Deep eutectic solvent extraction of polysaccharides from Lycium barbarum residue: Optimization, composition analysis, and antioxidant activity

Lycium barbarum residue (LBR), a by-product of Lycium barbarum processing, is a valuable but underutilized resource. In this study, we develop and optimize an ultrasound-assisted deep eutectic solvent (DES) extraction method to recover Lycium barbarum residue polysaccharides (LBRPs). Among 25 synthesized DESs, ChCl-DES-21 (choline chloride:glycerol:acetamide), had the highest extraction efficiency during the initial screening, with a yield of 6.055 mg/g. This exceeded that of conventional water extraction (4.507 mg/g). A structural characterization Fourier Transform Infrared spectroscopy (FT-IR) and Proton Nuclear Magnetic Resonance ( 1 H-NMR) revealed a robust hydrogen bonding network in ChCl-DES-21. This enhanced the solubility and extraction of Lycium barbarum residue polysaccharides. Extraction conditions were optimized via the Response Surface Methodology (RSM), yielding an extraction rate of 8.486 mg/g under mild conditions of 84% water content, a solid-liquid ratio of 1:46 g/mL, an extraction temperature of 20°C, and an ultrasound time of 20 min. Furthermore, Gas Chromatography–Mass Spectrometry (GC-MS) analysis indicated a higher monosaccharide content in the ChCl-DES-21-extracted LBRPs compared to those extracted with water, specifically glucose (5.86 mg/g versus 4.09 mg/g), D-fructose (3.53 mg/g versus 2.47 mg/g), and D-mannose (0.02 mg/g versus 0.01 mg/g). The antioxidant activities of the extracted polysaccharides were enhanced, and the ChCl-DESs-extracted LBRPs exhibited superior scavenging capacities for DPPH (31.5% at 41.4 μg/mL), ABTS (58.0% at 184 μg/mL), hydroxyl radicals (39.9% at 41.4 μg/mL), and superoxide anions (15.7% at 41.4 μg/mL) compared to those extracted with water. Notably, the antioxidant capacity varied within the same extraction group at different concentrations. In summary, the ultrasound-assisted ChCl-DES-21 extraction method improved the yield and antioxidant activity of LBRPs, providing an efficient and sustainable strategy for the high-value utilization of Lycium barbarum residue. ● ChCl-DES-21 enables efficient extraction of polysaccharides from Lycium barbarum residue. ● Ultrasound-assisted ChCl-DES extraction was optimized for maximum polysaccharide yield. ● Physicochemical properties of ChCl-DES-21 affect polysaccharide extraction efficiency. ● Extracted polysaccharides showed strong antioxidant activity in radical scavenging assays. ● GC-MS revealed glucose and fructose as major monosaccharides in DES extracts.