What is the influence of a phenolic compound in the antioxidant capacity of other one: synergistic effect?

Virgin olive oil has a high resistance to oxidative deterioration due to its tryacylglycerol composition low in polyunsaturated fatty acids and to the presence of a group of phenolic antioxidants composed mainly of polyphenols and tocopherols. When several phenolic compounds of extra-virgin olive oil (phenylethyl alcohols, lignans and secoiridoids) are isolated and their antioxidant capacity is evaluated by measuring the radical scavenging effect (DPPH test), by OSI test and by an electrochemical method, it is possible to verify that, as is generally assumed, the presence of a single hydroxyl group confers a limited amount of antioxidant activity. Furthermore, the presence of an odiphenol enhances the ability of the phenolic compounds to act as antioxidants. The results obtained for the three tests show that hydroxytyrosol,deacetoxy oleuropein aglycon and oleuropein aglycon are the strongest in the classification in terms of antioxidant power. Furthermore, it is very interesting to observe the results obtained for the OSI test, where several of the compounds under study showed antioxidant activity, and the others showed pro-oxidant effects. Considerable evidence has been gathered on the synergistic effects of various compounds in lipids, so it would be very interesting to check the effect of carry out the OSI test adding to a glyceridic matrix without phenolic compounds a mixture of two phenols. In this work, we summarize the results previously mentioned and also comment the synergistic effect that exists between hydroxytyrosol and tyrosol (one of them, hydroxytyrosol, was the analyte which was found to exert the strongest antioxidant activity in the OSI test; and the other, tyrosol, was one of the compounds that exhibited a high pro-oxidant influence in the same test). We put together these two compounds and evaluated their effect in a triolein matrix by OSI test.