Enhanced ultrasound-assisted enzymatic hydrolysis extraction of quinolizidine alkaloids from Sophora alopecuroides L. seeds

Quinolizidine alkaloids are the main bioactive components in Sophora alopecuroides L. This study reports a novel ultrasound-assisted enzymatic hydrolysis method for the extraction of these important alkaloids. Box–Behnken design, a widely used response surface methodology, was used to investigate the effects of process variables on ultrasound bath-assisted enzymatic hydrolysis (UAEH) extraction. Four independent variables, pH, extraction temperature (°C), extraction time (min) and solvent-to-material ratio (mL/g), were studied. For the extraction of sophocarpine, oxysophocarpine, oxymatrine, matrine, sophoramine, sophoridine and cytisine, the optimal UAEH condition was found to be a pH of 5, extraction temperature of 54 °C, extraction time of 60 min and solvent-to-material ratio of 112 mL/g. The experimental values obtained under optimal conditions were fairly consistent with the predicted values. UAEH extraction was then compared with reflux heating, enzymatic extraction and ultrasound-assisted extraction. Of these extraction methods, UAEH extraction under optimal conditions produced the highest yield for seven types of alkaloids. In addition, UAEH extraction resulted in lower ingredient degradation than reflux heating extraction.