Efficient ultrasound-assisted enzymatic method for extraction of immunostimulant QS-21 from Quillaja saponaria Molina

QS-21 from the bark of Quillaja saponaria Molina is a triterpene glycoside saponin, a new alternative immunoadjuvant. However, its application is limited because its primary source is the bark of adult trees and current extraction methods result in low yields. Therefore, this work aimed at extracting QS-21 from Q. saponaria Molina using a novel and efficient ultrasound-assisted enzymatic extraction (UAEE) method to improve yields and optimize resource utilization. Based on the single-factor and Plackett-Burman design (PBD) experiments, Central Composite design (CCD) optimum extraction conditions for improving QS-21 yield were established (71.084 min incubation time, 275.887 U enzyme dosage, and 20.254 min extraction time, yielding 5.778 mg/g of QS-21). Additionally, compared with ultrasound-assisted extraction (UAE) and enzyme-assisted extraction (EAE) methods, the UAEE method showed a higher QS-21 yield, which was 1.748 and 1.977 times higher than those of the UAE and EAE methods, respectively. Besides, cytotoxicity and immune activation assays indicated that the extract by the UAEE method exhibited a significant inhibitory effect on the activity of bone-marrow-derived dendritic cells and had a high potential for immune activation, respectively. Overall, the UAEE method can successfully improve the extraction yield of QS-21 from Q. saponaria Molina, representing an efficient and resource-saving method to obtain QS-21 for use as an adjuvant in human vaccines.