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)-N²-(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 C₆-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)-N²-(1-carboxyalkyl)-guanosine 5′-monophosphates and (R)- and (S)-N²-(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 N²-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.