Effects of purine and pyrimidine 5′-ribonucleotides on glutamate detection threshold and umami intensity in Japanese young female trained participants

Umami taste of L-glutamate can be synergistically amplified by the addition of some purine 5'-ribonucleotides, most notably inosine 5'-monophosphate and guanosine 5'-monophosphate (GMP). However, potential synergistic effects of other 5'-ribonucleotides, such as adenosine 5'-monophosphate (AMP), cytidine 5'-monophosphate (CMP), and uridine 5'-monophosphate (UMP), have not been well characterized. Most recently, CMP has been proposed to function as a negative modulator of glutamate taste in some US participants. Here, we examined the effects of mixing these five 5'-ribonucleotides with monopotassium L-glutamate (MPG) on MPG detection threshold and umami intensity using Japanese young female trained participants. Purine 5'-ribonucleotides (IMP, GMP, AMP) significantly decreased MPG detection threshold and enhanced umami taste intensity. UMP showed a weak but significant reduction of MPG detection threshold and a slight but significant enhancement of umami intensity. CMP, however, did not modify MPG detection threshold or umami intensity. The rank order of the effects was GMP ≧IMP > AMP > UMP. Therefore, these results did not support the hypothesis that "CMP functions as a negative modulator of glutamate taste", at least in the Japanese young female trained participants.