Abstract
In order to reveal the mechanism of the Maillard reaction between proteins and reducing sugars, unmodified and chemically modified lysozymes were incubated with and without glucose at 50°C and 75% relative humidity in the solid state. Incubation of unmodified lysozyme with glucose resulted in browning and polymerization of the protein, and noticeable losses of arginine, lysine, and tryptophan residues. Those changes were little affected by the presence of an oxygen adsorber. Acetylation of lysozyme almost completely prevented those changes, indicating that the reaction of free amino groups of the protein with glucose is essential at the initial stage of these changes.
Incubation of lysozyme the arginine residues of which were maskedwith 1, 2-cyclohexanedione (CHD)resulted in almost the same changes as above even in the absence of glucose. Those changes could be explained as caused by the action of CHD released from the arginine residues. This similarity in the effects on protein of CHD and glucose implies that dicarbonyl compounds are key components at the secondary stage of the Maillard reaction between proteins and reducing sugars.
