Enhanced and Green Extraction of Saponins from Gleditsia sinensis Lam. Pods by Ultrasound-Assisted Deep Eutectic Solvents: Optimization and Comprehensive Characterization

Traditional maceration extraction methods for saponins typically involve substantial consumption of organic solvents and long extraction times. To establish an efficient and eco-friendly extraction method for the saponins in Gleditsia sinensis Lam. pods (GSP), deep eutectic solvents (DESs), serving as a sustainable alternative to traditional solvents, have been investigated in conjunction with ultrasound-assisted extraction (UAE) technology. The DES composed with choline chloride and lactic acid in a 1:2 molar ratio was selected based on the highest extraction yield of Gleditsia sinensis Lam. saponins (GSS). The extraction parameters were further optimized using a single factor and response surface methodology (RSM). The maximum GSS extraction yield (183.61 mg/g) was achieved using water content 32%, liquid–solid ratio 35 mL/g, ultrasonic power 427 W, and extraction time 12 min. The structural features of GSS were investigated using ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry, and a total of 16 saponins were tentatively identified. The physicochemical and surface properties of GSS were also investigated. It turns out that GSS solution belongs to pseudoplastic fluid, and the viscosity of GSS solution varied at different pH values. Surface activity analysis showed GSS had a low critical micelle concentration at 0.0161 g/L, and GSS could reduce surface tension to 43.7 mN/m. The foaming and emulsifying evaluations revealed that GSS were an efficient natural surfactant as it could form stable foams and emulsions at low concentrations as compared with Tween 80. Moreover, the antioxidant activities of GSS were studied using antioxidant assay kits, and GSS showed strong capacities in scavenging free radicals. This study reveals the screened DESs coupled with UAE could efficiently separate saponins from GSP, and GSS showed the potential to be applied as natural surfactant or antioxidant in food industry.