Optimization of Ultrasonic-Assisted Extraction of Flavonoids from Ilex Latifolia Thunb by Response Surface Methodology and their Influence over the Activity of Xanthine Oxidase

We have examined the ultrasonic ethanol extraction of Ilex latifolia Thunb flavonoids and the inhibitory effect of these flavo¬noids on xanthine oxidase. Four single-factor extraction conditions were examined: ethanol concentration (%), solid–liquid ratio (g/mL), ultrasonic extraction temperature (°C), and ultrasonic extraction time (min). With these data, the response surface methodology was adopted to optimize the ultrasonic extraction parameters. The optimal ultrasonic extraction parameters were determined to be the ethanol concentration of 49%, the solid-to-liquid ratio of 1:27, the ultrasonic extraction temperature of 74°C, and the ultrasonic extraction time of 97 min. Under the optimal conditions described ear¬lier, the experimental yield of flavonoids was 6.367% with a relative standard deviation of 1.9%, which was comparable to the theoretical extraction rate. The half maximal inhibitory concentration of flavonoids for xanthine oxidase is 5.50 mg/mL. The inhibitory effect was competitive and reversible, with an inhibitory kinetic constant Ki of 2.35 mg/mL.