Post-Schiff base chemistry of the Maillard reaction - Mechanism of imine isomerization

Schiff bases play a critical role, not only in initiating the Maillard reaction, but also in its propagation. Little attention has been paid so far to the ability of these imines to undergo isomerization and thus contribute to the diversity of Maillard reaction products. In this study, imine isomerization through 5-oxazolidinone formation was explored in a phenylalanine/glyceraldehyde model system, and spectroscopic evidence was provided for its formation by taking advantage of the strong carbonyl absorption band centered at 1784 cm(-1). The importance of 5-oxazolidinone formation lies in its ability to decarboxylate to azomethine ylide and subsequently form two isomeric imines, each capable of producing distinct Maillard products. Evidence for the formation of such ylides was also provided through their ability to undergo 1,3-dipolar cycloaddition with dipolarophiles.