Monosodium glutamate(IUPAC name- 2-Aminopentanedioic acid,2-Aminoglutaric acid,1-Aminopropane-1,3-dicarboxylic acid), commonly known as MSG, is a salt of sodium with glutamic acid. It is best known for its use 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.
MSG triggers the (recently identified) taste buds sensitive to umami, one of the five basic tastes (the word umami is a loanword from Japanese; is also sometimes referred to as "savoury" or "more-ish"). It is believed that "umami" taste buds respond specifically to glutamate in the same way that "sweet" ones respond to sugar.
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. In addition to being one of the building blocks in protein synthesis, it is also important in brain function, as an excitatory neurotransmitter. Free glutamic acid cannot cross the blood-brain barrier in appreciable quantities; instead it is converted into L-glutamine, which the brain uses for fuel and protein synthesis.
MSG is found naturally in seaweed and fermented soy products, and especially yeast extracts. Smaller quantities are also present in tomatoes, mushrooms, and Parmesan cheese. It is used commercially in much greater concentrations, adding extra flavour to snack foods, frozen dinners, and instant meals such as the seasoning mixtures for instant noodles. Much of the usage is due to the fact that it is cheaper to increase the MSG content than to increase the amount of other flavoring ingredients.
MSG was first discovered and patented by Japanese researcher Kikunae Ikeda of the Tokyo Imperial University, who successfully crystallized the substance out of seaweed broth. It was first sold commercially under the Ajinomoto ("essense of taste"; 味の素) brand in Japan. Modern commercial MSG is produced by fermentation of starch, sugar beet, sugar cane, or molasses. About 1.5 million metric tons were sold in 2001, with 4% annual growth expected.
Some people believe they are allergic or sensitive to MSG, and it has been blamed for causing a wide variety of physical symptoms such as migraines, nausea, digestive upsets, drowsiness, heart palpitations, asthma and myriad other complaints all the way up to anaphylactic shock. Symptoms that have sometimes been mistaken for heart attacks or allergic reactions are sometimes called "Chinese Restaurant Syndrome". A considerable amount of research and testing into MSG allergies has been performed over the past few decades, and the vast majority of controlled studies show no link at all between glutamate in food and any allergic reaction. Critics of the testing believe that the tests were unfairly biased towards finding no result. In particular, they consider flawed a 1993 study in which aspartame was used in the placebo, because aspartame itself has been accused of causing many of the same symptoms as MSG sensitivity in susceptible people. Some researchers have suggested that specific individuals might be hypersensitive to MSG while others are entirely unaffected by it, but no conclusive results have emerged to demonstrate the validity of this hypothesis. While the worries of the general public over the content of MSG in foods reached near hysterical levels in the 1980s, interest in the issue has since almost completely abated and today there is generally very little concern over MSG content of foods.
Nonetheless, there are still some small groups (especially those in alternative medicine) who consider MSG to be a potent neurotoxin which is yielding mass neurological retardation in affected populations. This view is generally looked upon by mainstream scientists as being preposterous and pseudoscientific, since there is essentially no scientific data which supports the claim.
The United States Food and Drug Administration lists monosodium glutamate as "generally recognized as safe", along with salt, vinegar, baking powder, and sodium tripolyphosphate.
Despite this, many American Chinese restaurants have taken to advertising "No MSG" menus. More traditional establishments both in Western countries and in China make no such efforts, but gourmet chefs tend to view the excessive usage of MSG as cheating and some of the more opinionated ones eschew it entirely.
Food products from Australia and New Zealand may refer to MSG as "flavour enhancer 621". The EU food additive code for MSG is E621. 29224220 is the HS code of monosodium glutamate.