Systematic studies on the chemical structure and umami enhancing activity of Maillard-modified guanosine 5'-monophosphates

Recent investigations on taste active principles in nucleotide rich yeast extracts led to the discovery of (R)- and (S)-N(2)-(1-carboxyethyl)-guanosine 5'-monophosphate as previously not reported umami enhancing molecules formed upon the Maillard reaction of guanosine 5'-monophosphate (5'-GMP) with dihydroxyacetone and glyceraldehyde, respectively. In the present study, systematic Maillard-type model reactions were performed with 5'-GMP and a homologous series of monosaccharides exhibiting a C(3)- to C(6)-carbon skeleton as well as with the reducing disaccharide maltose in the presence of an amino acid. By preparative RP-HPLC, various (R)- and (S)-N(2)-(1-carboxyalkyl)-guanosine 5'-monophosphates and (R)- and (S)-N(2)-(1-alkylamino)carbonylalkyl)guanosine 5'-monophosphates were isolated and identified by means of LC-MS, LC-TOF-MS, and 1D/2D-NMR spectroscopy. Sensory evaluation of these Maillard products revealed β-values for umami enhancement between 0.06 and 7.0 and identified a strong influence of the stereochemistry as well as the chain length of the N(2)-substituent on the umami enhancing activity. For all of the compounds evaluated, the (S)-configured isomers showed higher taste impact, whereas the (R)-isomers showed only marginal β-values, thus underlining the stereospecifity of the umami taste receptor binding site.