| Abstract
| - Tea catechins may undergo complex reactions such as oxidation, polymerization, and epimerizationduring thermal processing. The thermal stability of tea catechins in an aqueous system, includingdegradation and epimerization reactions, was investigated using a microwave reactor. Reactionswere controlled at high temperatures ranging from 100 to 165 °C with various durations up to 120min. Three sources of tea catechins containing different levels of (−)-epigallocatechin gallate (EGCG),(−)-epicatechin gallate (ECG), and their epimers were studied. Kinetic models for the degradation/epimerization of tea catechins were developed and validated by the reactions at 145 °C. It was shownthat the epimerization and degradation of tea catechins followed first-order reactions and the rateconstants of reaction kinetics followed the Arrhenius equation. Values of the activation energy (Ea)for the epimerization of EGCG from epi- to nonepi-structures, the epimerization of GCG from nonepi-to epi-structures, and the total degradation of EGCG and its epimer GCG were 117.6, 84.2, and 42.8kJ/mol, respectively. For ECG and CG, the Ea values were 119.3, 96.2, and 41.6 kJ/mol, respectively.The mathematical models may provide a useful prediction for the loss of tea catechins during anythermal processing. Keywords: Tea catechins; thermal stability; epimerization; degradation; kinetic model
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