Effects of Ultrasonic Treatment on Gel Rheological Properties and Gel Formation of Soybean Protein Isolate

Soybean protein isolate(SPI),used as the raw material,was treated by ultrasonic waves at different powers(100,200,400,600 and 800 W)to explore the effect of ultrasonic treatment on the gelling properties of SPI,while the small amplitude oscillatory shear mode of TA rheometer was utilized to further analyze the effect on the rheological properties and gel formation of SPI. The results showed that ultrasonic waves could not only reduce the storage modulus(G'),loss modulus(G″)and apparent viscosity but also changed the initial viscoelasticity of the SPI dispersing agent. The results of experiments simulating the thermal gel process of SPI showed that the ultrasonic treatment could change the gelling ability of SPL. Ultrasonic waves weakened the gel formation ability of SPI at low powers,and delayed the gel formation process at high powers. However,the use of medium-power(200~600 W)ultrasonic waves could significantly improve the gel performance and accelerate the gel formation of SPI. The ultrasonic treatment conducted at medium powers remarkably increased the viscoelastic property of the SPI gel,with the best effect obtained from the 400 W ultrasonic group,of which the resulting gel had the maximum G' and G″ as well as the minimum loss tangent(tanδ). Medium-power ultrasonic waves could change the initial viscoelastic structure of the SPI dispersing agent to increase the sites of hydrophobic interactions and hydrogen bonding during the formation of thermal gel,thus forming the gel with a three-dimensional net structure of higher strength and density. Ultimately,it can be concluded that ultrasonic waves at the appropriate power can enhance the gel performance of commercial SPI.