Study On Separation, Purification And Antioxidant Activities Of Mogroside Compounds From Siraitia Grosvenorii Fruits

Siraitia grosvenorii is one of unique Chinese economic and medicinal herbs. The extraction, purification and analysis of mogrosides from fresh fruits of Siraitia grosvenorii were performed. And the structures and bioactivities of these mogroside compounds were also researched. The major results were as follows:1、Extraction and separation of mogrosidesMogrosides of Siraitia grosvenorii were extracted with aqueous ethanol refluxing. Effects of ethanol concentration, ratio of solvent to material and temperature on the extract yield were determined by single factor experiments and the response surface method respectively, and the optimal extraction conditions were71.16%aqueous ethanol (v/v), material-to-liquid ratio of1:34.65(w/v) and extraction temperature of71.54℃. Under these conditions, the extract yield was9.38%and the extract rate of mogrosides was93.78%.The ethanol extract from Siraitia grosvenorii fruits was further isolated by column chromatography with Macroporous resin LXA-8. The optimum isolation condition was that the ethanol extract was eluted with water and60%ethanol successively at room temperature, and then the60%ethanol elution was collected, concentrated and vacuum freeze-drying. The yield of extract was49.26%, and the yield of mogrosides was73.21%.2、Analysis and determination of mogrosides of Siratia grosvenorii fruitsA high performance liquid chromatographic (HPLC) method for analysis the contents of mogrosides of Siraitia grosvenorii fruits was established. The chromato-graphic analysis was carried out on a Waters SunfireTM C18(4.6mm×150mm I.D.5μm). The column temperature was controlled at25℃, and the mobile phase was0.1%(v/v) phosphoric acid solution (A) and acetonitrile (B) with gradient elution(0-10min:10%-17%B;10-20min:17%B;20-30min:17%-20%B;30-40min:20%B;40-50min:20%-23%B;50-60min:23%B;60-70min:23%-26%B;70-80min:26%B). The detection wavelength was set at203nm, and the flow rate was maintained at0.8mL/min. The results showed that mogroside Ⅱ A2, mogrosideⅢ, mogroside Ⅳ,11-oxe-mogroside Ⅴ,mogroseide Ⅴ and mogrosideVI of Siraitia grosvenorii fruits could be analysed by this method,which had a good linear relationship and precision and high recoveries.The effects postharvest storage time on the contents of main mogrosides in seeds, peel and pulps of Siraitia grosvenorii fruits were studied. The results showed that mogrosides of Siraitia grosvenorii fruits were present mainly in peel and pulp, and the contents of mogrosides were higher in pule than in peel. Among the six analyzed compounds, the content of mogroside Ⅱ A2was the lowest, while the content of mogrosides Ⅴ was the hightest in the freshly picked fruits. With the extension of storage time, the contents of bitter mogrosides reduced and sweet mogrosides increased gradually. Mogrosides ⅡA2in Siraitia grosvenorii fruits was disappeared after7-day storage at room temperature, and the contents of other five mogrosides were increased. After14-day storage, the contents of mogrosideⅢ and mogrosideⅣ were reduced, wheras mogroside Ⅴ and mogroside Ⅵ increased, and the content of11-oxo-mogroside Ⅴ unchanged.3、Isolation and identification of mogrosidesMogrosides were isolated and purified by multistage column chromatography with Macroporous resin LXA-8, silica gel, sephadex LH-20and HP-20SS. The five constituents were obtained successfully and then identified by UV, HPLC and HPLC-ESI/MS/MS respectively. All the results indicated that the five constituents might be mogroside ⅡA2, mogrosideⅢ, mogroside Ⅳ,11-oxe-mogroside Ⅴ and mogroseide Ⅴ.4、Anti-oxidation activities of mogroside compoundsThe scavenging abilities on active oxygen radicals (ROS) of mogroside compounds were studied by chemi-luminescence method. The results indicated that mogroside compounds all had scavenging effects on the ROS, such as superoxide anion radical, hydroxyl radicals and hydrogen peroxide effectively. The crude mogrosides extract showed the remarkable inhibitory effects. The antioxidant abilities of six mogroside compounds were different in different assay systems. The scavenging abilities on superoxide anion radical and hydrogen peroxide from high to low was as follows: mogroside Ⅵ, mogroseide Ⅴ, mogroseide Ⅲ (mogroside Ⅳ),11-oxe-mogroside V and mogroside ⅡA2, and the scavenging abilities on superoxide anion radical of the six mogrosides was: mogroside Ⅱ A2>mogroside Ⅵ>mogroseide Ⅴ>mogroseide Ⅳ mogrosideⅢ>11-oxe-mogroside Ⅴ.