Improving the physicochemical properties of composite yuba with whey protein isolate by ultrasound treatment: study on the film-forming ability and structure

Abstract Yuba is a traditional soy product made from soymilk. However, producing nutritious yuba with high quality and yield remains a challenge. This study aimed to optimise the mechanical and nutritional properties of yuba by adding whey protein isolate (WPI). The impact of ultrasound powers (0–800 W) on the physicochemical properties of WPI–soymilk dispersions and their product-yuba was studied. The composite soymilk at 400 W had the highest surface hydrophobicity (3917.25 ± 10.54) and free sulphydryl content (52.31 ± 0.39 μmol/g protein). Compared with the control, ultrasound reduced the particle size of the soymilk and shifted the distribution from multimodal to unimodal. Meanwhile, the composite soymilk exhibited shear thinning behaviour and the apparent viscosity of ultrasound-treated group was lower than the untreated group. Compared with the non-ultrasound samples, the tensile strength of composite yuba significantly increased by 8%, while the elongation at break decreased by 22% at 200 W. The formation of composite yuba was mainly facilitated by the hydrogen and disulphide bonds between WPI and soymilk under ultrasound treatment, which was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. These findings provided some vital evidence for the utilisation of ultrasound in the processing of yuba with addition of WPI.