STUDIES ON MELANOIDIN-TYPE COLORANTS GENERATED FROM THE MAILLARD REACTION OF PROTEIN-BOUND LYSINE AND FURAN-2-CARBOXALDEHYDE - CHEMICAL CHARACTERIZATION OF A RED COLORED DOMAINE

The identification of a coloured substructure of melanoidin-type color ants is reported in the present paper. Brown-orange melanoidins with m ass > 10000 daltons were isolated from a thermally treated aqueous sol ution of casein and furan-2-carboxaldehyde using ultracentrifugation. After complete enzymatic digestion of the protein skeleton, two intens e red coloured compounds were detected in the melanoidin hydrolysate b y HPLC. These compounds were identified as the previously unknown chro mophoric amino acid l-2-(2-furyl)ethenyl]-5-(2-furyl)-2-[(E)-(2-furyl) methylidene]-2,3-dihydro-3-oxo-1H-pyrrol-1-yl} hexanoic acid and its 2-[(Z)-(2-furyl)methylidene] isomer, by using several NMR techniques, by MS, UV, and IR spectroscopy. The identification of these novel comp ounds verifies the idea that melanoidin-type colorants can be generate d by a cross-linking reaction between a low molecular weight chromopho re and a non-coloured high molecular weight biopolymer.