Monitoring of the Maillard Reaction Based on the Reduction of Tetrazolium Salt XTT

The reduction of tetrazolium XTT with the Maillard reaction system containing various sugars or aldehydes and glycine was monitored and compared with the conventional indices of the Maillard reaction such as nitroblue tetrazolium (NBT) and dichlorophenolindophenol (DPI) reducibility, free hydroxymethylfurfural and browning. The change in XTT reducibility against the monosaccharide-glycine system showed a similar behavior as that of NBT and DPI reducibility, indicating that the Amadori product and reductones formed in the Maillard reaction may be involved in the reduction of XTT. In contrast, the XTT reducibility against the disaccharide-glycine system consisting of lactose, lactulose or cellobiose showed a different behavior from those indices. In the system, the reduction of XTT was caused by the substances which have a low reducibility of NBT. Such a property was recognized in some model systems, including the condensation reaction of D-glucosamine, that can form nitrogen-containing heterocyclic compounds such as pyrazinium and pyridinium. The condensation product of D-glucosamine rapidly lost the XTT reducibility with the addition of Cu2+. The phenomenon was also observed in the UHT-treated milk, and the decrease in the XTT reducibility during the storage was suggested to be due to the presence of Cu2+ in milk.