Systematic Studies on the Chemical Structure and Umami Enhancing Activity of Maillard-Modified Guanosine 5'-Monophosphates

摘要

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 Maiilard-type model reactions were performed with 5'-GMP and a homologous series of monosaccharides exhibiting a C3- 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-carbbxyalkyl)-guanosine 5'-monophosphates and (R)- and (S)-N~2-(1-alkylamino)carbonylalkyl)guanosine 5'-mono-phosphates 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.