Optimization of ultrasonic-assisted deep eutectic solvent extraction, characterization, and bioactivities of polysaccharides from Eucommia ulmoides

For the valorization of Eucommia ulmoides (EU) for the functional food industry, the process of ultrasonic-assisted deep eutectic solvent (DES) extraction of EU polysaccharides (EUP) was optimized by response surface methodology. After response surface analysis and experimental verification, the optimum extraction conditions were as follows: the molar ratio of choline chloride to oxalic acid was 0.9:1, the water content of DES was 40.28%, the ratio of material to liquid was 1:22 g/mL, the time was 90 min, and the power was 320 W. The extraction rate of EUP was 1.71%, which was higher than the extraction rate of 0.75% by ultrasonic water extraction under the same conditions, and the optimization effect was better. After DEAE column gradient elution and Sephadex G-75 gel column chromatography, the elution curve and a refined polysaccharide (EUP-1) were obtained. The IC₅₀ values of EUP-1 against α-glucosidase and α-amylase were 0.091 and 0.011 mg/mL. The IC₅₀ values of EUP-1 on DPPH and ABTS·⁺ scavenging were 0.065 and 0.065 mg/mL. The monosaccharide composition of EUP-1 was analyzed as mannose, rhamnose, glucuronic acid, and galacturonic acid in the following molar ratio: 1.00: 1.28: 1.53: 1.88.