Enzyme-assisted Ultrasonic Extraction of Total Flavonoids from Brassica rapa L.Optimization and Its Antioxidant Activity Analysis

In this study, the extraction of total flavonoids in Tibetan turnip by enzyme-assisted ultrasonic technology and its antioxidant activity were studied. We used the yield as an indicator, and the Plackett-Burman experiment was conducted to screen out the three factors that had the most significant effect on yield: Compound enzyme ratio, material-liquid ratio and ultrasonic power. The extraction of total flavonoids in turnip was then optimized by response surface methodology. While the antioxidant activities of total flavonoids were evaluated by DPPH and ABTS⁺ free radical scavenging experiments. The results showed that the optimal conditions for the extraction of total flavonoids from turnip are: The compound enzyme ratio was 1.9:1 g/g, the compound enzyme dosage was 2%, the material-liquid ratio was 1:38 g/mL, the ethanol concentration was 75%, the enzymolysis temperature was 50℃, the enzymolysis time was 55 min, the ultrasonic power was 204 W, and the ultrasonic time was 60 min. Under these conditions, the maximum yield of total flavonoid was 1.458%. The results of anti-oxidation experiment showed that the IC₅₀ of DPPH free radical scavenging was 185.6 μg/mL, and was 164.3 μg/mL of ABTS⁺ free radical scavenging, which indicated the total flavonoids of turnip had antioxidant activity in vitro. In summary, this study showed the conditions for the extraction of total flavonoids in turnips by enzyme-assisted ultrasonic method, and the total flavonoids had strong antioxidant activity, which would provide scientific basis for the future development and utilization of Tibetan turnips.