Synergistic effects of binary mixtures of δ-tocopherol and gallic acid derivatives on peroxidation of soybean oil-in-water emulsions

We employed the antioxidants (+)-δ-tocopherol (TOC), gallic acid (GA), propyl, octyl and lauryl gallates (PG, OG and LG, respectively) and some of their binary combinations (TOC + GA derivative) to evaluate potential synergistic, additive or antagonistic effects in inhibiting the lipid peroxidation in soybean oil-in-water emulsions. For the purpose, we added to the prepared emulsions individual antioxidants or binary TOC/co-antioxidant mixtures of different [TOC]/[co-antioxidant] ratios and carried out two sets of independent experiments. In the first one, we determined the relative efficiency of the antioxidants and their mixtures by monitoring the oxidation kinetics of the emulsions. In the second set of experiments, we determined, in the same intact emulsions, their effective concentrations in the oil, aqueous and interfacial regions. When binary TOC-co-antioxidant mixtures were employed, synergistic effects were detected except when the mixture contained low concentrations of gallic acid, in this case an additive effect was observed. Overall, results suggest that the effective interfacial concentrations of the antioxidants and/or their mixtures can be a critical parameter to correctly interpret the observed variations in antioxidant efficiencies but not the only one because the rate constants of the various processes may have also a relevant role in determining their relative rates.