Application of graphene oxide as a catalyst to accelerate extraction of total flavonoids and the hydrolysis of baicalin from Radix scutellaria

A new method, graphene oxide (GO)-assisted ethanol reflux extraction (GERE) was investigated to extract total flavonoids from Radix scutellaria and accelerate the hydrolysis of baicalin (BG) to baicalein (B), simultaneously. The parameters of GERE were optimized by the single factor experiments, the optimal conditions were 1.1 mg GO/g dry raw material, ethanol 60% (v/v), ratio of liquid to solid 15 (mL/g) at 70 °C for 6 h. Under optimized conditions, the yields of total flavonoids and baicalein by GERE reached 24.95% and 0.38%, about 9.72% and 375% higher than single ethanol reflux extraction (ERE), respectively. SEM results revealed that after treated with GO, the Radix scutellaria surface appeared cracks, ravines and small holes. The structural disruption of wall reduces the mass transfer resistance and accelerates the leaching of flavonoids by ethanol solvent. XRD and FTIR results showed that GO reduced the crystallinity and the grain sizes of the Radix scutellaria cell, changed the internal structures of cellulose as well as cellulose accessibility, and improved the hydrolysis efficiency. HPLC results revealed that the content of baicalein in extract by GERE was significantly higher than that by ERE, which means that GO can catalyze the hydrolysis of baicalin to baicalein. The high yields of total flavonoids and baicalein can be related to the catalytic activity of GO, which can lead to the destruction of the cell wall, the reduction of the crystallinity and the grain sizes of cellulose. Thus, it was indicated that GERE method could be an alternative method for natural compounds extraction in industry.