Desirability function approach for the optimization of microwave-assisted extraction of saikosaponins from Radix Bupleuri

Microwave-assisted extraction (MAE) was applied to the extraction of saikosaponin a, c and d from Radix Bupleuri. Several operating parameters, namely microwave power, time, temperature and ethanol concentration, were optimized using response surface methodology (RSM) with a central composite rotatable design (CCRD). The ethanol concentration and time were found to be the most significant factors (p < 0.0001) for the extraction of all three saikosaponins. By using the desirability function approach, the optimum MAE conditions to obtain desirable extraction yields for all these saikosaponins simultaneously were found at the microwave power of 360-400 W, ethanol concentration of 47-50%, temperature of 73-74 °C and time of 5.8-6.0 min. At these conditions, the yields from the verification experiments were 96.18-96.91% for saikosaponin a, 95.05-95.71% for saikosaponin c and 97.05-97.25% for saikosaponin d, which were in good agreement with the predicted values.