Reaction kinetics of degradation and epimerization of epigallocatechin gallate (EGCG) in aqueous system over a wide temperature range

Abstract

(-)-Epigallocatechin gallate (EGCG) is the most abundant catechin in green tea, which has been linked with many health benefits. To ensure the conceivable health benefits from thermally processed products, a kinetic study on the stability of (-)-EGCG in aqueous system was carried out using a HPLC-UV system and Matlab programming. Simultaneous degradation and epimerization of (-)-EGCG were characterized during isothermal reactions at low temperatures (25-100°C) combined with previously conducted experimental results at high temperature (100-165°C); the degradation and epimerization complied with first-order reaction and their rate constants followed Arrhenius equation. Mathematical models for the stability of (-)-EGCG were established and validated by the reactions at 70°C and with varied concentrations from different catechin sources. Two specific temperature points in the reaction kinetics were identified, at 44 and 98°C, respectively. Below 44°C, the degradation was more profound. Above 44°C, the epimerization from (-)-gallocatechin gallate (GCG) to (-)-EGCG was faster than degradation. When temperature increased to 98°C and above, the epimerization from (-)-GCG to (-)-EGCG became prominent. Our results also indicated that the turning point of 82°C reported in the literature for the reaction kinetics of catechins would need to be re-examined. © 2008 American Chemical Society.