Monosodium glutamate

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Image:MSG.png 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).

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What Is MSG?

MSG is the sodium salt of the amino acid glutamic acid and a form of glutamate. It is sold as a fine white crystal substance, similar in appearance to salt or sugar. Many scientists believe that MSG stimulates glutamate receptors in the tongue to augment meat-like flavours.

Asian cuisine originally used a seaweed broth to obtain the flavour-enhancing effects of MSG. Today, the major process for MSG manufacturing is by a fermenting process using starch, sugar beets, sugar cane, or molasses. 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 in many living things: it is found naturally in our bodies and in protein-containing foods, such as cheese, milk, meat, peas, and mushrooms. Some glutamate is in foods in a "free" form. It is only in this free form that glutamate can enhance a food's flavour. Part of the flavour-enhancing effect of tomatoes, certain cheeses, and fermented or hydrolyzed protein products (such as soy sauce) is 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.

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Umami

MSG triggers the (recently identified) taste buds which are sensitive to umami, one of the five basic tastes (the word umami is a loanword from Japanese; it is also sometimes referred to as "savoury" or "more-ish"). It is believed that "umami" taste buds respond specifically to certain amino acids (such as glutamic acid) in the same way that "sweet" taste buds respond to sugars.

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Natural amino acid

Glutamic acid is one of the twenty amino acids that make up human proteins; it is critical for proper cell function, but not considered an essential nutrient because the body can manufacture it from simpler compounds. It is one of the building blocks in protein synthesis.

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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:

  • A 1991 report by the European Communities' (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".
  • Also, the 1987 Joint Expert Committee on Food Additives of the United Nations Food and Agriculture Organization and the World Health Organization have placed MSG in the safest category of food ingredients.

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.

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Neurotransmitter

MSG is also important in brain function as an excitatory neurotransmitter. Free glutamate cannot cross a healthy person's blood-brain barrier in appreciable quantities; instead, it is converted into L-glutamine, which the brain uses for fuel and protein synthesis. However, in individuals with weakened blood-brain barriers, such as young children (barrier is still developing) and the elderly (barrier is degenerating), or those with weakened blood-brain barriers due to genetic defects, free glutamate in the blood can cross the blood-brain barrier, causing brain cell death by over-excitation. This phenomenon appears to be linked to brain lesions, particularly in the hypothalamus, and may be linked to such neurodegenerative diseases as Parkinson's disease, Alzheimer's disease, ALS, and more.

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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.

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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. <ref>http://www.jpo.go.jp/seido_e/rekishi_e/kikunae_ikeda.htm</ref>

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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 <ref>http://www.ajinomoto.com/amino/eng/product.html</ref> of starch, sugar beets, sugar cane, or molasses. About 1.5 million metric tons were sold in 2001, with 4% annual growth expected. <ref>http://www.ajinomoto.co.jp/ajinomoto/A-Company/company/zaimu/pdf/fact/food_biz.pdf</ref> 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.

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Alternate names

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

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".

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Health concerns

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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 a myriad of 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:

  • the possible role of MSG in eliciting MSG symptom complex
  • the possible role of dietary glutamates in forming brain lesions and damaging nerve cells in humans
  • underlying conditions that may predispose a person to adverse effects from MSG
  • the amount consumed and other factors that may affect a person's response to MSG
  • the quality of scientific data and previous safety reviews.

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:

  • 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
    • weak pulse
    • violent dreams
    • bronchospasm (difficulty breathing) in MSG-intolerant people with asthma
    • drowsiness
    • weakness.
  • In otherwise healthy MSG-intolerant people, the MSG symptom complex tends to occur within one hour after eating 3 grams or more of MSG on an empty stomach or without other food. A typical serving of glutamate-treated food contains less than 0.5 grams of MSG. A reaction is most likely if the MSG is eaten in a large quantity or in a liquid, such as a clear soup.
  • Severe, poorly controlled asthma may be a predisposing medical condition for MSG symptom complex.
  • No evidence exists to suggest that dietary MSG or glutamate contributes to Alzheimer's disease, Huntington's chorea, amyotrophic lateral sclerosis, AIDS dementia complex, or any other long-term or chronic diseases.
  • No evidence exists to suggest that dietary MSG causes brain lesions or damages nerve cells in humans.
  • The level of vitamin B6 in a person's body plays a role in glutamate metabolism, and the possible impact of marginal B6 intake should be considered in future research.
  • There is no scientific evidence that the levels of glutamate in hydrolyzed proteins causes adverse effects or that other manufactured glutamate has effects different from glutamate normally found in foods.
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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. <ref>Template:Cite journal</ref> <ref>Template:Cite journal</ref> <ref>Template:Cite journal</ref> Glutamic acid is in a class of chemicals known as excitotoxins. Abnormally high levels of excitotoxins have been shown in hundreds of animals 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. <ref>Template:Cite journal</ref> <ref>Template:Cite journal</ref> 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. <ref>Template:Cite journal</ref> 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.
  • Whether neurotoxicity from excitotoxins should consider the combined effect 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. <ref>Template:Cite journal</ref>

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. <ref>Template:Cite journal</ref> <ref>Template:Cite journal</ref> While they agree that the combined effects of all food-based excitotoxins should be considered <ref>Template:Cite journal</ref>, 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. <ref>Template:Cite journal</ref> Other scientists feel that primates are susceptible to excitotoxic damage <ref>Template:Cite journal</ref> and that humans concentrate excitotoxins in the blood more than other animals. <ref>Template:Cite journal</ref> Based on these findings, they feel that humans are approximately 5-6 times more susceptible to the effects of excitotoxins than rodents are. <ref>Template:Cite journal</ref> 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 <ref>Template:Cite journal</ref> and the potential long-term neurodegenerative effects of small-to-moderate spikes on plasma excitotoxin levels. <ref>Template:Cite journal</ref>

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Ingredient listing

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 flavourings".

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.

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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."
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Notes

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See also

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External links

bg:Мононатриев глутамат cs:Glutaman sodný da:Mononatriumglutaminat de:Mononatriumglutamat es:Glutamato monosódico he:מונוסודיום גלוטמט nl:Mononatriumglutamaat ja:グルタミン酸ナトリウム pl:Glutaminian sodu ru:Глутамат натрия sk:Glutaman sodný sv:Natriumglutamat th:ผงชูรส zh:味精

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