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-[ 13 C]formylpyrrole ([ 13 CHO]- 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. Keywords: Model compounds for melanoidins; pyrroles from pentoses and hexoses; β-dicarbonyl pathway of the Maillard reaction; polycondensation of N -methylpyrrole with N -methyl-2-formylpyrrole ( N -methyl-2-[ 13 C]formylpyrrole) or 2-formylfuran; polycondensation of N -(2-methoxycarbonylethyl)pyrrole with N -(2-methoxycarbonylethyl)-2-formylpyrrole or 2-formylfuran; MALDI-TOF-MS analysis of melanoidin-like oligomers/polymers; antioxidative activity of oligomeric model compounds