Monosodium glutamate, 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.
MSG triggers the (recently identified) taste buds[?] sensitive to umame, one of the five basic tastes; this flavor is considered basic in Japanese and Chinese cooking (the word umame is Japanese), but not discussed as much in Western cuisine, where it is sometimes referred to as "savoury" or "more-ish". It is believed that "umame" 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.
MSG was first isolated in 1908 by Kikune Ikeda of the Tokyo Imperial University, who successfully crystallized the substance out of seaweed broth. Modern commercial MSG is produced by fermentation of starch, sugar beet, sugar cane, or molasses.
Many 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 a myriad of other complaints all the way up to anaphylactic shock. 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, and also because volunteers with asthma, allergies, migraines or other symptoms of potential susceptibility were automatically excluded from the test group. 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 along those lines.
The United States Food and Drug Administration lists monosodium glutamate as "generally recognized as safe", along with salt, vinegar, and baking powder. In East Asia it is sometimes included in nutritional supplements.