Stabilization of foam and emulsion by subcritical water-treated soy protein: Effect of aggregation state

Abstract

Soy protein isolate (SPI, 1–4 wt%) was heated by conventional heat treatment (90 °C) and subcritical water treatment (SW, 120 °C). The aggregation degree, surface hydrophobicity, interfacial adsorption behaviors, foaming and emulsifying properties were characterized to evaluate the effects of aggregation degree on the foaming and emulsifying properties of proteins. SW treatment induced the formation of larger soluble aggregates dominated by intermolecular hydrophobic interactions. Compared to native SPI and SPI heated at 90 °C (SPI90), SW-treated SPI showed a higher surface activity at the air-water and oil-water interface due to lower aggregation degree and more flexible conformation. Obvious improvements of foam capacity and stability may be attributed to the formation of an interfacial layer with higher macromolecule interactions. Moreover, SW treatment effectively improved storage and freeze-thaw stability against emulsion coalescence due to the formation of a thicker multilayer, although higher flocculation degree was observed. These results suggest that SW treatment could be an effective technique to modify structural and functional properties of soy protein for stable foam and emulsion foods.