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Comparison of antioxidant activity and bioavailability of tea epicatechins with their epimers

Published online by Cambridge University Press:  09 March 2007

Jin Ze Xu ,
Sai Ying Venus Yeung ,
Qi Chang ,
Yu Huang  and
Zhen-Yu Chen
Jin Ze Xu
Affiliation:
Food and Nutritional Sciences Programme, Department of Biochemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
Sai Ying Venus Yeung
Affiliation:
Food and Nutritional Sciences Programme, Department of Biochemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
Qi Chang
Affiliation:
Department of Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
Yu Huang
Affiliation:
Department of Physiology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
Zhen-Yu Chen*
Affiliation:
Food and Nutritional Sciences Programme, Department of Biochemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
*
*Corresponding author: Dr Zhen-Yu Chen, fax +852 26037246, email [email protected]
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Abstract

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Canned and bottled tea drinks contain not only green tea epicatechins (GTE), namely (−)-epigallocatechin gallate (EGCG), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epicatechin (EC), but also four GTE epimers, namely (−)-gallocatechin gallate (GCG), (−)-catechin gallate (CG), (−)-gallocatechin (GC) and (−)-catechin (C). In the present study we examined the antioxidant activity and bioavailability of these epimers compared with their corresponding precursors. The epimerisation reaction was induced by autoclaving GTE extract derived from longjing green tea at 120°C for 20 min. Isolation and purification of each GTE and epimer were accomplished by various column chromatographic and semi-preparative HPLC techniques. The antioxidant activity of each epimer with its corresponding GTE precursor was conducted in the three in vitro systems, namely human LDL oxidation, ferric reducing–antioxidant power (FRAP), and anti-2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical assays. The results of all three assays demonstrated that CG had similar antioxidant activity with its precursor ECG, while GC was less potent as an antioxidant than its precursor EGC. Regarding EGCG and GCG, the antioxidant potency was similar for both LDL oxidation and DPPH free radical assays, but GCG was statistically less effective than EGCG in the FRAP assay. For EC and C, the latter had less anti-free radical activity in the DPPH assay, but in LDL oxidation and FRAP assays the antioxidant activity was similar. Oral and intravenous dosing of GTE–epimer mixture led to increase in total plasma antioxidant capacity in rats. In general, both epicatechins and epimers had low bioavailability (0·08–0·31) and most of the observed differences between epicatechins and their corresponding epimers were small, even if they were statistically significant in some cases. It was concluded that the epimerisation reaction occurring in manufacturing canned and bottled tea drinks would not significantly affect antioxidant activity and bioavailability of total tea polyphenols.

Keywords

CatechinEpicatechinEpigallocatechinEpimerisationGallocatechinTea drinks
Type
Research Article
Information
British Journal of Nutrition , Volume 91 , Issue 6 , June 2004 , pp. 873 - 881
Copyright
Copyright © The Nutrition Society 2004

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