PLOS ONETitle - Optimization of the flash extraction of flavonoids from the leaves of Salix babylonica using the response surface method and an evaluation of the leaves high antioxidant activity

Abstract

Many biological activities of Salix babylonica leaves are attributed to the plants high total flavonoid content. Flash extraction has the advantages of high efficiency and maximum retention of the active ingredient. In this study, flash extraction was used to extract the total flavonoids, and a Box-Behnken design was used to optimize the extraction conditions for the first time. The effects of four independent variables, including ethanol concentration, extraction voltage, time, and ratio of liquid to material on flavonoid yield, was determined, and the optimal conditions for flavonoid extraction were evaluated using response surface methodology. Statistical analyses showed that the linear and quadratic terms of these four variables had significant effects. The fitted second-order model revealed that the optimal conditions consisted of an ethanol concentration of 67.91%, extraction time of 87 s, extraction voltage of 116 V and ratio of liquid to material of 42.79. Under the optimum conditions, the experimental value of 66.40{+/-}0.80% nearly coincided with that predicted by the model. In the ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH.) assays, the extracts showed significant antioxidant and scavenging capacity for free radicals, respectively. This study helps to better exploit the resources of Salix babylonica leaves and provides new insights for effective extraction of flavonoids.