Distribution of hydroxytyrosol and hydroxytyrosol acetate in olive oil emulsions and their antioxidant efficiency

We employed a kinetic method to determine the distributions of the antioxidants hydroxytyrosol (HT) and hydroxytyrosol acetate (HTA) between the oil, aqueous, and interfacial regions of a model food emulsion composed of stripped olive oil, acidic water, and a blend of Tween 80 and Span 80 [hydrophilic–lipophilic balance (HLB) = 8.05] as an emulsifier. HT is oil-insoluble, but HTA is both oil- and water-soluble (partition constant P(O)(W) = 0.61). Results indicate that, at a given emulsifier volume fraction Φ(I), the fraction of HTA in the interfacial region is higher than that of HT. The percentage of both antioxidants increases with an increasing Φ(I), so that % HT > 40% at Φ(I) = 0.005 and % HT > 80% at Φ(I) = 0.04. HTA appears to be a better antioxidant than HT, as shown by an accelerated oxidative test (Schaal oven method). A correlation between their distribution in the emulsion and their efficiency was established.