On the taste of umami in chimpanzee

Whole and single fiber chorda tympani nerve recordings were obtained in 5 chimpanzees to stimulation with MSG (monosodium phosphate) and GMP (guanosine 5'-monophosphate, disodium salt) alone and in combination. The overall chorda tympani nerve activity was recorded to 5 concentrations of MSG, ranging from 1 to 100 mM with and without 0.3 mM GMP, and to 5 concentrations of GMP, ranging from 0.1 to 10 mM, with and without 30 mM MSG. A synergistic effect was recorded between MSG and GMP in 3 out of 4 animals. The effect of stimulation with MSG and GMP alone and mixed was studied in approximately 25 single fiber recordings against a background of the stimulating effects of 11 different sweeteners, 3 acids, 3 bitter compounds and 3 different salts. The fibers showed a high taste specificity and fell into groups which corroborated with the human concepts of the taste qualities. The umami compounds elicited moderate responses which were largest in the sweet fibers. In the 6 sweet fibers that responded to the umami compounds. 0.3 mM GMP was a more effective stimulus than 10 mM MSG. In 3 of these fibers a synergistic effect was recorded to the mixture of GMP and MSG. It is interesting that the response to GMP and MSG was unaffected by gymnemic acid, although it blocked the response to the sweet compounds. Three out of 10 salt fibers responded to MSG and GMP but no synergistic effect was recorded. No specific umami fibers were recorded. However, more data must be collected before the final conclusion on the presence or absence of specific umami fibers can be drawn.