Conformational Changes of Soy Proteins under High-Intensity Ultrasound and High-Speed Shearing Treatments

Inspired by denatured globular protein conformational structures, soy protein isolate (SPI) aqueous solutions under neutral pH without the addition of any chemicals were studied under different mechanical treatments. Compared with the traditional magnetic stirring treatment (MS), high-intensity ultrasonication (US), high-speed mechanical shearing (SH), and their combined treatments (USSH, SHUS) were able to better dissolve SPI and further swell and deform the globular conformation. Higher solubility, lower turbidity, enlarged particle size, much uniform particle size distribution, higher free sulfhydryl groups content, increased fluorescence intensity, higher surface hydrophobicity, and higher viscosity SPI solution properties were detected from all these US and SH treated protein samples. Among them, the USSH treated SPI solution was characterized to have the proteins in the best modified conformational structure. The polymer chain relaxation and degradation were also observed from the denatured protein solutions after up to 12 days of treatments. A schematic structure model focusing on the effect of dissolution and denaturation of SPI was established to better explain the results.