Abstract: Total flavonoids were extracted from geminated brown rice by ultrasound-assisted extraction method using 50% ethanol as extraction solvent. Response surface methodology was employed to optimize the extraction conditions based on extraction rate. A quadratic regression model describing the effects of four process conditions on the extraction rate of total flavonoids was developed using a Box-Behnken experimental design. The response surface analysis showed that the optimal extraction conditions were extraction for 30.5 min at 45.8 ℃ and a material/liquid ratio of 18.9:1 (mL/g) after 11.7 min of ultrasound treatment. Under these conditions, the average extraction rate of total flavonoids was (0.743 ± 0.011) mg/g (n = 5), accounting for 98.5% of the predicted value, 0.754 mg/g. The developed regression model showed excellent goodness of fit.

Key words: germinated brown rice, flavonoids, ultrasound, response surface methodology (RSM)