.

Under current FDA regulations, significant amounts of free glutamate can be included in food under the following ingredient labels: MSG, monosodium glutamate, glutamic acid, hydrolyzed protein, autolyzed protein, textured protein, yeast extract, autolyzed yeast extract, protein isolate, soy sauce, modified food starch, modified corn starch, calcium caseinate, and sodium caseinate. In some cases, significant amounts of free glutamate are also added as broth, maltodextrin, seasonings, or natural flavor. [1] [2] [3]

Australia and New Zealand

Standard 1.2.4 of the Australia New Zealand Food Standards Code requires the presence of MSG as a food additive to be labelled. The label must bear the food additive class name (eg. flavour enhancer), followed by either the name of the food additive (eg MSG) or its International Numbering System (INS) number (eg 621).

References

  • Jordan Sand, "A Short History of MSG: Good Science, Bad Science, and Taste Cultures", Gastronomica 5:4 (Fall 2005). History of MSG and its marketing in Japan, Taiwan (under the Japanese), China, and the U.S.
  • Federal Register, Dec. 4, 1992 (FR 57467)
  • Federal Register, Jan. 6, 1993 (FR 2950)
  • FDA Consumer, December 1993, "Food Allergies: When Eating is Risky."

Notes

  1. ^ http://www.jpo.go.jp/seido_e/rekishi_e/kikunae_ikeda.htm
  2. ^ http://www.ajinomoto.com/amino/eng/product.html
  3. ^ http://www.ajinomoto.co.jp/ajinomoto/A-Company/company/zaimu/pdf/fact/food_biz.pdf
  4. ^ http://www.cfsan.fda.gov/~lrd/msg.html
  5. ^ http://observer.guardian.co.uk/foodmonthly/story/0,,1522368,00.html
  6. ^ Stegink LD, Filer LJ Jr, Baker GL (1985). "Plasma glutamate concentrations in adult subjects ingesting monosodium L-glutamate in consomme". American Journal of Clinical Nutrition. 42: 220–225.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Stegink LD, Filer LJ Jr, Baker GL (1987). "Plasma amino acid concentrations in normal adults ingesting aspartame and monosodium L-glutamate as part of a soup/beverage meal". Metabolism. 36 (11): 1073–1079.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ^ Himwich WA, Petersen IM (1954). "Ingested sodium glutamate and plasma levels of glutamic acid". Journal of Applied Physiology. 7 (2): 196–199.
  9. ^ Meldrum B. (1993). "Amino acids as dietary excitotoxins: a contribution to understanding neurodegenerative disorders". Brain research. Brain research reviews. 18 (3): 293–314.
  10. ^ Nemeroff, C. (1980). "Monosodium Glutamate-Induced Neurotoxicity: Review of the Literature and Call for Further Research". Nutrition & Behavior edited by Sanford A. Miller (U.S. Food & Drug Administration): 177–211.
  11. ^ Olney JW, Ho OL (1970). "Brain damage in infant mice following oral intake of glutamate, aspartate or cysteine". Nature. 227 (5258): 609–611.
  12. ^ Barinaga, M. (1990). "Amino Acids: How Much Excitement is Too Much?". Science. 247 (4938): 20–22.
  13. ^ Abraham R, Swart J, Golberg L, Coulston F. (1975). "Electron microscopic observations of hypothalami in neonatal rhesus monkeys (Macaca mulatta) after administration of monosodium-L-glutamate". Experimental and molecular pathology. 23 (2): 203–213.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  14. ^ Reynolds WA, Butler V, Lemkey-Johnston N (1976). "Hypothalamic morphology following ingestion of aspartame or MSG in the neonatal rodent and primate: a preliminary report". Journal of Toxicology and Environmental Health. 2 (2): 471–480.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  15. ^ Stegink LD, Filer LJ Jr, Baker GL (1982). "Effect of aspartame plus monosodium L-glutamate ingestion on plasma and erythrocyte amino acid levels in normal adult subjects fed a high protein meal". American Journal of Clinical Nutrition. 36 (6): 1145–1152.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  16. ^ Stegink LD, Filer LJ Jr, Baker GL (1982). "Plasma and erythrocyte amino acid levels in normal adult subjects fed a high protein meal with and without added monosodium glutamate". Journal of Nutrition. 112 (10): 1953–1160.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  17. ^ Olney JW, Sharpe LG, Feigin RD (1972). "Glutamate-induced brain damage in infant primates". Journal of Neuropathology and Experimental Neurology. 31 (3): 464–488.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  18. ^ Stegink LD; et al. (1978). "Comparative Metabolism of Glutamate in the Mouse, Monkey, and Man". Glutamic Acid: Advances in Biochemistry and Physiology (Edited: Filer LJ): 85–102. See: http://www.holisticmed.com/aspartame/abuse/stegink.jpg . {{cite journal}}: Explicit use of et al. in: |author= (help)
  19. ^ Olney JW (1984). "Excitotoxic food additives—relevance of animal studies to human safety". Neurobehavioral toxicology and teratology. 6 (6): 455–462.
  20. ^ Olney JW (1990). "Excitotoxin-mediated neuron death in youth and old age". Progress in brain research. 86: 37–51.
  21. ^ Olney JW (1984). "Excitotoxins in foods". Neurobehavioral toxicology and teratology. 15 (3): 535–544.

See also

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