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

α-Tocopherol (α-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 α-tocopherol (50 μM), myricetin (10–250 μM), and their combinations. Taxifolin (TAX) was also tested because it has structural similarities to myricetin but with a higher redox potential. α-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 α-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 α-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 α-tocopherol and through its ability to decrease oxidation by metal chelation.