Hydrogel formed in situ through Schiff base reaction between gallic acid-grafted soybean protein isolate and oxidized dextran: Interactions, physicochemical properties, and digestive characteristics

Herein, we developed multifunctional hydrogels formed between soybean protein (SPI)-gallic acid conjugate and oxidized dextran (ODex) via a Schiff base reaction. The effects of ODex on the morphology, structure, and functional properties of the hydrogels were elucidated. The results showed that the crosslinking modes in the hydrogels include hydrogen bonding, Schiff bases, Michael addition, and π-π stacking. The synergistic crosslinking of gallic acid and ODex conferred the hydrogels with an appropriate equilibrium swelling ratio, dense morphology, excellent mechanical properties, high thermal stability, and water-holding properties. When the addition of ODex was 0.8 (w/w), the hydrogel had a higher crosslinking degree (76.31 %), smaller average pore diameter (0.322 μm), and higher zero shear viscosity (748.5 mPa. s). In addition, in vitro digestion tests showed that hydrogel degradation was delayed upon increasing the degree of crosslinking, which improved the hydrogel's capacity to adsorb bile salts and control the release of curcumin. This study provides a theoretical basis for the design of high-quality protein hydrogels and other multifunctional materials suitable for various applications.