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

Abstract

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.