Ultrasonic-assisted Extraction Of Saponins From Xanthoceras Sorbifolium Bunge Leaves And Their Foaming And Emulsifying Properties

Xanthoceras sorbifolium Bunge(X.sorbifolia)is a deciduous shrub of Sapindaceae,which has many applications in medicine,food and ecology.As one of the traditional parts of X.sorbifolia,Xanthoceras sorbifolium Bunge leaves(XLs)have a long history of food and medicinal use,which has the effects of stabilizing capillaries,stopping bleeding and lowering cholesterol,etc.In March2023,XLs have also been incorporated into the new resource food raw materials.The biomass yield of leaves exceeds that of fruits,but most of them are naturally decayed or burned.Their intensive processing and utilization have become an urgent problem to be solved in industrial development,and thus this paper focuses on this topic.Saponins are the most abundant bioactive compounds in XLs,but the extraction and purification of saponins from XLs are still lacking,especially with green,safe and efficient methods;Meanwhile,the processing characteristics of saponins from XLs are not studied systematically.Hence,in this paper,we studied the extraction of saponins from XLs by ultrasonic-assisted extraction combined with resin purification,and systematically studied the foaming and emulsifying properties of saponins and saponin-protein complexes,to serve the rapid development of X.sorbifolia industry.The main contents and results of this paper were as follows:(1)Preparation of XLs saponins.The effects of ultrasonic assisted ethanol extraction and ionic liquid extraction of saponins were studied,while considering the cost and the requirements of industrial large-scale production,ultrasonic assisted alcohol extraction was used to extract crude saponins;The response surface optimization method was used to optimize the extraction conditions of saponins from XLs,and when ultrasonic power 140 W,time 30 min,temperature 60.8 ℃,ethanol concentration 71.7% and solid-liquid ratio 30.7 m L/g,the extraction yield of saponins reached 7.36±0.078%.The adsorption mechanism of AB-8 macroporous resin on saponins from XLs was investigated.It was found that the equilibrium adsorption capacity of AB-8 resin was higher at lower temperature,and the adsorption process was exothermic.The conditions for purification of saponins by resin were further optimized,and the results showed that the loading amount,concentration,p H,loading rate and elution rate were 100 m L,20 mg/m L,p H 5,2 m L/min,and 2 m L/min respectively,the final purity of saponins was 88.39±2.71%.(2)Study on the foaming and emulsifying properties of saponins from XLs.The obtained results showed that XLs saponins have better foaming ability and foam stability,and resistance to low-p H and high-temperature in compared with lecithin.Physicochemical and rheological measurements showed that the decrease in p H and the increase in temperature could reduce the surface tension and the critical micellar concentration,so that the saponins solution could form micelles and increase the viscoelasticity of saponin solution,and the enhancement of these properties is conducive to the formation of foam with good stability at low-p H value and hightemperature.In addition,the results of particle size and Zeta potential measurements showed the emulsions stabilized by XLs saponins were stable over a range of temperature(30-90 ℃),salt concentration(<100 m M Na Cl)and p H(4-9).Meanwhile,XLs saponins-stabilized emulsion was found to have good storage stability at different temperatures(5,25 and 50 ℃),but the droplet flocculation occurred when they were in a strongly acidic(p H 3)or high ionic strength(300-400 m M Na Cl)conditions.(3)Study on the improvement of foaming and emulsifying properties of whey protein isolate(WPI)by XLs saponins(XLS).It was found that 0.2 or 0.3% XLS significantly increased the particle size and turbidity of WPI solution while reducing protein solubility.Multispectral and determination of protein surface properties showed that the interaction between WPI and XLS resulted in the change of protein structure,significantly improved the surface properties of WPI,and greatly improved the foaming capacity and foam stability of the proteins.The results of rheology and foam microstructure showed that the apparent viscosity and viscoelasticity of WPI solution were significantly improved by adding of 0.3% saponins,and the densest and most uniform foam was formed at p H 3.Moreover,the addition of XLS could reduce the particle size and increase the absolute potential of the emulsion at p H 3.After homogenization,the oil droplets of the emulsion were smaller,and the oxidation stability of WPI emulsion improved obviously.