Abstract: This research was conceived to optimize the ultrasonic-assisted enzymatic extraction of flavonoids from mung bean coat by using a Box-Behnken design with response surface methodology (RSM). A quadratic regression model was established using Design-Expert software version 8.0.5.0 based on a Box-Behnken statistical design to describe the yield of flavonoids as a function of ultrasonic power, ultrasonication time, enzyme dosage and hydrolysis time. The optimal extraction conditions were determined as follows: ultrasonic power, 192 W; ultrasonication time, 28 min; enzyme dosage, 0.24%; and hydrolysis time, 40 min. Under these conditions, the yield of flavonoids was experimentally measured to be (0.831 ± 0.02)% (n = 3). Good agreement was observed between the experimental and model predicted values, indicating good fitness. Compared with conventional ultrasonic extraction, the yield of flavonoids was improved by 18.54% using the combined procedure. Spectroscopic analysis showed the characteristic peaks of flavonoids, confirming the presence of these compounds in mung bean coat extracts. By ultra high performance liquid chromatography (HPLC) analysis, the coat of germinating mung beans mainly contained vitexin (51.99%) and isovitexin (45.42%).

Key words: response surface methodology, mung bean coat, flavonoids, ultrasonic method, enzymic method, identification