Analyses of the Chemical Structures of Melanoidins by13C NMR,13C and15N CP-MAS NMR Spectrometry

Abstract

Nondialyzable melanoidins, which were prepared from a glucose-glycine system at 95°C for 7, 26 and 44 hr, were subjected to NMR analyses before and after ozonolysis. On 13C CP-MAS NMR, signals in the regions of 10 ~ 50, 60 ~ 75, 105 ~ 115 (I), 130 ~ 140 (II), 170 ~ 180 and 190 ~ 205 (III) ppm were observed for the melanoidins. The signals of I, II and III completely disappeared on ozone-treatment. These findings indicate that the melanoidins were composed mainly of saturated and aliphatic carbons. The 13C NMR spectra of glucose (1-13C)-glycine melanoidins showed that C-1 carbons originating from glucose in the melanoidins were distributed at the positions of aliphatic alkyl methyl (IV), saturated, unsaturated or aromatic and carbonyl (V) carbons. The signals of IV and V disappeared on ozone-treatment. Studies using glycine-2-13C revealed that most of the glycine is incorporated into the melanoidins. On 15N CP-MAS NMR, weak broad signals in the region of 0 ~ 70 ppm and strong signals in the region of 70 ~ ...