Interfacial Behavior and Antioxidant Efficiency of Olive Phenolic Compounds in O/W Olive oil Emulsions as Affected by Surface Active Agent Type

The aim of this study was to evaluate the interfacial behavior of syringic acid, tyrosol and oleuropein, phenolic antioxidant compounds naturally present in olives and olive oils, and their ability to influence the stability to lipid oxidation of olive oil O/W emulsions. To test also the interactions of these molecules with other components and the effects on their activity, two different surfactants were used to prepare the olive oil emulsions, Tween 20, and a whey protein concentrate (WPC). All the antioxidants affected the olive oil/water interfacial tension; among them, oleuropein showed the highest interfacial activity and, thus, is supposed to locate at the interface. In emulsified state, the presence of the phenolic compounds in WPC emulsions did not cause any significant effect on the dispersion degree if compared to the control whilst a general improvement was observed in Tween 20-emulsions, in particular when oleuropein was added systems. The antioxidants were thus proven not to impair the dispersed structure but rather to improve it. As regards the oxidative stability, the antioxidants under investigation caused the occurrence of similar induction phases in the hydroperoxides production not observed in the control emulsions. In the case of secondary oxidation products, the highest inhibition was achieved in both the emulsified systems by oleuropein. In general, however, a lower amount of both primary and secondary oxidation products were observed in WPC emulsions than in Tween 20-emulsions likely due to the antioxidative effect of whey proteins.