Mechanism study on the effect of heat shock on the functional characteristics of soybean protein isolate by regulating the change of endogenous enzyme activity in soybeans

The effect mechanism of endogenous enzyme activity on the functional properties of soybean protein isolate (SPI) under heat shock was investigated. Results represented that protease activity of soybeans increased by 114.59% after a 3-min double blanching at 80 °C. Due to endogenous protease enzymolysis changing the protein structure and exposing hydrophobic groups, SPI treated with double blanching at 80 °C for 3 min had the lowest solubility and a 95.73% drop in water absorption. Meanwhile, the surface hydrophobicity, emulsifying index and oil absorption of SPI increased by 126.54%, 137.98% and 51.25%, respectively, compared to unblanched. As the subsequent soaking process advanced, activity of lipoxygenase dropped, activities of protease and carbohydrate-related enzyme were enhanced, the hydrolysate content was increased during, and the rate of water absorption was accelerated with visible holes appearing in the soybeans. On this basis, the hydrophilic compounds finished the fast hydration process to make the endogenous proteosomes pliable and more amenable to the action of proteases, thus resulting in the loose and disordered structure of the protein and the altered characteristics of SPI. These findings suggested that properties of SPI were affected by the combined action of a variety of endogenous enzymes during soaking. Therefore, the heat shock of soybeans is a promising method for the modification of SPI.