Demonstration of feasibility and effectiveness of deep eutectic solvent-water system extraction of RG-I type pectin from wolfberry based on target polysaccharide, solvent and their interactions

Lycium barbarum fruit (wolfberry) is rich in rhamnogalacturonan-I (RG-I) pectin with favorable prebiotic activity. However, there is currently limited research on the targeted extraction of RG-I type pectin from Lycium barbarum fruit (LBP). DES is widely recognized as an efficient solvent for extracting bioactive compounds from plants. In this study, a mixture of choline chloride (ChCl) and propylene glycol (PG) at the molar ratio 1:2 with 20 wt% water content was optimal to extract LBP. The yield and extent of branching of LBP extracted by ChCl-PG-water system (LBP-P) were 1.74-fold and 2.87-fold higher than those of LBP extracted by water (LBP-W), respectively. Compared with LBP-W, LBP-P exhibited higher total neutral sugar and uronic acid contents, as well as lower molecular weight and viscosity. The proliferative ability of LBP-P on six Bifidobacterial strains was 1.06–1.92-fold greater than that of LBP-W. In addition, Fourier transform infrared spectroscopy (FTIR) and apparent viscosity proved that the role of water was to maintain strong hydrogen bonds of DES with reduced viscosity. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and density functional theory (DFT) calculations proved that the role of DES was to penetrate cell walls and interact with target substances. The effective extraction mechanism of the DES-water system was based on cell wall cellulose disassembly, side chain exposure, and high-branched LBP dissolution stages. Our results provided a theoretical basis for targeted extraction of RG-I pectin using new solvents.