Identification of blue pigment formed in a D-xylose-glycine reaction system

D-Xylose (1 M), glycine (0.1 M), and sodium hydrogencarbonate (0.1 M) were dissolved in aqueous 60% ethanol at pH 8.1 and left at 26.5°C for 2 days in a dark room under nitrogen displacement. Blue pigment was isolated and purified from the blue solution by anionic exchange and gel filtration chromatographies. Blue pigment which was designated Blue-M1 (blue Maillard reaction intermediate-1) was identified as 5-{[1,4-(dicarboxymethyl)-5-(2,3-dihydroxypropyl)-2-pyrrolo[3,2-b]pyrrolyl]methine}-1,4-(dicarboxymethyl)-2-(1,2,3-trihydroxypropyl)-pyrrolo[3,2-b]pyrroly-lium. Blue-M1 is supposed to be a dimer of yellow colored pyrrolopyrrole-2-carboxaldehyde compounds. Blue-M1 that reacts readily to yellow compounds has a polymerizing activity, suggesting it is an important Maillard reaction intermediate through the formation of melanoidins.