monosodium glutamate

Monosodium glutamate
IUPAC name	Sodium (2S)-2-amino-5-hydroxy-5-oxo-pentanoate
Identifiers
CAS number	[142-47-2]
PubChem	85314
SMILES	C(CC(=O)O)C(C(=O)[O-])N.[Na+]
ChemSpider ID	76943
Properties
Molecular formula	C5H8NNaO4
Molar mass	169.111 g/mol
Appearance	white crystalline powder
Melting point	225 °C, 498 K, 437 °F
Solubility in water	very soluble in water
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

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 used to be 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. 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 'Ajinomoto' means "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][not in citation given]}

Examples include:

• Pre-prepared stocks often known as stock cubes or bouillon cubes.
• Condiments such as barbecue sauce and salad dressing.
• Canned, frozen, or dried prepared food
• Common snack foods such as flavoured potato chips and flavoured tortilla chips.
• Seasoning mixtures

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

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]

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 BMI (Body Mass Index).^[16]

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

Food portal

• Ajinomoto Co., Inc.
• Umami
• Excitotoxicity
• Flavour enhancer
• Disodium glutamate
• List of food additives
• Yeast extract

References

External links

• [1] MSG Discussion Board
• MSG: A Common Flavor Enhancer (FDA)