Gallic acid-functionalized soy protein-based multiple cross-linked hydrogel: Mechanism analysis, physicochemical properties, and digestive characteristics

[Display omitted] •The protein-phenolic compound conjugates formed via CN bonds.•The structures and antioxidant properties of these conjugates were investigated.•Multiple protein-polyphenol cross-linked hydrogels were synthesized.•Hydrogels contain hydrogen bonds, Michael additions, and Schiff base crosslinks.•The SPI-GA hydrogels effectively inhibited the degradation of the protease. Herein, carbodiimide hydrochloride/N-hydroxysuccinimide was used to mediate the grafting of gallic acid (GA) (0.005, 0.0015, and 0.025 wt%) with soybean protein isolate (SPI) in the preparation of SPI-GA conjugates and hydrogels. The modified materials were primarily joined via the CN bonds and exhibited excellent antioxidant properties. In addition, spectral analysis revealed that the grafting of GA increased the flexibility of the SPI structure. The SPI-GA hydrogel is fabricated through covalent/non-covalent cross-linking mechanisms, including Schiff base, Michael addition, and hydrogen bonding. Furthermore, the microstructure, rheological properties, thermal stability, and textural properties of the hydrogel were affected by the amount of GA grafted. The SPI-GA hydrogel exhibited the best performance when the amount of GA graft was 0.015 wt%. Furthermore, the tightly cross-linked structure of SPI-GA prevented premature degradation of the protein by pepsin. In conclusion, these capabilities provide numerous possibilities for the development of multifunctional and active substance delivery carriers.