Composition of Quillaja saponin extract affects lipid oxidation in oil-in-water emulsions.

Quillaja saponin extract comprises both, surfactants and phenolic compounds, which makes it interesting, in particular, for the formulation of sensitive functional food ingredients and its protection against oxidation. The aim of this study was to investigate the antioxidant effect of Quillaja saponin extract in oil/water emulsions. Emulsions stabilised by Quillaja saponin showed decreased oxidation stability due to naturally occurring metals but stability increased to a great extent when a chelating agent was added. Antioxidant efficiency of the saponin extract was determined photometrically by 2,2'-diphenyl-1-picrylhydrazyl (DPPH) assay and by the use of electron paramagnetic resonance spectroscopy (EPR). EPR spectroscopy applying stable hydrophilic and hydrophobic radicals is advantageous, especially for characterisation of antioxidant efficiency at the interface. The extract showed antioxidant activity towards radicals in both environments, aqueous and hydrophobic, indicating the importance of phenolic compounds for the antioxidant properties of Quillaja saponin extract and their presence at the interface facilitated by saponin molecules.