Abstract: The purpose of this study was to explore the effect of the ratio and interaction between soybean protein isolate and lecithin on the stability and functional properties of emulsion systems containing them. The results showed that emulsion activity index and droplet size distribution were affected by the ratio between soybean protein isolate and lecithin. When the ratio was 10:1, a higher emulsion activity index (98.1 m2/g) and the smallest D4,3 (volume average diameter, 13.34 μm) as well as a lower level of bimodal distribution were observed. A soybean protein isolate-to-lecithin ratio of 1:1 or 100:1 was not suitable due to poor emulsion stability, as demonstrated by the measurement of ζ-potential. Phase separation and large irregular non-spherical droplets were evident under confocal laser scanning microscopy. Therefore, there was an optimal soybean protein isolate-to-lecithin ratio that provided good stability of food-grade O/W emulsion.

Key words: soybean protein isolate, lecithin, protein-lecithin interaction, emulsion stability