pH and ultrasound driven structure-function relationships of soy protein hydrolysate

The structural, thermodynamic and functional properties of soy protein hydrolysate (SPH) modified by treatment at different pH values (3, 5, and 9 and pH 7 as control) followed by ultrasound treatment (240 W, 30 min) were investigated. The treatment of SPH at alkaline pH combined with ultrasound treatment resulted in a reduction in the particle size and turbidity, enhancement in the surface negative charge and disulfide bond (SS) content, and exposure of more surface sulfhydryl (SH) groups, resulting in increased surface hydrophobicity and fluorescence intensity compared to those of the samples treated at pH 3–7. In addition, the alkaline-treated samples were more structurally stable than those treated at other pH values, having higher denaturation temperatures and enthalpies; moreover, these samples had higher solubility and emulsifying and foaming capacities. In addition, ultrasound-assisted pH treatment altered the secondary and tertiary structures of SPH by altering the covalent and non-covalent interactions, although there was no effect on the molecular weight distribution of proteins. In conclusion, ultrasound-assisted pH treatment is an effective method to improve physicochemical properties of SPH for applications in the food industry.