The strengthening effects of different types of salt on the mechanical properties of soy protein isolate and pea protein isolate composite gels

Plant-based proteins are of high demand due to their nutritional value and unique functionality. However, the soft and fragile characteristics of plant-based thermal gels limit their applications. To improve the mechanical properties of heat-induced legume protein gels, this study introduced four types of salt (NaCl, KCl, MgCl2 and CaCl2) into SPI/PPI composite gels and investigated the strengthening effects of different concentrations of salt on the composite gels. When the concentration of Na+ and K+ was between 50 and 150 mmol/L, and that of Mg2+ and Ca2+ was between 5 and 15 mmol/L, the whiteness and hardness of SPI/PPI composite gels increased, while the storage modulus and loss modulus also increased. In addition, the introduction of salt induced interconversion of the secondary structures within SPI/PPI, leading to a considerable augmentation of the more structurally stable beta-sheets. Scanning electron microscopy analyses further revealed that appropriate concentrations of salt induced the formation of a dense and stable network structure in the SPI/PPI composite gels. This work provides a route to produce plant-based protein gels with enhanced mechanical properties, and it also benefits developing other plant-based products.