Manufacturers, such as Ajinomoto, use selected strains of Corynebacterium glutamicum bacteria in a nutrient-rich medium. The bacteria are selected for their ability to excrete glutamic acid, which is then separated from the nutrient medium and processed into its sodium salt, monosodium glutamate. Rome
In the Roman Empire glutamic acid was found in a sauce called garum, made from fermenting fish in saltwater. The flavor enhancing properties of glutamic acid allowed Romans to reduce the use of expensive salt. Concentration in foods
The following table illustrates the glutamate content of some selected common foods. Free glutamate is the form directly tasted and absorbed whereas glutamate bound in protein is not available until further breakdown by digestion or cooking. In general, vegetables contain more free glutamate but less protein-bound glutamate. Hydrolyzed protein
Hydrolyzed proteins, or protein hydrolysates, are acid- or enzymatically treated proteins from certain foods. One example is yeast extract. Hydrolyzed protein contains free amino acids, such as glutamate, at levels of 5% to 20%. Hydrolyzed protein is used in the same manner as monosodium glutamate in many foods, such as canned vegetables, soups, and processed meats. Safety as a flavor enhancer
Studies
Monosodium glutamate (MSG) is regarded as safe for consumption. An association between MSG consumption and a constellation of symptoms has not been demonstrated under rigorously controlled conditions. Techniques used to adequately control for experimental bias include a placebo-controlled double-blinded experimental design and the use of capsules to deliver the compound to mask the strong and unique after-taste of glutamates.
The FASEB report reaffirmed the safety of MSG when it is consumed at usual levels by the general population, and found no evidence of any connection between MSG and any serious long-term reactions.Under 2003 U.S. Food and Drug Administration regulations, when monosodium glutamate is added to a food, it must be identified as "monosodium glutamate" in the labels ingredient list. Because glutamate is commonly found in food, primarily from protein sources, the FDA does not require foods and ingredients that contain glutamate as an inherent component to list it on the label. Examples include tomatoes, cheeses, meats, hydrolyzed protein products such as soy sauce, and autolyzed yeast extracts. These ingredients are to be declared on the label by their common or usual names. The term natural flavor is now used by the food industry when using glutamic acid. Because of lack of regulation, it is impossible to determine what percentage of natural flavor is actually glutamic acid. The food additives disodium inosinate and disodium guanylate are usually used in synergy with monosodium glutamate-containing ingredients, and provide a likely indicator of the addition of glutamate to a product. As of 2002 the National Academy of Sciences Committee on Dietary Reference Intakes had not set a NOAEL or LOAEL for glutamate. Australia and New Zealand
Standard 1.2.4 of the Australia New Zealand Food Standards Code requires the presence of monosodium glutamate as a food additive to be labeled.