Ultrasound-cellulase synergy for the extraction of total flavonoids from Astragali complanati Semen and its antioxidant properties

The present study was conducted to optimize ultrasound-cellulase synergy extraction (UCSE) process of flavonoids from Astragali complanati Semen (ACS) adopting response surface methodology (RSM). The extraction efficiency of different extraction progress by UCSE under the 240 W and 480 W were compared, and the antioxidant activities were evaluated in vitro. The effects of five independent variables (cellulase addition, liquid-solid ratio, extraction time, extraction temperature, and ultrasonic power) on the extraction efficiency were explored, and four major factors (cellulase addition, liquid-solid ratio, extraction temperature and ultrasonic power) showing great influences were chosen to study their interactions by RSM. The relationships between ultrasound power 240 W and 480 W on substrates and cellulase were further explored by scanning electron microscopy and 3,5-dinitrosalicylic acid (DNS) method, respectively. The antioxidant activities on 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) radical (ABTS⁺) were evaluated in vitro. The optimal conditions: cellulase addition 930 U/g, liquid-solid ratio 24 mL/g, extraction time 75 min, extraction temperature 64^°C and ultrasonic power 234 W, under the adjusted conditions, the extraction rate was 1.937 g/100 g ACS. Ultrasound power 240 W assisted extraction with cellulase improved the extraction efficiency of the antioxidant. From scanning electron microscopy, the substrate particles were finer and the pores were larger under the function of 240 W, and the enzyme activity test further determined that 480 W could reduce the effect of the cellulase. The UCSE extract exhibited great antioxidant activity in vitro, the IC₅₀ of DPPH is 11.851 µg/mL, and of ABTS⁺ is 23.426 µg/mL.