Nonenzymatic browning reactions of retro-aldol degradation products of carbohydrates

Methylglyoxal and glyceraldehyde were used to demonstrate the involvement of retro-aldol degradation products of carbohydrates in browning (A(420)), the formation of hydroxymethylfurfural (HMF), and the extent to which the mechanism of browning proceeds by homolytic or heterolytic pathways in the caramelization and Maillard reactions of mono- and disaccharides. The amino component of Maillard systems is required for the retro-aldol cleavage of D-glucose. The short-chain alpha-dicarbonyl compounds so formed appear to dominate not only the formation of brown products but also the mechanism of the browning of D-glucose under these conditions, even if only small amounts are formed. Evidence is presented to link the formation of free radicals in the browning of glucose to reactions of the retro-aldol products. A novel reaction pathway is suggested for the formation of HMF from glyceraldehyde.