Abstract: The purpose of this study was to explore the effect of ultrasonic treatment on the properties of O/W emulsion containing soybean protein isolate-chitosan (SPI-CS) complex. The relationship between surface hydrophobicity, emulsifying activity and emulsion stability and oil-water interfacial tension, particle size and stability of the emulsion were investigated. The results showed that surface hydrophobicity, emulsifying activity, emulsion stability and interfacial adsorption of SPI-CS without ultrasonic treatment were relatively low, and the particle size of the formed O/W emulsion was about 100 μm. The zeta potential of the emulsion was low and the droplets tended to aggregate. Creaming index was the highest after storage for 7 days. Ultrasonic treatment of SPI-CS formed emulsions with markedly improved properties. The O/W emulsion became more stable with increasing ultrasonic power, and it had the highest stability and lowest creaming index at 400 W. However, when the ultrasonic power exceeded 400 W, the particle size of emulsions was increased under light microscope, and zeta potential, emulsifying activity, emulsion stability and interfacial tension decreased obviously. Ultrasonic treatment exposed the internal structure of SPI protein molecules, unfolded part of the protein structure and increased molecular flexibility, thereby promoting the electrostatic interaction between chitosan and the protein, which indicated that ultrasonic-treated SPI-CS could affect the stability and relevant properties of O/W emulsion.

Key words: ultrasonic treatment, soybean protein isolate, chitosan, O/W emulsion, stability