Study on extraction and antioxidant activity of polysaccharides from Radix Bupleuri by natural deep eutectic solvents combined with ultrasound-assisted enzymolysis

A green and efficient extraction method for Radix Bupleuri polysaccharide (RBP) by natural deep eutectic solvents (NADES) combined with the ultrasonic-assisted enzymolytic extraction (UAEE) was established. Using UAEE, the NADES with different ion combinations were selected to extract RBP. The best technical conditions of NADES combined with UAEE were determined by a single factor experiment and response surface optimization experiment. The results showed that the best extraction process of RBP with NADES was as follows: the molar ratio of urea to choline chloride was 1:3, the water content was 20%, the ratio of material to liquid was 1:30, the ultrasonic power was 400 W, the temperature was 57.34 °C, pH was 4.89, and the amount of enzyme was 2.63%. The extraction rate of RBP was 10.1042%, and the relative error compared with the predicted value was 2.03%. The reuse of NADES not only has little effect on the extraction rate of RBP but also has the highest extraction rate when it is reused for the third time, indicating that NADES has certain recyclability. The in vitro antioxidant activity of polysaccharides extracted from Radix Bupleuri by NADES showed that the extract had a specific ability to DPPH, ABTS, and hydroxyl radicals. Therefore, this study proposed a new, green, and recyclable extraction method for extracting RBP from Radix Bupleuri, which provided a theoretical basis for the in-depth understanding of the physical and chemical properties of RBP and the development and utilization of its biological activities.