Antioxidant activity of green tea polyphenols against lipid peroxidation initiated by lipid-soluble radicals in micelles

Abstract

Antioxidant effects of the principal polyphenolic components extracted from green tea leaves, i.e., (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCG), against peroxidation of linoleic acid have been studied in sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) micelles. The peroxidation was initiated thermally by a lipid-soluble azo initiator di-tert-butyl hyponitrite (DBHN) and the reaction kinetics were followed by formation of linoleic acid hydroperoxides and consumption of the antioxidant. Kinetic analysis of the antioxidation process demonstrates that these green tea polyphenols are effective antioxidants in micelles used either alone or in combination with α-tocopherol (vitamin E), but their antioxidative behaviour and relative effectiveness are substantially different from those in the water-soluble initiator AMPAD-initiated peroxidations reported previously. The antioxidative action of the green tea polyphenols (GOHs) in DBHN-initiated peroxidation involves trapping the initiating tert-butoxyl radical and the propagating linoleic acid peroxyl radicals. However, the GOHs could not participate in the α-tocopherol recycling reaction as in the case of AMPAD-initiated reactions due to their very fast reaction with the initiating tert-butoxyl radical.