Interfacial Concentrations of Hydroxytyrosol and Its Lipophilic Esters in Intact Olive Oil-in-Water Emulsions: Effects of Antioxidant Hydrophobicity, Surfactant Concentration, and the Oil-to-Water Ratio on the Oxidative Stability of the Emulsions

We determined the interfacial molarities of the antioxidants, AOs, hydroxytyrosol (HT), and HT fatty acid esters with chain lengths of 1 to 16 carbons in intact olive oil/water/Tween 20 emulsions. The results were compared with chain length effects on the oxidative stability of the same emulsions, and a direct correlation was established. Both (AO_I) molarities (varying 50–250 times greater than the stoichiometric 3.5 × 10^–3 M AO concentration) and antioxidant efficiencies show similar parabola-like dependences on AO chain length with a maximum at C₈, consistent with the “cut-off” effect often observed at longer chain lengths. Results should aid in understanding the complex structure–reactivity relationships between AO efficiencies in emulsified systems and their hydrophobilic–hydrophobic balance