Optimization of an Ultrasound‐Assisted Aqueous Two‐Phase Extraction Technique for Verbascoside From Leaves of Syringa pubescens Turcz. and Activity Evaluation

ABSTRACT

An efficient ultrasound‐assisted aqueous two‐phase extraction method was developed for the extraction of verbascoside from the leaves of Syringa pubescens Turcz. The ethanol/ammonium sulfate system was used as the extraction solvent. Based on the results of single‐factor experiments, the key parameters, including ethanol concentration, ammonium sulfate concentration, and sample mass, were further optimized using response surface methodology. The optimal extraction conditions were obtained as follows: ethanol concentration of 30% (w/w), ammonium sulfate concentration of 19% (w/w), sample mass of 0.63 g, ultrasonic power of 150 W, extraction time of 30 min, and temperature of 40°C. Under these conditions, the experimental verbascoside yield (5.23 ± 0.29 mg/g) was in good agreement with the model‐predicted value (5.33 mg/g), confirming the reliability of the established model. Furthermore, the verbascoside extract exhibited potent radical scavenging activities with half‑maximal inhibitory concentration values of 0.039 mg/mL against α, α‐diphenyl‐β‐picrylhydrazyl and 0.058 mg/mL against 2,2'‐azino‐bis (3‐ethylbenzthiazoline‐6‐sulphonic acid), as well as a ferric‐reducing antioxidant power of 2.78 mg Fe ^{2 +} /g at 2.5 mg/mL. This study demonstrates that the ultrasound‐assisted aqueous two‐phase extraction method is an efficient, green, and reliable approach for the extraction of verbascoside from S. pubescens leaves, and the obtained verbascoside extract shows promise as a natural antioxidant agent for potential applications in the food and pharmaceutical industries.