Mafalda Meireles1, Sonia Losada-Barreiro1,2, Marlene Costa1, Fátima Paiva-Martins1, Carlos Bravo-Díaz2, Luís S Monteiro3. 1. REQUIMTE-LAQV, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Porto, Portugal. 2. Department of Physical Chemistry, Faculty of Chemistry, University of Vigo, Vigo, Spain. 3. Department of Chemistry, University of Minho, Campus de Gualtar, Braga, Portugal.
Abstract
BACKGROUND: Controlling the interfacial concentrations of antioxidants (AOs) in oil-in-water emulsions can be regarded as a unique approach for increasing the efficiency of AOs in inhibiting the oxidation of lipids. Classical methods to determine the AO distribution in binary systems cannot be employed and their distribution needs to be assessed in the intact emulsion. RESULTS: We have employed a well-established kinetic method to determine the distribution of a homologous series of AOs derived of chlorogenic acid in olive oil-in-water emulsions and analyse the effects of AO hydrophobicity on their distributions and their efficiencies. Results indicate that variations in the efficiency of chlorogenates in emulsions are due to differences in their interfacial concentrations. Their interfacial concentrations AOI were much higher (20- to 150-fold) than their stoichiometric concentrations. On the other hand, their concentrations in the oil region were 1.5- to 0.1-fold. Results also show the complex effect of the oil-to-water ratio employed in the preparation of the emulsions on the (AOI ) values. CONCLUSION: Results highlight the key role of the interfacial region and of its composition (interfacial AO molarity, emulsifier concentration, oil-to-water ratio) in interpreting the efficiency of AOs in inhibiting lipid oxidation in emulsions. Thus, a careful modulation of these parameters is necessary to ensure optimum AO efficiency.
BACKGROUND: Controlling the interfacial concentrations of antioxidants (AOs) in oil-in-water emulsions can be regarded as a unique approach for increasing the efficiency of AOs in inhibiting the oxidation of lipids. Classical methods to determine the AO distribution in binary systems cannot be employed and their distribution needs to be assessed in the intact emulsion. RESULTS: We have employed a well-established kinetic method to determine the distribution of a homologous series of AOs derived of chlorogenic acid in oliveoil-in-water emulsions and analyse the effects of AO hydrophobicity on their distributions and their efficiencies. Results indicate that variations in the efficiency of chlorogenates in emulsions are due to differences in their interfacial concentrations. Their interfacial concentrations AOI were much higher (20- to 150-fold) than their stoichiometric concentrations. On the other hand, their concentrations in the oil region were 1.5- to 0.1-fold. Results also show the complex effect of the oil-to-water ratio employed in the preparation of the emulsions on the (AOI ) values. CONCLUSION: Results highlight the key role of the interfacial region and of its composition (interfacial AO molarity, emulsifier concentration, oil-to-water ratio) in interpreting the efficiency of AOs in inhibiting lipid oxidation in emulsions. Thus, a careful modulation of these parameters is necessary to ensure optimum AO efficiency.