Salivary secretion elicited by taste stimulation with umami substances in human adults

Salivary secretion from the parotid gland was measured when umami substances (monosodium L-glutamatc, disodium 5′-inosinate and disodium 5′-guanylate) were applied to the anterior or posterior parts of the tongue in human adults. The amount of secretion induced by a low concentration (0.01 M) of umami substances was very small and similar to that elicited by 1 M sucrose. Salivation induced by a high concentration (0.1 M) of umami substances was about twice that induced by the low concentration, but less than that induced by 0.1 M NaCl. The volume of secretion induced by a mixture containing the low concentration of both monosodium L-glutamate and disodium 5′-inosinate (or disodium 5′-guanylate) approximated the arithmetic sum of secretions induced by the individual components, whereas a mixture of the high concentration of these substances elicited much less salivation than the sum of secretions for the components. More copious flow of parotid saliva tended to be induced from stimulating the posterior tongue compared to the anterior tongue. The present results are discussed in terms of the taste properties of umami substances as shown in previous psychophysical and elcctrophysiological studies.