Differential Enzymatic Hydrolysis: A Study on Its Impact on Soy Protein Structure, Function, and Soy Milk Powder Properties

Protein constitutes the primary nutrient in soy, and its modifications are intricately linked to the properties of the soy milk powder. This study employed six main commercial enzymes (bromelain, neutrase, papain, trypsin, flavourzyme, and alcalase) to investigate the impact of enzymatic hydrolysis on the structural and functional properties of soy protein isolate (SPI), as well as its influence on the physicochemical properties of soy milk powder. The findings indicated that each of enzymes exhibits distinct specificity, with the degree of hydrolysis following the order: alcalase > flavourzyme > papain > bromelain > neutrase > trypsin. Enzymatic hydrolysis facilitates the unfolding of SPI, leading to the exposure of chromogenic fluorophores and hydrophobic amino acid residues, which in turn promotes an increase in free sulfhydryl content. Concurrently, this process induces the transformation of α-helix and β-sheet into β-turn and random coil. The enzyme modification enhances the solubility, emulsification, and foaming activities of SPI and significantly augment its antioxidant properties (p < 0.05). However, this enzymatic treatment adversely affects the stability of its emulsification and foaming properties. Subsequent to enzymatic hydrolysis, soy milk powder demonstrated a reduction in particle size and an improvement in solubility, which significantly enhanced its flavor profile. In summary, alcalase offers substantial advantages in augmenting the functional properties of SPI and increasing the solubility of soy milk powder. However, this process adversely affects the flavor profile of soy milk powder, a consequence attributed to the broad hydrolysis specificity of alcalase.