KINETIC SIGNIFICANCE OF THE SCHIFF-BASE REVERSION IN THE EARLY-STAGE MAILLARD REACTION OF A PHENYLALANINE-GLUCOSE AQUEOUS MODEL SYSTEM

The kinetic constants (k) and activation energy (E-a) for the formatio n (k(1), E-a1) and reversion (k(-1), Ea-1) of the Schiff base complex and for the Amadori rearrangement (k(2), E-a2) of the Maillard reactio n were determined in a phenylalanine-glucose system to elucidate its e arly-stage mechanism. The k(-1) and k(2) were 10(3) times greater than the k(1), indicating the Schiff base formation, but not the Amadori r earrangement, was the rate-limiting step of the reaction. The E-a2 (8. 01 x 10(4) kcal/mol) was slightly greater than the E-a1 (6.52 x 10(4) kcal/mol) and the Ea-1 (7.49 x 10(4) kcal/mol), revealing that the Ama dori rearrangement was more sensitive to temperature changes and was m ore favorable at higher temperatures. These suggested that the chemica l nature of the reactants, determined by their structures and pH condi tion, is more important to control the reaction. These results were al so supported by the pH and temperature profiles of the Amadori compoun d formation.