Modification of soybean protein isolate by pH-shifting combined with ultrasonic treatment: Structural, viscosity, and functional properties

In order to reduce the viscosity of soybean protein isolate (SPI) and improve its processing suitability, this study investigated the impact of pH-shifting and ultrasonic treatments on the structure, viscosity and functional properties of SPI. The results indicated that both without and with ultrasonication, the pH-shifting, especially the treatment of alkaline pH-shifting decreased alpha-helix and beta- sheet contents and particle size of SPI, while increased its beta- turn and random coil contents, fluorescence intensity, surface hydrophobicity and free sulfhydryl content. The alkaline pH-shifting combined with ultrasonic treatments reduced the viscosity of SPI from 98.97 mPa.s to 22.83 mPa.s. These structural changes endowed SPI with higher solubility (from 81.13 % to 91.53 %), and better emulsifying and foaming properties. Moreover, principal component analysis (PCA) was employed to visualise the influences of pH-shifting and ultrasonic treatments on SPI, confirmed that the structural changes of SPI were correlated with its viscosity and functional properties. These results have important implications for promoting the application of SPI in fluid food.