Effects of Selective Enzymatic Hydrolysis on Structural Properties and Gel Properties of Soybean Protein Isolate

Soybean protein isolate (SPI) gel has been demonstrated to exhibit suboptimal stability and a coarse texture. Selective enzymatic hydrolysis modification has been demonstrated to effectively enhance the functional properties and structural stability of the protein. The objective of this study was to modify SPI using alkaline protease and papain. The impact of selective enzymatic hydrolysis on SPI was examined through the analysis of hydrolysis degree (DH), particle size, and protein purity. A systematic exploration was conducted in order to investigate the structural and quality characteristics of SPI gel. Indicators such as secondary structure changes, texture characteristics, water-holding capacity (WHC), rheology, and microstructure were analyzed. The findings indicate that when the DH of the SPI solution is 1%, its particle size is reduced relative to that when DH is 0.5%. The SDS-PAGE results indicated that alkaline protease could hydrolyze most of the 7S and 11S components in SPI into shorter peptides, while papain retained more of the 7S and 11S components and generated peptides with larger molecular weights. Fourier-transform infrared (FT-IR) spectral analysis indicated that following the process of enzymatic modification, the contents of α-helix and β-sheet in the secondary structure of SPI increased, while the contents of β-turns and random coils decreased. In the context of gel performance, it has been demonstrated that papain-modified SPI, attributable to its elevated content of macromolecular peptides, manifests superior WHC, hardness, springiness, cohesiveness, chewiness, storage modulus (G), and microstructure in comparison to alkaline protease-modified gel. Concurrently, the gel performance of papain modified SPI is significantly superior to that of unmodified SPI gel. This research provides a significant theoretical foundation and practical reference for promoting the efficient application of SPI in the domain of food processing.