Reaction Kinetics of Degradation and Epimerization of Epigallocatechin Gallate (EGCG) in Aqueous System over a Wide Temperature Range

(–)-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.