Optimization of Extraction Technology and Antioxidant Activity of Flavonoids from Walnut Kernel Pellicle

In order to optimize the ultrasonic extraction technology of flavonoids from walnut kernel pellicle and its antioxidant activity and main components,the response surface methodology(RSM)was used to study the effects of ethanol concentration,liquid-material ratio and extraction temperature on the yield of flavonoids based on the single experiment. The antioxidant capacity of the extract was determined by salicylic acid colorimetry and pyrogallol autoxidation,and the main chemical composition were identified by UPLC-MS/MS.The results showed that when the concentration of ethanol was 59%,the liquid-material ratio was 1:52 g/mL,the extraction temperature was 41 ℃,the ultrasonic power was 500 W,and the extraction time was 30 min,the yield of flavonoids in kernel pellicle was 15.58%. The antioxidant activity test showed that in the concentration range of 10~50 μg/mL,the maximum scavenging rates of ·OH and ·O₂^- by endotestal flavonoids were 73.25% and 65.27%,respectively. A total of 119 flavonoid compound were identified by UPLC-MS/MS platform analysis,including 52 flavonols,18 flavonols,18 flavanoids,8 dihydroflavonoids,5 anthocyanins,5 isoflavones,3 dihydroflavonols and 2 chalcone. Therefore,the optimized ultrasonic extraction of walnut kernel pellicle flavonoids has a good effect with a strong antioxidant effect and identified its main components,which lays a foundation for the development and utilization of walnut resources.