Optimization of pressure-enhanced solid-liquid extraction of flavonoids from Flos Sophorae and evaluation of their antioxidant activity

The central composite design combined with response surface methodology was used to optimize pressure-enhanced solid-liquid extraction (PSE) of flavonoids from Flos Sophorae. The optimal extraction conditions for PSE were: pressure 460 MPa, ethanol concentration 75%, liquid to solid ratio 32 mL/g, temperature 25 °C, and time 5 min. Under these conditions, the experimental flavonoids yield was 200 ± 8.63 mg/g, which closely agreed with the predicted value (202.915 mg/g). Scanning electron micrographs illustrated the severely structural disruptions of sample cells by PSE. In addition, the PSE extract exhibited a considerable antioxidant activity in a dose-dependent manner. Four flavonoids compounds including rutin, kaempferol, quercetin, and genistein were identified and quantified by HPLC analysis of PSE extracts, which contents of dry extract were 368.71 ± 5.46, 104.17 ± 6.25, 89.23 ± 4.84 and 32.31 ± 3.42 mg/g, respectively. These results indicated that PSE was a suitable approach for the extraction of flavonoids from Flos Sophorae.