Deep eutectic solvent-enzyme complex system for green extraction of essential oil, flavonoids and pectin from citrus peels: Optimization, composition and mechanism

In this work, a deep eutectic solvent (DES)-enzyme complex system was innovatively constructed, combined with microwave hydrodistillation and extraction (DEP-MHE) of essential oil (EO), flavonoids (FLs), and pectin (PE) from citrus peels. A systematic screening was conducted through single-factor and response surface experiments, the optimal conditions were: ChCl/1,2-propanediol of 60% water content, 1.6% cellulase, solid/liquid ratio of 1/12 g/mL, pH of 4, pretreatment of 2 h under 50 °C, microwave irradiation of 20 min under 540 W, resulting in the yields of EO, FLs, and PE of 24.82 ± 0.94 mg/g, 15.87 ± 0.49 mg/g, and 29.34 ± 0.76%, respectively. Compared with reference techniques, the DEP-MHE exhibited higher extraction efficiency, lower energy consumption and less environmental impact, and the EOs contained a higher proportion of oxygenated compounds (45.52%). The extraction mechanism was systematically explored, including viscosity, K-T solvation parameters, pattern substance solubility, enzyme activity, and material characterization. The results showed that the complex system exhibited excellent mass transfer and dissolution properties, which could jointly decompose the cell wall structure by increasing the active sites of cellulase and maintaining high cellulase activity. Moreover, DEP-MHE demonstrated excellent reusability, with the yields remaining above 90% after five cycles. In conclusion, this study presents a novel approach to effectively overcome the physical barrier of plant cell walls, and provides a green and sustainable strategy for extracting active components from medicinal and edible plants.