Shizuko Yamaguchi

Basic properties of umami and effects on humans

This is a review of the taste of umami substances, and some related findings. The data demonstrate that, though the taste of the common umami substances such as MSG and IMP is mainly caused by their anions, the effects of their cations, such as Na, should not be ignored. The effects of cations approach the taste thresholds of umami substances. Although the taste threshold of MSG was slightly lower than that of Na, the threshold of IMP was found to be controlled by Na. However, the degree of saltiness was less than 10% above the threshold of the equivalent weight of NaCl. It was also found that the taste of IMP was probably caused by glutamic acid in saliva, since IMP itself has no umami taste. That is, IMP enhances the umami taste of MSG. Finally, comparison of umami sensitivity of Japanese and Americans revealed no difference.

Independence and Primacy of Umami as Compared with the Four Basic Tastes

Umami is defined as the taste elicited by monosodium glutamate (MSG) or 5‘ribonucleotides such as IMP and GNP. In this paper, several lines of evidence indicate that umami is independent and “basic” as long as the so-called four basic tastes are regarded as basic. In the first experiment, the similarities among the four tastes (sucrose, NaC1, tartaric acid, and quinine sulfate) and umami (MSG) in single and mixture solutions were examined. A multidimensional scaling yielded a spatial configuration reflecting the similarities among the stimuli. All the stimuli were located within a four-dimensional regular polyhedron that has five vertices. The tastes composed of the four basic tastes were located within a three-dimensional tetrahedron, which was a subcomplex of the four-dimensional polyhedron with the four basic tastes located at four vertices. Umami was located at the other vertex, indicating that it constructs another dimension independent of the four basic tastes. Another multidimensional scaling showed the dominance of umami in the tastes of natural foods. The tastes of broths made from meats (beef, pork, etc.) and fish fell outside the tetrahedron of the four basic tastes and were located close to umami. Those made from vegetables widely distributed around the five taste areas. However, when a small amount of IMP was added, the tastes approached umami due to the remarkable synergistic effect between IMP and glutamic acid contained naturally in the vegetable stocks. Thus the stocks examined were regarded to have dominant or potential umami, which is actualized or developed by a small amount of umami substances. Umami did not enhance the four basic tastes, and vice versa, at threshold and at suprathreshold levels. The hedonic properties of umami were examined in comparison with the four basic tastes. As far as simple aqueous systems were concerned, umami did not cause a pleasant sensation. In the selected flavored solutions or actual foods, umami clearly enhanced the hedonic tone. Umami increased the pleasantness of foods only within a certain range of concentration, and an excess of umami caused a rather unpleasant sensation by which the intake concentration became self-limited. These hedonic properties were similar to other basic tastes except for sweetness.