Optimization of ultrasound assisted acid extraction of pectin from walnut green husk and analysis of its in vitro lipid-lowering and antioxidant activities

[Objective] This study aimed to realize the high value-added resource utilization of walnut production waste. [Methods] Ultrasonic assisted tartaric acid was used to extract pectin from walnut peel. The extraction process was optimized by response surface test, and its lipid-lowering ability and antioxidant activity were analyzed. [Results] Under the control of the conditions of ultrasonic power of 300 W, ultrasonic temperature of 95 ℃, ultrasonic time of 27 minutes, liquid to material ratio of 19∶1 （mL/g）, and pH of 2, the yield of walnut green peel pectin was the highest, reaching 25.92 mg/g. Walnut green peel pectin had good adsorption capacity for cholesterol, binding capacity for bile salts, and inhibitory effect on pancreatic lipase. Walnut green peel pectin also had strong antioxidant effects. When the concentration was 2 mg/mL, the clearance rates of hydroxyl radicals, DPPH radicals, and ABTS radicals reached （78.74±0.58）%, （91.56±1.27）%, and （97.89±0.72）%, respectively. [Conclusion] High-quality walnut green peel pectin could be obtained by optimizing the ultrasonic assisted tartaric acid extraction process. This pectin had good lipid-lowering function and antioxidant activity, and can be used as natural pectin resources for further research and development.