Total Phenolics of Virgin Olive Oils Highly Correlate with the Hydrogen Atom Transfer Mechanism of Antioxidant Capacity

Polar extracts of extra-virgin olive oils (EVOO) contain a large number of phenolic compounds with antioxidant properties. The antioxidant capacity can be measured by different reaction mechanisms, as the single electron transfer (SET) or the hydrogen atom transfer (HAT). In this work, the total phenolic content (TPC) by the Folin-Ciocalteu method and its correlation with four antioxidant capacity assays (FRAP, ABTS, DPPH•and ORAC) were evaluated for EVOO polar extracts. It was observed that the higher the total phenolic compounds in the EVOO extracts, the higher the antioxidant capacities, regardless of the method employed. The reaction mechanism observed for TPC by Folin-Ciocalteu method and also for FRAP, ABTS and DPPH•antioxidant capacity assays is a single electron transfer, thus, a high correlation among their results is expected. However, the correlation between TPC and ORAC results was also high and significant, allowing to conclude that EVOO phenolic compounds are able to react by the hydrogen atom transfer mechanism, which indicates that they can act as effective radical chain-breaking antioxidants. These results suggest that, for the EVOO polar extracts, TPC by Folin-Ciocalteu and ORAC assays could be sufficient to evaluate their in vitro antioxidant capacity.