Deep eutectic solvent plasticization of chitosan/distiller's grains prolamin films: Hydrogen bond-driven structural regulation and enhanced food preservation performance.

Abstract

Developing sustainable, high-performance hydrocolloid packaging remains challenging because polysaccharide films are typically brittle and provide limited barrier protection. Here, we present a synergistic strategy combining distiller's grains prolamin (DGSP) and deep eutectic solvents (DES) to tailor the structure and performance of chitosan (CS) films. CS/DGSP composites were first optimized for protein incorporation, and subsequently plasticized with three choline chloride-based DES (ChCl-glycerol, ChCl-xylitol, and ChCl-urea) at 0.5-2 wt%. Among the ratios tested, a CS/DGSP mass ratio of 2:1 was selected primarily for its superior barrier performance, with favorable film-forming stability and optical properties. DES plasticization, particularly 0.5 wt% ChCl-urea, further enhanced extensibility, UV shielding, and thermal stability, most notably increasing elongation at break to 70.93%, approximately 14-fold higher than that of the non-plasticized control. Structural characterizations indicated that DES-mediated multipoint hydrogen bonding partially replaced polymer-polymer interactions, enabling dual regulation of chain mobility and network densification. This flexible yet compact network suppressed water permeation while maintaining integrity and homogeneity. Strawberry preservation tests confirmed the superior ability of the optimized film to retard moisture loss, shrinkage, and microbial spoilage without compromising sensory quality. These findings provide a DES-assisted protein-polysaccharide design strategy that enables high-value DGSP utilization and offers mechanistic insights into structure-property relationships for sustainable packaging.