Pentoses and Hexoses as Sources of New Melanoidin-like Maillard Polymers

N-Substituted pyrroles (1), 2-furaldehyde (2), and N-substituted 2-formylpyrroles (3), formed in pentose (hexose) Maillard systems, were identified as components of extraordinary polycondensation activity. The polycondensation was studied in model experiments with N-methylpyrrole (1a)/N-methyl-2-formylpyrrole (3a), N-(2-methoxycarbonylethyl)pyrrole (1b)/N-(2-methoxycarbonylethyl)-2-formylpyrrole (3b), N-methyl-2-formylpyrrole (3a), N-methylpyrrole (1a)/2-furaldehyde (2), and N-(2-methoxycarbonylethyl)pyrrole (1b)/2-furaldehyde (2), respectively. MALDI-TOF-MS spectra indicated regular oligomers of up to 15-30 methine-bridged N-methyl(or N-2-methoxycarbonylethyl)-pyrroles. With participation of aldehyde 2, furan rings instead of pyrrole rings were incorporated. The oligomers 5-11 were isolated and identified by MS and NMR techniques. A complementary experiment with N-methyl-2-[¹³C]formylpyrrole ([¹³CHO]-3a)/N-methylpyrrole (1a) was performed. The relevance of the new (type II) melanoidin-like oligomers/polymers in Maillard reactions is discussed and, in conclusion, a corresponding structure for native melanoidins is proposed. The oligomers 5, 6, 8, and 9 were tested for antioxidative activity in an iron(III) thiocyanate assay.