Mechanism of change of the physicochemical characteristics, gelation process, water state, and microstructure of okara tofu analogues induced by high-intensity ultrasound treatment

Abstract The effects of high-intensity ultrasound treatment on the physicochemical characteristics, gelation process, water state, and microstructure of okara tofu analogues were evaluated. Suspensions composed of okara and SPI were treated with ultrasound at different power settings (0, 500, 600, 700, or 800 W) for 20 min, and then, the physicochemical characteristics of the suspensions and okara tofu analogues gelation were determined. After ultrasound treatment at different power settings, the mean particle size of the suspension samples decreased, whereas the surface hydrophobicity and free sulfhydryl group contents of the suspension samples increased. The suspension samples exhibited different gelation behaviors, resulting in distinct water-holding capacities, textural properties, and microstructures in the final treated okara tofu analogues. With increasing ultrasound power from 500 W to 800 W, the water-holding capacity and gel yield of the okara tofu analogues first increased and then decreased. When the ultrasound power was set to 600 W, maximum values of the water-holding capacity and gel yield of 73.95% and 97.48%, respectively, were reached. The textural properties were as follows: hardness, 656.75 g; springiness, 1.203 mm; cohesiveness, 0.435 g mm; gumminess 285.75 g; and chewiness, 343.76. The overall acceptability score increased to the highest. Compared with that of the control sample, the T21 relaxation time of okara tofu analogues decreased to 45.43 ms and its peak area increased to 94.97%; the okara tofu analogues showed a more uniform and denser gel network with filamentous and homogeneous pores; and the okara fibers were embedded more uniformly in the network. Therefore, high-intensity ultrasound changed the microstructure and physicochemical properties of okara fibers and proteins, producing a firm and uniform okara tofu analogues gel network. This study can provide a thorough understanding of the gelling properties of okara tofu analogues.