New Guanosine 5’-Phosphate Derivatives as Flavor Enhancers

Umami (the fifth taste) is an essential element in our appreciation of food and is imparted by monosodium L-glutamate (MSG) and 5’-ribonucleotides such as disodium inosine 5’-monophosphate (IMP) and disodium guanosine 5’-monophosphate (GMP). These compounds are now used extensively as seasonings or condiments to supplement, enhance or round off the flavor of many savory-based processed foods. They are the best flavor enhancers that are in commercial use worldwide (Yamaguchi et al. 1998). What is perhaps the most interesting property about MSG and 5’-ribonucleotides is their capacity to interact synergistically. This phenomenon of synergism is of the utmost importance, because it provides an opportunity for the food processor to use less MSG in the formulation without affecting flavor quality. Although a molecular mechanism behind the synergism between MSG and IMP has been recently suggested (Zhang et al. 2008), a number of issues remain to be clarified including the structure/activity relationships (SARs) of 5’-nucleotide-related MSG enhancers. The aim of our current study is to gain further insight into the role played by substituents of the purine nucleus of 5’-ribonucleotides in eliciting a synergism with MSG. In this regard, we synthesized a number of N2-acyl and N2-alkyl guanosine monophosphates, as shown in Scheme 1, and evaluated them for their capacity to enhance the taste intensity of MSG (Cairoli et al. 2008). Using a panel of tasters and the “Probit” method to make the responses of tasters statistically valid, we found that the synergistic activity of some N2-substituted GMPs was significantly higher than that of GMP and was related to the chain length of the alkyl or acyl substituent as well as to the position of a sulphur atom along the carbon chain.