A green ultrasound-assisted enzymatic extraction method for efficient extraction of total polyphenols from Empetrum nigrum and determination of its bioactivities

• Polyphenols of E. nigrum was extracted by ultrasound-assisted enzymatic method. • The extraction was optimized by factorial design and response surface methodology. • The extraction yield was significantly higher than other extraction methods. • The extracts showed strong antioxidant and antibacterial activities. In this study, a green and efficient ultrasound-assisted enzymatic extraction (UAEE) method was established for total polyphenols (TPP) extraction from E. nigrum aerial parts. Fractional Factorial design (FFD) was initially implemented for the selection of significant parameters affecting TPP yield and then Box-Behnken design-response surface methodology (BBD-RSM) was employed to optimize the parameters. The optimum extraction conditions for UAEE were as follows: incubation temperature of 38.39 ℃, incubation time of 3.39 h, tannase of 386.53 U/g of sample (U/g), and cellulase of 224.42 U/g. Under the optimum conditions, the TPP yield was 52.17 ± 0.39 mg/g, which was 1.62 and 1.73 times those of the methods of ultrasound-assisted extraction (UAE) and enzyme-assisted extraction (EAE), respectively. The crude extract was purified by HPD-600 microporous resin, and the purity was improved from 8.11% to 22.56%. In addition, the results of antioxidant and antibacterial activity assays showed that the purified extract has stronger bioactivities in contrast with the crude extract. This study indicated that UAEE was an effective technique for the extraction of TPP from the aerial parts of E. nigrum , and TPP extracted by this extraction method could be applied in pharmaceuticals, cosmetics, and food industries.