R. Tressl et al., PENTOSES AND HEXOSES AS SOURCES OF NEW MELANOIDIN-LIKE MAILLARD POLYMERS, Journal of agricultural and food chemistry, 46(5), 1998, pp. 1765-1776
N-Substituted pyrroles (1), 2-furaldehyde (2), and N-substituted 2-for
mylpyrroles (3), formed in pentose (hexose) Maillard systems, were ide
ntified 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-form
ylpyrrole (3a), N-methylpyrrole (1a)/2-furaldehyde (2), and N-(2-metho
xycarbonylethyl)pyrrole (1b)/2-furaldehyde (2), respectively. MALDI-TO
F-MS spectra indicated regular oligomers of up to 15-30 methine-bridge
d N-methyl(or N-2-methoxycarbonylethyl)-pyrroles. With participation o
f aldehyde 2, furan rings instead of pyrrole rings were incorporated.
The oligomers 5-11 were isolated and identified by MS and NMR techniqu
es. A complementary experiment with N-methyl-2-[C-13]formylpyrrole ([(
CHO)-C-13]-3a)/N-methylpyrrole (1a) was performed. The relevance of th
e new (type II) melanoidin-like oligomers/polymers in Maillard reactio
ns is discussed and, in conclusion, a corresponding structure for nati
ve melanoidins is proposed. The oligomers 5, 6, 8, and 9 were tested f
or antioxidative activity in an iron(III) thiocyanate assay.