Monosodium Glutamate - Food Flavor Potentiator - Food Chemistry

In a strictly chemical sense, MSG's chemical interactions are what one would expect them to be according to theory and proven facts. Chemical syntheses to and from MSG are what you'd expect.

MSG has a variety of uses that rely on it solely for its chemical properties--such as using it to prepare glutamic acid, or as a biologically compatible glutamic acid source in solution.

But MSG's taste effects can't be explained on a chemical or biological basis alone. MSG's taste enhancing properties also involves human genetics, physiology, and psychology. Its taste effect, although chemically the same, may be physiologically and psychologically different for each individual partaking in it.

Studies of preferences of tasters have been mostly for foods with and without added MSG. However, physiological and biochemical effects of the taste sensation have also been studied. MSG's effect works best in the pH range of 3.5 to 7.2 (mostly "acidic"), which also is the range that most foods possess. MSG is useful for intensifying the flavor of high-protein foods such as meat, fish, eggs, and cheese. But it doesn't work with fruits, fruit juices, sweet spicy foods, or any other foods rich in sugar and carbohydrates.

But when it does work, MSG also intensifies bad flavors. Therefore, meat products made from old and tainted meat do not have MSG in ingredients. Instead, peppery and spicy seasoning would be added to anesthetize taste buds, masking the flavor of spoilage.

Food characteristics such as fats, oils, and high viscosity also modify MSG's influence.

Beef extract, hydrolyzed vegetable proteins, casein digests, and yeast autolyzate extracts contain a mix of common amino acid, peptide, protein, nucleotide, and "browning reaction" flavorings. Through hydrolysis and neutralization reactions in a chemistry lab, these flavor "mixes" can be separated and purified to yield flavor potentiators such as MSG. MSG is to these crude components that sugar is to molasses.

MSG is synergistic (works even better) with its fellow "mix components", as well as being synergistic with other flavor potentiators. Flavor potentiation refers to the "action of a compound which, in small quantities, has by itself no sensory effect, but exaggerates the effect of other agents on the system."

There are two groups of known flavor potentiators:

• certain L-amino acids containing five carbon atoms (to which MSG, ibotenic acid, and tricholomic acid belong)


• certain 5'-nucleotides containing 6-hydroxypurine (to which 5'-guanylate or guanosine 5'-monophosphate (5'-GMP), 5'-inosinate or inosine 5'-monophosphate (5'-IMP), and 5'-xanthylate or xanthosine 5'-monophosphate (5'-XMP) belong)

The nucleotides are usually used in the form of sodium salts--therefore, they can also be termed as disodium guanylate (DSG), disodium inosinate (DSI), and disodium xanthylate (DSX). A specific synergistic action in flavor exists between a compound of the first group and a compound of the second group. The ribonucleotides (derived from muscle and yeast RNA by acid hydrolysis, then neutralized with NaOH) have essentially the same flavor enhancing property as MSG but are ten times as powerful. They are even more effective when mixed with MSG.

Through extensive studies, Kuninaka (1967) and associates have determined that for the nucleotide potentiators, the ribosidic and 5'-phosphomonoester linkages are necessary for taste potentiation. Further studies have indicated that the two phospho-hydroxy groups are also necessary for this effect.

Tricholomic acid and ibotenic acid (both isolated from the fungi Tricholoma muscarium and Amanita strobiliformis respectively) have the same general structure as MSG and have essentially the same flavor potentiating effect. But unlike MSG. DSI, and DSG, which are available to the consumer, tricholomic acid and ibotenic acid are undergoing closer scrutiny than the majority of flavor effect substances.

This is because it is well known in Japan that the fungi that they are isolated from are deadly to flies. Amanita sp. in particular are well known in the U.S.A. as extremely toxic for human consumption. Consequently these last two amino acids will be exhaustively studied before they are allowed on the consumer's table.

Theories on these flavor potentiators' mechanisms are many. Pryde (1973) stated that MSG could increase taste bud sensitivity, stimulate greater saliva flow, and combine with trace metals present, thus freeing additional taste bud receptor sites to react with the taste stimulating compounds present. Majtenyi (1974) also mentioned the above theories, but added that it was nucleotide binding of metal ions that sensitized tasting sites otherwise not active in the enhancement of flavors.

MSG is used at a level of one-tenth the concentration of salt used in food. Its use is restricted to protein food. From this, the impact of MSG on the American diet can be realized. In the United States alone about 30 billion pounds of protein foods are seasoned with MSG annually (approximately 150 pounds per person per year) (Smith and Minor, 1974). This use is increasing rapidly.

Convenience foods particularly benefit from the addition of MSG and there may be some preservative qualities associated with its use. MSG is often poured quite liberally on restaurant foods. Soups, stews, and other related foods use MSG extensively. Artificial sake (rice wine) consumed in Japan is made by blending known ingredients found in natural sake, including MSG. It is made by blending ethanol, glucose, succinic acid, lactic acid, inorganic phosphates, sodium chloride, MSG, glycine, and alanine. Dipeptides of Gly-L-Leu, L-Val-L-Glu were also added to improve body, increase the complexity and balance of taste, and serve as buffering agents. Even certain drugs contain MSG, for example, Glutavine.

Being an amino acid, MSG has been regarded as harmless. But there may be unpleasant effects when large amounts are consumed. Some people have low thresholds of sensitivity to MSG--a "Chinese Restaurant Syndrome" (CRS) has been medically recognized as their reaction to ingestions of MSG. CRS includes these symptoms: burning sensation in the back of the neck spreading to the forearms and to the anterior thorax, accompanied by a feeling of infraorbital tightness, pressure, substernal discomfort, headaches, temporary weakness and numbness, loss of breath, fainting, and other symptoms resembling heart disease.

Since MSG is derived from glutamic acid, the most abundant protein building block in nature, those who are allergic or sensitive to proteins may also be sensitive to MSG. But avoiding MSG is extremely difficult. Even a careful reading of all labels will not uncover the products to which MSG may be legally added. More than ten thousand processed foods contain MSG, and many, such as mayonaise, French dressing, and salad dressing do not have to list MSG if it is used. Although glutamate is present in all proteins in the body, an excess amount can become toxic and destroy nerve cells. This has caused a dilemma in the food industry. Food companies cannot be relied upon to police themselves. They have acquired the assumption that a product can remain on the market until definitely proven dangerous.