The effect of high intensity ultrasonic pre-treatment on the properties of soybean protein isolate gel induced by calcium sulfate

High-intensity ultrasound (HUS; 20 kHz at 400 W for 5, 20 or 40 min) pre-treatments of soy protein isolate (SPI) changed the particle distribution and reduced particle size of SPI dispersions. Surface hydrophobicity and free sulfhydryl (SH) content of SPI increased with HUS time. Free SH content of CaSO4-induced SPI gels (CISGs) and protein solubility in the presence of SDS and urea decreased after HUS pretreatments, suggesting HUS facilitated disulfide bond formation during CISG formation. HUS resulted in more uniform and denser gel network, water holding capacity (WHC) and gel strength of CISG. Furthermore, WHC and gel strength were positively correlated with free SH content of heated SPI and surface hydrophobicity of unheated SPI, and negatively correlated with particle size of heated SPI and free SH content of CISG. In conclusion, HUS induced structural changes in SPI molecules, leading to different microstructure and improved WHC and gel strength of CISG.