3-IMIDAZOL-2-INYL]AZAMETHYLIDENE-1,3-IMIDAZOLIDINE - A NOVEL COLORED SUBSTRUCTURE IN MELANOIDINS FORMED BY MAILLARD REACTIONS OF BOUND ARGININE WITH GLYOXAL AND FURAN-2-CARBOXALDEHYDE

When N-alpha-acetyl-L-arginine was heated with glyoxal in aqueous solu tion at pH 7.0 in the presence of furan-2-carboxaldehyde, an intense r ed-brown color developed. The compound mainly evoking this color was i dentified as )-1-[4-(acetylamino)-4-carboxy-1-butyl]-2-imino-4- -imida zol-2-inyl]}azamethylidene-1,3-imidazolidine (1, BISARG) by applicatio n of several one- and two-dimensional NMR experiments and, in addition , by LC/MSn measurements and UV-vis spectroscopy. This is the first ti me that a chromophoric compound comprising four linked rings with two arginine moieties incorporated was identified in a Maillard reaction s ystem. This novel type of chromophore indicates the possibility that f ood melanoidins might be generated by protein oligomerization via colo red cross-linking structures, for example, between two arginine residu es.