Health & Welfare: Gourmet Chemistry

Sandy Shaw and Durk Pearson | From the February 1983 issue

A knowledge of biochemistry can enable you to improve the quality of your life in many ways. The enjoyment of food is an important goal in itself, as well as being an important consideration in nutrition. Indeed, loss of flavor perception with age is a major factor in malnutrition of the elderly. We explain here the sources of a significant flavor contribution to foods like meats, fish, and vegetables and how to markedly enhance their flavor in your own diet.

Have you ever shot a pheasant or caught a fish and cooked and eaten it within a few hours? If so, you have probably noticed an ineffable freshness and an intensity of flavor that is sorely lacking even in finest gourmet cuisine. This splendid taste experience is not due to awakening at 5:00 A.M., hiking through frozen fields, or shooting the bird yourself; it still tastes special if a friend bags it and promptly brings it home to you. The ineffable is now quite effable due to advances in modern flavor science. Two important flavor components of this "fresh" taste, IMP and GMP, degrade very rapidly after the animal's death, even if the carcass is quickly frozen.

In 1908, a Japanese scientist discovered a flavor quality called "umami" that provides the basic flavors to meats, poultry, fish, dairy products, and vegetables. The "umami" taste is attributed mainly to MSG (monosodium glutamate) and nucleotides (basic chemical building blocks of nucleic acids, RNA and DNA). These two entities are the basis of, but do not necessarily constitute all of "umami," which is the overall result of a mixture of amino acids, peptides, nucleotides, organic acids, and inorganic ions. In addition to its contribution to taste, "umami" also adds flavor characteristics such as mouth fullness, impact, and thickness.

The MSG and nucleotides affect how we perceive the basic tastes sour and bitter. The threshold concentrations of sour and bitter are increased (it takes more of either before we notice it) but there is no detectable effect on the threshold concentrations of salt and sweet tastes. The MSG and nucleotides together are synergistic; that is, their combined flavor effect is greater than additive. As people age, they tend to develop taste deficits. A major problem is a decrease in sensitivity to salt and sweet, with a resulting predominance of sour and bitter flavor notes. By modulating sour and bitter tastes, the MSG and nucleotides may be of particular benefit to older people.

In meat, for example, major flavor elements include MSG, IMP (inosine monophosphate), succinic acid, lactic acid, phosphoric acid, and pyrrolidone-carboxylic acid. In potatoes and other plant tissues, RNA is broken down by enzymes during heat processing, resulting in the formation of nucleotides such as IMP and GMP (guanosine monophosphate), important flavor elements. Glutamate is another important source of flavor in fresh vegetables. This natural glutamate content declines by up to 50 percent during the first 24 hours after harvest, depending on handling and storage conditions. Replacing the lost glutamate improves the flavor, as demonstrated in taste tests.

In freshly killed fish muscle, IMP is accumulated as a degradation product of ATP (adenosine triphosphate, the primary energy-storage molecule). The IMP is then slowly degraded to hypoxanthine, a strongly bitter substance. This bitter taste, sometimes found in stored frozen fish, may be a result of bacterial interaction with hypoxanthine rather than hypoxanthine alone.

Several Japanese firms produce a yeast that makes large quantities of MSG and the nucleotides IMP and GMP and from which these substances are extracted. When they are combined in the ratio of 90 percent MSG to 10 percent nucleotides (5 percent each of IMP and GMP) and sprinkled on foods like salt, the effect is a dramatic enhancement of the taste of meats, fish, poultry, dairy products, and vegetables. We carry containers of it in our cars so that when we eat at a restaurant, we'll be able to increase our enjoyment. It is particularly effective on bacon and other meats, gravies, soups, casseroles, and vegetables. This flavor enhancer is used at a level similar to that of salt, but it enhances flavors over a far wider range of concentrations than salt does and is much less likely to "ruin" the taste of the food through overuse.

Although a product containing MSG and IMP and GMP in this ratio is available in the marketplace (such as in some Japanese specialty gourmet stores under the trade name Flave®), it is not commonly found. A few prepared dry-food mixes (to which meat or fish are added) commonly found on supermarket shelves do use these remarkable flavor enhancers. The nucleotides are usually listed on the label as disodium inosinate and disodium guanylate. Most such products that we have tried, however, have been remarkably bland and unimaginative, something that can't be corrected with the flavor enhancers alone. Enhancement works best on high-quality, well-prepared and well-seasoned food. We consider it a gourmet's delight!

One final note: Individuals with a sensitivity to MSG should avoid large doses of it, particularly on an empty stomach; usually this response (the so-called Chinese Restaurant Syndrome, caused by dilation of the blood vessels and a release of tissue histamines) is triggered by several grams of MSG on an empty stomach, not the several milligrams (one gram equals 1,000 milligrams) used for food flavor enhancement. Few people realize that MSG is a major constituent of the human body. The average human body contains about 4½ pounds of the amino acid glutamate. Persons who must restrict the sodium in their diet should not use monosodium glutamate, disodium inosinate, or disodium guanylate except with the advice of their physician.

When we were attending a restaurant trade show not too long ago, we were amazed to find that nobody we spoke to had any knowledge of these important flavor components other than a superficial awareness of MSG, and nobody was using them to enhance the flavor of their restaurant foods. While great cooking is an art, science has much to offer the fine chef. A chef with excellent intuition about what will taste good will not be able to compete with a chef having similar intuition and also understanding some of the biochemistry that explains why food tastes good.

A list of scientific literature on this topic is available through REASON. Send a stamped, self-addressed envelope and ask for H&W references, February.