Taste space, umami

Mathematical Consideration of the Synergistic Effect. Generalizing the above-mentioned results, we can introduce a concept of an umami taste space. The umami solution of any combination of the two groups of umami substances can be expressed as a point in a space of 2-dimensions, say, G, defined as follows ... 

To be concrete, if we take MSG and IMP as the standards for both groups of substances, u and v represent the totals of acidic amino acids and nucleotides in terms of the concentrations of MSG and IMP, respectively. In our taste space, the sum means combining the components of two solutions, and the scalar multiple means concentrating or diluting of a solution. The absolute value means the intensity of umami of a solution in terms of the concentration of, say, MSG alone. 

A persistent idea is that there is a very small number of flavor quaUties or characteristics, called primaries, each detected by a different kind of receptor site in the sensory organ. It is thought that each of these primary sites can be excited independently but that some chemicals can react with more than one site producing the perception of several flavor quaUties simultaneously (12). Sweet, sour, salty, bitter, and umami quaUties are generally accepted as five of the primaries for taste sucrose, hydrochloric acid, sodium chloride, quinine, and glutamate, respectively, are compounds that have these primary tastes. Sucrose is only sweet, quinine is only bitter, etc saccharin, however, is slightly bitter as well as sweet and its Stevens law exponent is 0.8, between that for purely sweet (1.5) and purely bitter (0.6) compounds (34). There is evidence that all compounds with the same primary taste characteristic have the same psychophysical exponent even though they may have different threshold values (24). The flavor of a complex food can be described as a combination of a smaller number of flavor primaries, each with an associated intensity. A flavor may be described as a vector in which the primaries make up the coordinates of the flavor space. 

By contrast, flavor space is difficult to define. Taste, of course, has its traditional four qualities—sweet, salt, sour, and bitter—and possibly a fifth, umami. However, smell seems to have a virtually limitless odor space. It is common to say that a human can identify up to 10,000 different odors, but that number as far as I can determine is only a speculation. Since odors are the main component of most flavors, flavor space is correspondingly difficult to define. This underlines the reason why no description of brain mechanisms in flavor can arise until there is a better understanding of the complex roles of the mechanisms in smell. 

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