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 formation (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 reaction were determined in a phenylalanine-glucose system to elucidate its early-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 rearrangement, 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 Amadori rearrangement was more sensitive to temperature changes and was more favorable at higher temperatures. These suggested that the chemical nature of the reactants, determined by their structures and pH condition, is more important to control the reaction. These results were also supported by the pH and temperature profiles of the Amadori compound formation.