Ultrasonic–Microwave-Assisted Extraction of Flavonoids from Citri Reticulatae Pericarpium and Antioxidant Evaluation of Three Purified Flavonoid Compounds

The aim of this study was to optimize ultrasonic–microwave cooperative extraction (UMCE) conditions for flavonoids from Citri Reticulatae Pericarpium (CRP) and to evaluate the antioxidant activities of the purified flavonoid compounds. Using a Box–Behnken design for the experimental study, the influence of each variable on yield was determined, and the optimal conditions for the extraction of these compounds were discovered. The optimal parameters for maximum yield were determined to be 160 W ultrasonic power, 630 W microwave power, 68 °C temperature, 40 min, 57% ethanol and 1:20 ratio of solid to liquid. The primary flavonoids present were hesperidin (13.99 mg/g), nobiletin (4.02 mg/g) and tangeretin (3.80 mg/g). The antioxidant test results showed that hesperidin had greater antioxidant activity than both nobiletin and tangeretin. Based on the results of this study, ultrasonic–microwave cooperative extraction was shown to be an effective approach for enhancing flavonoid recovery from CRP. These findings provide useful insights into the extraction and antioxidant properties of CRP flavonoids and may contribute to the future development of value-added applications of CRP resources.