Abstract

Antioxidative effects of the main polyphenolic components extracted from green tea leaves, i.e. (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin gallate (EGCG) and gallic acid (GA), against free radical initiated peroxidation of human low density lipoprotein (LDL) were studied. The peroxidation was initiated either thermally by a water-soluble initiator 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH), or photochemically by a triplet sensitizer benzophenone (BP). The reaction kinetics was monitored by the uptake of oxygen and the depletion of α-tocopherol (TOH) presented in the native LDL. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants against both AAPH-initiated and BP-photosensitized LDL peroxidation. The antioxidative action of the green tea polyphenols includes trapping the initiating and/or propagating peroxyl radicals with the activity sequence EC>EGCG>ECG>EGC>GA for the AAPH initiated peroxidation, and reducing the α-tocopheroxyl radical to regenerate α-tocopherol with the activity sequence of ECG>EC>EGCG>EGC>GA and ECG>EGCG>GA>EC>EGC for the AAPH-initiated and BP-photosensitized peroxidations respectively.

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