title: 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.
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.
authors.affiliation: CIQ-UP, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007, Portugal.
authors.forename: Marlene
authors.initials: M
authors.lastname: Costa
authors.affiliation: CIQ-UP, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007, Portugal; Universidad de Vigo, Fac. Química, Dpto Química Física, 36200 Vigo, Spain.
authors.forename: Sonia
authors.initials: S
authors.lastname: Losada-Barreiro
authors.affiliation: CIQ-UP, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, 4169-007, Portugal. Electronic address: mpmartin@fc.up.pt.
authors.forename: Fátima
authors.initials: F
authors.lastname: Paiva-Martins
authors.affiliation: Universidad de Vigo, Fac. Química, Dpto Química Física, 36200 Vigo, Spain. Electronic address: cbravo@uvigo.es.
authors.forename: Carlos
authors.initials: C
authors.lastname: Bravo-Díaz
authors.affiliation: Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, NJ 08854, USA.
authors.forename: Laurence S
authors.initials: LS
authors.lastname: Romsted
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D002109:Caffeic Acids / Q000737:chemistry*; D004655:Emulsions / Q000737:chemistry; D004952:Esters / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D000069463:Olive Oil; D010938:Plant Oils / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D000975:Antioxidants; D002109:Caffeic Acids; D004655:Emulsions; D004952:Esters; D000069463:Olive Oil; D010938:Plant Oils; D013501:Surface-Active Agents; C040048:caffeic acid
keywords: Antioxidant distributions; Antioxidants; Caffeic acid alkyl esters; Cut-off effect; Emulsions; Partition constants; Pseudophase kinetic model