Curcumin encapsulation enhanced by soy protein isolate modified through deamidation and pH-shifting: Mechanistic insights using a novel protein-glutaminase

This study elucidates the mechanism of curcumin encapsulation in soy protein isolate (SPI) modified via enzymatic deamidation and pH-shifting. A novel Chryseobacterium sediminis -derived glutaminase (CS-PG) demonstrated superior thermal stability, catalytic efficiency, and specificity over commercial CP-PG. Controlled deamidation by both enzymes enhanced SPI functionality (solubility/emulsification/foaming) with minimal hydrolysis, where CS-PG induced hydrophobic self-assembly and CP-PG promoted hydrophilic domain formation. These distinct conformations dictated binding modes: CS-PG-SPI achieved 92.97 % higher encapsulation efficiency versus SPI through hydrophobic encapsulation, while attained an 85.00 % increase via surface-layer stabilization. pH-shifting further altered SPI conformation by inducing reversible unfolding and refolding, enabling formation of amorphous, stable protein–curcumin complexes. Dual modification significantly enhanced bioaccessibility versus free curcumin—1034 % for CS-SPI–Cur–pH and 1058 % for CP-SPI–Cur–pH. The work establishes enzymatic deamidation as a precision tool for tailoring SPI self-assembly and bioactive delivery in functional foods.