Abstract: In the present work, the extraction conditions for flavonoids from pubescent holly roots were optimized by response surface methodology (RSM) for achieving maximum extraction rate and DPPH radical scavenging rate of flavonoids. Two polynomial regression models for the extraction rate or DPPH radical scavenging rate of flavonoids as a function of three variables temperature, extraction time and material-to-liquid ratio were established. According to the models, each variable had a significant impact on the extraction rate and DPPH radical scavenging rate of flavonoids from pubescent holly roots. The optimal extraction conditions for simultaneously achieving extraction rate and DPPH radical scavenging rate of flavonoids were extraction time of 90 min, material-to-liquid ratio of 1: 21, and extraction temperature of 79 ℃. Under the optimal extraction conditions, the extraction rate and DPPH radical scavenging rate of flavonoids were 0.419% and 98.8%, which were close to the predicted values. Therefore, RSM optimization can provide a reliable process for extracting flavonoids from pubescent holly roots.

Key words: pubescent holly roots, flavonoids, extraction, response surface methodology, overlapped contour plot