Abstract: Objective: To study the mechanism of ultrasonic emulsification of soy protein isolate (SPI) and to investigate the emulsification efficiency of SPI under different ultrasonic powers. Methods: Different ultrasonic powers of 28, 47, 69, 88 and 109 W were used to treat SPI emulsions. The finite element analysis method was applied to simulate the phenomenon of acoustic streaming in the sound field and obtain the distribution of acoustic flow field under different ultrasonic powers. The distribution characteristics of the ultrasonic cavitation field were analyzed by sonochemiluminescence assay. The particle size, emulsification activity, and emulsion stability of SPI emulsions were measured. Results: The effect of ultrasonic cavitation, the cavitation enhancement of acoustic flow, the dispersion and mixing of acoustic flow were the main mechanisms for the homogeneous stabilization of ultrasonic emulsification. Ultrasonic disruption and homogenization as a result of acoustic cavitation could reduce the particle size of SPI emulsions. The acoustic flow effect caused by an increase in ultrasonic power could increase the action area of ultrasonic cavitation enhancing the cavitation effect. Meanwhile, the impact, gyration and vortex motion of acoustic flow could cause the emulsion to be fully stirred, dispersed and mixed, effectively improving the emulsification activity, emulsion stability and apparent stability. The emulsification efficiency of SPI was highest when the ultrasonic power was 88 W. Conclusion: Increased ultrasonic power can effectively improve the emulsification characteristics of SPI.

Key words: soy protein isolate; ultrasonic emulsification mechanism; finite element method; ultrasonic cavitation; acoustic flow effect; emulsification characteristics