Enzymolysis and homogenization of soybean protein isolate: Structure and gel properties

The objective of this study was to enhance the gel properties of soybean protein isolate (SPI), which frequently shows heterogeneous qualities and limited functionality in cold-induced Chiba tofu. In the context of practical production conditions, the impact of limited enzymolysis (0.5% hydrolysis) in conjunction with different homogenization pressures (4-14 MPa) on the structural characteristics and gel properties of SPI was determined. The enzymolysis-homogenization combined treatment (E-HCT) showed a significant enhancement in water holding capacity (WHC), hardness, chewiness, springiness and cohesiveness of the gels in comparison to the control group (P < 0.05). At 10 MPa homogenization pressure, the treatment outcome of the papain-homogenization combined treatment (P-HCT) showed better efficacy in comparison to that of the alkaline protease-homogenization combined treatment (AP-HCT): Its WHC reached 90.80% and hardness was 11.26 ± 0.04 Pa, which was 3.08 times higher than the control group. The analysis of intermolecular forces indicated that non-disulfide covalent bonds, hydrophobic interactions, and disulfide bonds were primarily responsible for stabilizing the gel network. Structural characterization using Raman and Fourier transform infrared spectroscopy (FTIR) spectroscopy showed an increase in α-helix and β-sheet content, accompanied by a decrease in β-turn and random-coil. Scanning electron microscopy (SEM) further showed that E-HCT led to a more uniform, smooth, and denser gel microstructure. An evaluation of the strategy showed its efficacy in enhancing the structural integrity and functionality of SPI gels. Of note is the observation that P-HCT at 10 MPa shows potential for application in the domain of high-quality protein-based food products.