Antioxidant synergism of tea polyphenols and α-tocopherol against free radical induced peroxidation of linoleic acid in solution

Abstract

Peroxidation of linoleic acid was initiated by a water soluble azo initiator 2,2′-azo(2-amidinopropane)dihydrochloride (AAPH) in tert-butyl alcohol–water solution and inhibited by α-tocopherol and polyphenols extracted from green tea, i.e. (–)-epicatechin (EC), (–)-epigallocatechin (EGC), (–)-epicatechin gallate (ECG), (–)-epigallocatechin gallate (EGCG) and gallic acid (GA), either alone or in combination. The reaction kinetics were followed by oxygen uptake, formation of linoleic acid hydroperoxides and consumption of the antioxidants. It was found that the tea polyphenols could slow the rate of peroxidation with an activity sequence of EGCG > EGC ≈ ECG > EC ≈ GA, but no definite inhibition period was observed. On the other hand, the tea polyphenols could significantly increase the inhibition period of α-tocopherol and protect the latter from depletion with an activity sequence of EGCG ECG ≈ EGC > GA > EC when they were used in combination. A synergistic antioxidation mechanism involving the recycling of α-tocopherol by the tea polyphenol is proposed.