Influence of concentration ratio on emulsifying properties of Quillaja saponin - protein or lecithin mixed systems

Abstract

The concentration ratio of binary surfactant systems can alter the interfacial layer properties, and consequently affect emulsion stability. To study the effect of varying concentration ratios (r, % w/w) of interfaces containing Quillaja saponins and other naturally occurring food-grade surfactants on their emulsifying properties, we evaluated particle size, ζ-potential, and appearance of 10% oil-in-water emulsions (pH 7) stabilized by Quillaja saponin - protein or Quillaja saponin - lecithin mixtures. Quillaja saponin - Na-caseinate mixtures (r = 0.3:0.2, 0.2:0.3, and 0.1:0.4) formed small emulsion droplets (d43: 0.2 – 0.3 μm), whereas at r = 0.4:0.1, the emulsions contained micron-sized droplets (d43: 1.217 ± 0.558 μm). Emulsions formed by Quillaja saponin - pea protein mixtures flocculated at r = 0.3:2.0, 0.2:3.0, and 0.1:4.0. In contrast, Quillaja saponin - rapeseed lecithin or egg lecithin mixtures were able to generate small emulsion droplets (d43: 0.2 – 0.5 μm) at all tested concentration ratios. The formation of stable emulsions using binary mixtures of naturally occurring emulsifiers was more dependent on the concentration ratio of the proteins than lecithins, indicating that the interfacial behavior of Quillaja saponins is more sensitive to the presence of proteins. This was attributed to attractive molecular interactions yielding complexes at interfaces and/or in the continuous phase. This study shows that food-grade binary surfactant mixtures can be used to form stable emulsions with properties being tunable by altering the mixing ratios between surfactants.