|Molar mass||169.111 g/mol|
|Appearance||white crystalline powder|
225 °C, 498 K, 437 °F
|Solubility in water||74g/100mL|
(what is this?) |
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Monosodium glutamate, also known as sodium glutamate and nmg, is a sodium salt of the naturally occurring 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 was once predominantly made from wheat gluten, but is now mostly made from bacterial fermentation; it is acceptable for celiacs following a gluten-free diet.
Although traditional Asian cuisine had often used seaweed extract, which contains high concentrations of glutamic acid, it was not until 1907 that MSG was isolated by Kikunae Ikeda. MSG was subsequently patented by Ajinomoto Corporation of Japan in 1909. In its pure form, it appears as a white crystalline powder which rapidly dissociates into sodium cations and glutamate anions on contact with water (glutamate is the anionic form of glutamic acid).
MSG is normally obtained by the fermentation of carbohydrates and by using bacterial or yeast species from genera such as Brevibacterium, Arthrobacter, Microbacterium, and Corynebacterium. Yields of 100 g/litre  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.
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.
The Ajinomoto company was formed to manufacture and market MSG in Japan; the name 'Aji no moto' translates to "essence of taste". It was introduced to the United States in 1947 as Ac'cent flavor enhancer.
Modern commercial MSG is produced by fermentation of starch, sugar beets, sugar cane, or molasses. About 1.5 million tonnes were sold in 2001, with 4% annual growth expected. 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.
Only the L-glutamate enantiomer has flavour-enhancing properties. 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.
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 United States Food and Drug Administration (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" and/or a worsening of asthmatic symptoms. 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. 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. 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.
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, which must be labelled with these common and usual names. Since 1998, these cannot be included in the term "spices and flavorings". 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. The food additives disodium inosinate and disodium guanylate, which are nucleic acids, are usually used as substitutes for monosodium glutamate-containing ingredients.
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."
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 an increased Body Mass Index (BMI).
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.