15 May 2015
Food Chemistry. 175, pp. 233 - 242.
Marlene Costaa, Sonia Losada-Barreiroab, Fátima Paiva-Martinsa, Carlos Bravo-Díaz*b, Laurence S. Romstedc
Autor affilations:
*Corresponding authors
aREQUIMTE-LAQV, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007, Portugal
bDpt. Química Física, Facultad de Química, Universidad de Vigo, Vigo-Pontevedra, Spain
cDepartment of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854, United States
E-mail: cbravo@uvigo.es
Abstract
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, PO(I), show a maximum at the C8 ester. A reaction between caffeic acid, CA, and its specially synthesised C1-C16 alkyl esters, and a chemical probe is used to estimate partition constants for AO distributions and interfacial rate constants, kI, 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, ΦI=0.005.