Kinetic study of the thermal stability of tea catechins in aqueous systems using a microwave reactor.
Tea catechins may undergo complex reactions such as oxidation, polymerization, and epimerization during thermal processing. The thermal stability of tea catechins in an aqueous system, including degradation and epimerization reactions, was investigated using a microwave reactor. Reactions were controlled at high temperatures ranging from 100 to 165 degrees C with various durations up to 120 min. 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 degrees C. It was shown that the epimerization and degradation of tea catechins followed first-order reactions and the rate constants of reaction kinetics followed the Arrhenius equation. Values of the activation energy (E(a)) 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 42.8 kJ/mol, respectively. For ECG and CG, the E(a) 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 any thermal processing.
Wang
Rong
R
Food Science and Technology Program, Department of Chemistry, National University of Singapore, Singapore.
Zhou
Weibiao
W
Wen
Ruth-Ann Huiyi
RA
D002392:Catechin / Q000031:analogs & derivatives / Q000737:chemistry*; D004355:Drug Stability; D006358:Hot Temperature; D007700:Kinetics; D008872:Microwaves; D012996:Solutions; D013662:Tea / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water
D012996:Solutions; D013662:Tea; D014867:Water; D002392:Catechin; C062669:epicatechin gallate; C045651:epigallocatechin gallate