Abstract: Objective: To explore the optimal ultrasonic-assisted extraction conditions of total flavonoids from Mentha haplocalyx Briq. leaves and evaluate the antioxidant activity. Methods: Based on the single-factor tests, the ultrasonic extraction conditions of total flavonoids from Mentha haplocalyx Briq. leaves were optimized by response surface methodology in order to increase the extraction rate of total flavonoids. Meanwhile, the antioxidant activity of total flavonoids was assessed by scavenging assays of hydroxyl and superoxide anion free radicals. Results: The optimal extraction conditions of total flavonoids were ethanol concentration of 80%, material-liquid ratio of 1:40, extraction time of 118 min and extraction temperature of 62 ℃. Under the optimal conditions, the maximum extraction rate of total flavonoids was 6.11%. Extracted total flavonoids had strong scavenging capacity on hydroxyl and superoxide anion free radicals in a dose-dependent manner. Conclusion: Response surface methodology is applicable for the optimization of ultrasonic extraction of total flavonoids from Mentha haplocalyx Briq. leaves. The total flavonoids from Mentha haplocalyx Briq. leaves have strong antioxidant capacity. These investigations will be theoretical reference for further development and utilization of Mentha haplocalyx Briq..

Key words: Mentha haplocalyx Briq., flavonoids, ultrasonic extraction, response surface methodology, antioxidant activity