Conformational evolution of protein fractions in chitosan-whey protein isolate coacervates as influenced by molecular weight of ligands for modulating pickering particle features.

Self-assembled complexes of chitosan (CS) and whey protein isolate (WPI) with varying molecular weights were prepared under ultrasound-driven conditions to explore their potential as Pickering particles for stabilizing emulsions. This study investigated how side-chain molecular characteristics and ligand-induced conformational changes of proteins influenced functional properties of the self-assembled protein-polysaccharide complexes. As the molecular weight of CS decreased within the supramolecular complex system, a greater degree of WPI unfolding was induced, leading to the formation of a more compact WPI-CS complex. The accompanied sheltering effects of aromatic amino acids within the CS-induced unfolding structure of WPI promoted stronger interactions between WPI and CS, driven by electrostatic interactions, hydrogen bonding, and hydrophobic forces. The increased binding affinity resulted from a more flexible and loosely stacked WPI protein structure which transitioned from an ordered to a more disordered conformation after complexation. Particularly, the incorporation of low-molecular-weight CS induced substantial WPI conformational changes, exposing hydrophobic groups, amphiphilic functional groups, and disulfide bonds, thus contributing to increased emulsion stability, foaming ability, and foam stability of the emulsions using WPI-CS as complex Pickering particles. These findings highlighted the feasibility of modification of sugar ligands-mediated protein unfolding features in modulating the physicochemical properties of the protein-based complexes.