Phenolic extracts from Rhus verniciflua Stokes bark by decompressing inner ebullition and their antioxidant activities

Decompressing inner ebullition (DIE) can reduce the extraction liquid boiling point and polyphenols oxidation in the extraction process. The aim of this study is to optimise the phenolic extraction process by DIE and to examine the antioxidant activities. The extraction process parameters were observed by central composite design. The antioxidant activity was measured using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing power assays. The results showed that the optimal extraction condition is extract time of 90 min, temperature of 45°C, solid–liquid ratio of 1:20 g/mL, vacuum degree of − 0.08 MPa, ethanol concentration of 60%, while the phenolic content was 5.4%. The phenolic extracts from Rhus verniciflua Stokes bark had better antioxidant activities; the antioxidant activity (IC50) of the DIE was 20 μg/mL by the DPPH method. The reducing power of the phenolic extracts was significantly related to their total phenolic content (R = 0.9903). The results presented show that the DIE method is an effective method for polyphenols extraction.