Identification of red pigments formed in a D-xylose-glycine reaction system

Blue, red, and yellow pigments were formed in the D-xylose (1 M)-glycine (0.1 M) reaction system. Novel red pigments were isolated and purified from the reaction solution, designated Red-M1 (red Maillard intermediate-1) and Red-M2 (red Maillard intermediate-2). Red-M1 was identified as 1,4,6,9-tetracarboxymethyl-5-(1,2,3,4-tetrahydroxybutyl)-8-hydroxymethyl-3-(2,3-dihydroxypropyl)-5,6-dihydro-pyrrolo[2',3':4,5]pyrrolo[2,3-e]pyrrolo[3,2-b]azepine-9-ium. NMR and CD data indicated that Red-M2 was a diastereomer of Red-M1. They are assumed to be important Maillard reaction intermediates through the formation of melanoidins as well as blue pigments.