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

Rong Wang, Weibiao Zhou* and Xiaohui Jiang

Food Science and Technology Programme, Department of Chemistry, National University of Singapore, Science Drive 4, Singapore 117543

J. Agric. Food Chem., 2008, 56 (8), pp 2694–2701

DOI: 10.1021/jf0730338

Publication Date (Web): March 25, 2008

* Author to whom correspondence should be addressed. Telephone: (65) 6516-3501 . Fax: (65) 6775-7895. E-mail: chmzwb@nus.edu.sg.

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.

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