Deep eutectic solvent extraction of Camellia oleifera seed meal protein: Functional properties, antioxidant hydrolysate production and molecular mechanism compared with alkaline extraction.

Conventional alkaline extraction of Camellia oleifera seed meal (COSM) protein is not satisfactory in extraction effects and co-extraction of antinutritional saponins. This study compared five choline chloride-based deep eutectic solvents (DESs). The choline chloride/1,4-butanediol system (DES-5) showed the most favorable balance. In detail, it increased protein content from 33.91% to 50.84% while maintaining a comparable extraction rate (33.12% vs. 30.11%) and reduced saponin-equivalent levels versus alkaline extraction. DES-5-extracted protein (DES5-P) showed higher α-helix content, lower free sulfhydryl content, and significantly improved emulsifying and foaming stability. Density functional theory indicated the DES-5 system is stabilized primarily by hydrogen bonds and supplemented by van der Waals. Molecular dynamics revealed that DES-5 achieved protein extraction mainly through hydrogen bonds and electrostatic interactions. Enzymatic hydrolysates of DES5-P and their <3 kDa fractions showed greater radical-scavenging activity than alkaline-extracted protein. These findings support DES-5 as an effective extraction method for COSM protein valorization.