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Monosodium glutamate

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Chemical structure of monosodium glutamate
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Chemical structure of monosodium glutamate

Monosodium glutamate, sodium glutamate, flavour enhancer 621 EU food additive code: E621. HS code: 29224220. (IUPAC names: 2-aminopentanedioic acid, 2-aminoglutaric acid, 1-aminopropane-1,3-dicarboxylic acid), commonly known as MSG or Vetsin, is a sodium salt of glutamic acid. MSG is a food additive, popularly marketed as a "flavour enhancer". 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).

Contents

What Is MSG?

MSG is the sodium salt of the amino acid glutamic acid. Its chemical formula is C5H8NO4Na. It is sold as a fine white crystal substance, similar in appearance to salt or sugar. Recent discoveries in the field of taste perception has demonstrated that MSG stimulates specific receptors in the tongue such as the amino acid receptor (T1R1/T1R3) or various metabotropic glutamate receptors to induce the umami taste. 
Asian cuisine originally used a natural seaweed broth, such as kelp, to bring up the umami taste in soups. Manufacturers, such as Ajinomoto, use selected strains of Micrococcus glutamicus bacteria in a bath of nutrient.  The bacteria are selected for their ability to excrete glutamic acid, which is then separated from the nutrient bath, purified, and made into its sodium salt, monosodium glutamate.  

Glutamate itself is a widespread amino acid: it is found naturally in our bodies and in protein-containing foods, such as cheese, milk, meat, peas, and mushrooms. Some of the glutamate in foods is in a "free" form; and only this free form of glutamate can enhance the flavor of foods. Part of the flavour-enhancing effect of tomatoes, certain cheeses, and fermented or hydrolyzed protein products (such as soy sauce) is therefore due to the presence of free glutamate.

Hydrolyzed proteins, or protein hydrolysates, are acid- or enzymatically treated proteins from certain foods. They contain salts of free amino acids, such as glutamate, at levels of 5 to 20 percent. Hydrolyzed proteins are used in the same manner as MSG in many foods, such as canned vegetables, soups, and processed meats.



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 "savoury" or "more-ish").



Scientific review


In 1959, 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 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 gave similar findings:

Scientific knowledge about how the body metabolizes glutamate developed rapidly during the 1980s. Studies showed that glutamate in the body plays an important role in normal functioning of the nervous system. Questions then arose on the role glutamate in food plays in these functions and whether or not glutamate in food contributes to certain neurological diseases.



Sources

Bound and unbound glutamate are found naturally in nearly every protein-rich food product, including seaweed, tomatoes, mushrooms, fermented soy products, yeast extracts, nuts, legumes, hydrolyzed proteins, and most meat and dairy products. Yet, despite its ubiquity in common food products, the flavour contributions made by glutamate and other amino acids were only scientifically identified early in the twentieth century. 



Discovery

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. [http://www.jpo.go.jp/seido_e/rekishi_e/kikunae_ikeda.htm]



Commercialization


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 [http://www.ajinomoto.com/amino/eng/product.html] of starch, sugar beets, sugar cane, or molasses. About 1.5 million metric tons were sold in 2001, with 4% annual growth expected. [http://www.ajinomoto.co.jp/ajinomoto/A-Company/company/zaimu/pdf/fact/food_biz.pdf] MSG is used commercially as a flavour enhancer, and is added as an ingredient to many snack foods, frozen dinners, and instant meals such as the seasoning mixtures for instant noodles.



Alternate names

In Chinese, it is known as wèijīng (), meaning the same as the Japanese name, but using Chinese grammar and character variants (note the first character is identical).


In Korea it is called mi-won.


In Japan, an alternate, generic name for the compound (as Ajinomoto is a registered trademark) is gurutamin san'natoriumu (グルタミン酸ナトリウム) literally meaning "glutamine acid sodium" or "salt of glutamic acid".


In the Philippines, it is known as vetsin (might be derived from wèijīng).



Health concerns



MSG intolerance

There have been reports of allergies and/or sensitivities to MSG, sometimes attributed to the free glutamic acid component, which has been blamed for causing a wide variety of physical symptoms such as migraines, nausea, digestive upsets, drowsiness, heart palpitations, asthma, anaphylactic shock, and many other complaints. "Chinese restaurant syndrome" is often used as an example of the symptoms purported to be caused by MSG. 


Prompted by continuing public interest and a flurry of glutamate-related studies in the late 1980s, FDA contracted with FASEB in 1992 to review the available scientific data. The agency asked FASEB to address 18 questions dealing with:


FASEB held a two-day meeting and convened an expert panel that thoroughly reviewed all the available scientific literature on this issue. 
FASEB completed the final report, over 350 pages long, and delivered it to FDA on July 31, 1995. While not a new study, the report offers a new safety assessment based on the most comprehensive existing evaluation to date of glutamate safety. 
Among the report's key findings: 



Choi, D.W., and Rothman. S.M. The role of glutamate neurotoxicity in hypoxic-ischemic neuronal death. Annu Rev Neurosci 13: 171-182, 1990.Olney, J.W. Excitotoxic amino acids and neuropsychiatric disorders. Annu Rev Pharmacol Toxicol 30: 47-71, 1990.
Coyle, J.T. Glutamate receptors and age-related neurodegenerative disorders. Biol Psychiatry 27: 91A, 1990.Pomara, N., Deptula, D., Singh, R., LeWitt, P.A., and Banay-Schwartz, M. Excitatory amino acid concentrations in CSF of patients with Alzheimer's disease. Biol Psychiatry 27: 91A, 1990.Olney, J.W. Excitotoxins and neurological diseases. Proceedings of the 11th International Congress of Neuropathology, Kyoto, Japan, September 2-8, 1990.


Obesity


MSG has been used in newborn laboratory mice [to induce adult obesity] because of the lesions that it provokes in the arcuate nucleus of the hypothalamus. However, the blood-brain barrier (BBB) of newborn babies doesn't resemble the one of neonate mice, therefore, like in adults, glutamate has a low penetration level in the central nervous system[link]. Only the luminal membrane of the BBB contains facilitative carriers for glutamine and glutamate. In fact, the amount of [free glutamate in breast milk] is one of the highest among other mammals besides the chimpanzee.



Excitotoxicity

Glutamic acid is an amino acid commonly found in foods. 
Because MSG is absorbed very quickly (unlike glutamic acid-containing proteins in foods), it is 
known that MSG could spike blood plasma levels of glutamate.    Glutamic acid is in a class of chemicals known as excitotoxins. Abnormally high levels of excitotoxins have been shown in hundreds of 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.   The debate among scientists on the significance of these findings has been raging since the early 1970's, when Dr. John Olney found that high levels of glutamic acid caused damage to the brains of infant mice.  The debate is complex and has focused on several areas:
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. 


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.   While they agree that the combined effects of all food-based excitotoxins should be considered , 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.  Other scientists feel that primates are susceptible to excitotoxic damage  and that humans concentrate excitotoxins in the blood more than other animals.  Based on these findings, they feel that humans are approximately 5-6 times more susceptible to the effects of excitotoxins than rodents are.  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  and the potential long-term neurodegenerative effects of small-to-moderate spikes on plasma excitotoxin levels. . And yet, although may seem as a contradiction, human breast milk is one of the milks with the highest levels in free glutamate among mammals. 





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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 foods whose labels say "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.



European Union


MSG has the E number E621 and is hence usually listed as "flavour enhancer E621".



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