Ultrasonic-assisted extraction of zeaxanthin from Lycium barbarum L. with composite solvent containing ionic liquid: Experimental and theoretical research

• The effects of composite solvents containing different ionic liquids on the extraction yield of zeaxanthin were studied. • Extraction and saponification of zeaxanthin could be conducted simultaneously by using composite solvent. • The extraction mechanism of ionic liquids was studied by quantum chemical calculation. • Extraction conditions were optimized by single factor and response surface methodology. Zeaxanthin is the main active ingredient of Lycium barbarum L. The current extraction methods of zeaxanthin are not only tedious and time-consuming but also environmentally unfriendly. Therefore, in the present study, an efficient simultaneous extraction and saponification method for extracting zeaxanthin from L. barbarum was established by using the composite solvent composed of ionic liquid (IL), ethanol, and inorganic base with the assistance of ultrasonic waves. The yield of zeaxanthin was evaluated by high-performance liquid chromatography (HPLC). The optimal ionic liquid, [Hmim][OAc], was selected by combining experimental research with quantum chemical calculation. The extraction mechanism was investigated by quantum chemical calculations combined with density functional theory (DFT), atoms in molecules (AIM) and reduced density gradient (RDG) analyses, and the hydrogen bonds and van der Waals interactions between zeaxanthin and ILs were the main driving forces for ionic liquid extraction. The extraction conditions were optimized using single-factor and response surface methodology as follows: KOH concentration of 6.3%, ionic liquids concentration of 0.09 g/mL, ultrasonic treatment time of 39 min, solid-liquid ratio of 1:40, and the ultrasonic power of 420 W. Compared with the traditional extraction method, the newly established method improved the extraction yield by 23.08% and shortened the extracting time by 90%. Meanwhile, high purity of zeaxanthin could be easily recovered from the ILs solution.