β-Cyclodextrin as a booster for ultrasound-assisted extraction of secoiridoids from Gentiana rigescens using a biobased deep eutectic solvent

In this study, secoiridoids (gentiopicroside, loganic acid, swertiamaroside, and sweroside) were extracted from Gentiana rigescens roots and rhizomes with β-cyclodextrin (β-CD) as the booster and biobased glycine-glycerol deep eutectic solvent (DES) as the extraction solvent and with ultrasound-assisted extraction. The molecular docking performances showed that in DES aqueous solution, β-CD interacts with secoiridoids through noncovalent bonds and hydrogen bonds, and the four secoiridoids studied can be well adapted to the hydrophobic cavity of β-CD. The hydrogen bonds present between secoiridoids and β-CD all reached more than four, and the corresponding binding energies were all lower than − 5.0 kcal/mol. The yields of gentiopicroside, loganic acid, swertiamaroside, and sweroside were 39.82 ± 2.05 mg/g, 6.61 ± 0.34 mg/g, 0.79 ± 0.04 mg/g, and 0.57 ± 0.04 mg/g, respectively, under optimal extraction conditions. The results showed that ultrasound-assisted extraction of secoiridoid compounds in G. rigescens with an aqueous β-CD/DES solution was more effective compared with conventional extraction solvents, which provides a scientific basis for the promising use of β-CD/DES as extraction solvents in natural drugs.