There is evidence that the same receptors can also bind the ribonucleotides IMP and GMP so causing them to become more sensitive to glutamic acid. This amplifies the response and heightens the pleasure of the experience for the consumer.

This synergy between glutamic acid, IMP and GMP had been documented in 1960 by the Japanese scientist, Kuninaka, many years before the discovery of specific taste receptors. He had carried out experimental sensory work using mixtures of these molecules which showed that the ribonucleotides, although virtually tasteless on their own, amplified the taste effect of glutamic acid considerably. The amplification effect was defined in a formula by another Japanese scientist, Yamaguchi, and is often represented in graphic form as shown below.

Further work by Yamaguchi on palatability has shown clearly that providing sufficient umami impact in savoury foods can help to maintain consumer acceptability when salt levels are reduced. Yeast extracts are able to provide a significant umami effect due to the fact that many of the molecules in yeast are identical to those found in high protein foods such as meat. By digesting these molecules to their basic building blocks, the powerful umami taste is released so that it can be enjoyed in your soup, sauce or meal.