Ultrasonic-assisted enzymatic extraction of phenolics from broccoli (Brassica oleracea L. var. italica) inflorescences and evaluation of antioxidant activity in vitro

摘要

An efficient ultrasonic-assisted enzymatic extraction technique was applied to extracting phenolics from broccoli inflorescences without organic solvents. The synergistic model of enzymolysis and ultrasonication simultaneously was selected, and the enzyme combination was optimized by orthogonal test: cellulase 7.5mg/g FW (fresh weight), pectinase l0mg/g FW, and papain 1.0mg/g FW. The operating parameters in ultrasonic-assisted enzymatic extraction were optimized with response surface methodology using Box-Behnken design. The optimal extraction conditions were as follows: ultrasonic power, 440 W; liquid to material ratio, 7.0:1 mLVg: pH value of 6.0 at 54.5 °C for 10min. Under these conditions, the extraction yield of phenolics achieved 1.816 ±0.0187 mg gallic acid equivalents/gram FW. The free radical scavenging activity of ultrasonic-assisted enzymatic extraction extracts was determined by 1,1-diphenyl-2-picrylhydrazyl assay with EC_(50) values of 0.25, and total antioxidant activity was determined by ferric reducing antioxidant power assay with ferric reducing antioxidant power value of 0.998 mmol FeSOVg compared with the referential ascorbic acid of 1.184 mmol FeSO_4/g.