Soybean protein isolate/sodium alginate double-network hydrogels with high mechanical strength via synergistic cross-linking of imine and ionic bonds.

Herein, we present a simple and novel method to prepare soybean protein isolate (SPI)-based hydrogels with good mechanical characteristics. First, SPI/DSA hydrogels were prepared using SPI and different M/G ratios (1:2, 1:1, and 2:1) of dialdehyde sodium alginate (DSA). Then, the hydrogels were immersed in CaCl2 solution to form SPI/DSA@Ca double network hydrogels. It was shown that the network structure of SPI/DSA hydrogels was enhanced with increasing proportion of G units in DSA. In addition, Ca2+ immersion significantly improved the mechanical properties of the hydrogels. Under 50 % strain, the compressive strength of SPI/DSA-1:2@Ca was 28 kPa, which was 4.24 times higher than that of SPI/DSA-1:2 hydrogel. Overall, this study reveals the effect and acting mechanism of DSA and Ca2+ on SPI-based hydrogels.