Complex coacervation of eggshell membrane keratin and gelatin: Interaction mechanism, structural regulation, and functional properties.

Eggshell membrane is an abundant agricultural by-product from the egg-processing industry, most of which is landfilled and thus deprived of high-value valorization. Herein, a mild one-step alkaline procedure was developed to simultaneously extract keratin and gelatin from waste eggshell membrane. Composite protein coacervates were prepared by adjusting pH, sodium chloride concentration and gelatin-to-keratin mass ratio. Their phase behavior, microstructure, molecular interactions and functional properties were characterized to elucidate protein synergistic mechanisms. Quantitative experiments determined the optimal conditions: pH 4.5, 50 mmol/L NaCl, and a gelatin/keratin mass ratio of 8:2. Electrostatic interactions triggered coacervation, while hydrogen bonds, hydrophobic forces and thiol interactions stabilized the network alongside protein conformational transitions and disulfide-bond rearrangement. The optimized 8:2 coacervate showed a compact microstructure, improved rheological and emulsifying performance, and 23.4% free-radical-scavenging activity. This facile green strategy achieves full-value recovery of egg-processing waste and promotes sustainable valorisation of agricultural by-products.