Analysis of the mechanism of antioxidant synergism between -tocopherol and myricetin in bulk oil

alpha-Tocopherol (alpha-TOC) and myricetin (MYR) synergistically inhibit lipid oxidation in bulk oil but the mechanism underlying this effect is unknown. In this research, stripped soybean oil (SSO) was treated with alpha-tocopherol (50 mu M), myricetin (10-250 mu M), and their combinations. Taxifolin (TAX) was also tested because it has structural similarities to myricetin but with a higher redox potential. alpha-Tocopherol: myricetin ratios of 5:1, 2:1, 1:1, 1:2, and 1:5 resulted in extended lag phases ranging from 16 to 99 days, with lag phase increasing with increasing myricetin concentrations. Synergism between alpha-tocopherol and myricetin was also observed in phospholipid-containing bulk oils both in the absence and presence of reverse micelles, although the reverse micelles shortened the lag phases. Myricetin (redox potential = 360 mV) delayed the oxidation of alpha-tocopherol (redox potential = 500 mV) whereas taxifolin (redox potential = 500 mV) did not. Both myricetin and taxifolin were able to chelate iron as determined by UV-VIS spectroscopy. These results suggested that the lower redox potential of myricetin allowed it to produce synergistic antioxidant activity potentially by regenerating oxidized alpha-tocopherol and through its ability to decrease oxidation by metal chelation.