A direct correlation between the antioxidant efficiencies of caffeic acid and its alkyl esters and their concentrations in the interfacial region of olive oil emulsions. The pseudophase model interpretation of the cut-off effect

Recently published results for a series of homologous antioxidants, AOs, of increasing alkyl chain length show a maximum in AO efficiency followed by a significant decrease for the more hydrophobic AOs, typically called the cut-off' effect. Here we demonstrate that in olive oil emulsions both antioxidant efficiencies and partition constants for distributions of AOs between the oil and interfacial regions, P-O(I), show a maximum at the C-8 ester. A reaction between caffeic acid, CA, and its specially synthesised C-1-C-16 alkyl esters, and a chemical probe is used to estimate partition constants for AO distributions and interfacial rate constants, k(I), in intact emulsions based on the pseudophase kinetic model. The model provides a natural interpretation for both the maximum and the cut-off' effect. More than 70% of the CA esters are in the interfacial region even at low surfactant volume fraction, Phi(I) = 0.005. (c) 2014 Elsevier Ltd. All rights reserved.