| Total of alfalfa saponins(TAS)is an important component in medic plant,which may be biologically active in reducing plasma cholesterol and guarding against atherosclerosis in recent years and possessing medicinal value and developing prospect. The research studies the extraction , purification and its biological activity, which is Medicago sativa L as the raw material, in order to privideing foundation for further development and utilization.The major results are shown as follow: the content of TAS was determined by UV-VIS spectrophotometry after it has been colored. Using Oleanolic Acid as a standard substance, assured detective wavelength of TAS was 560nm and standard curve equation was y=0.1453x-0.0071, relative coefficient R2=0.9993,the average recovery was 98.3% with RSD of 3.88%.The method is rapid, accurate and repeatable.Different methods of extracting on total saponins from alfalfa were studied. (1)Ethanol solution extraction. The result shows that technological parameter of extraction rates of TAS is the best when soaking solution contain 70% ethanol, at 80℃, for 1.5h, with the solid liquid radio of 1:20.The average extracting rate of TAS is 1.472%,RSD(%)=1.58%.(2) Ultrasonic extraction. The extracting rate of TAS is 2.025% under the condition with soaking solution contain 70% ethanol, ultrasonic treatment time of 10 minutes, the solid liquid radio of 1:10, with RSD(%) of 4.19%.The ultrasonic extraction rate of ethanol solution is higher 37.57% than normal ethanol solution extraction, and proved that the method of ultrasonic extraction is efficiently and feasible.The separation and purification of TAS were carried out with the method of macroporous adsorption resin. The investigation indexes are static adsorption quantity, eluting rate and refined rate, studying the absorption and desorption of TAS on it. The result indicated that DM-130 of low-polarity macroporous resin fits for the separation of TAS on it, the optimal purification parameter of DM-130 were: pH of 5, flowing rate of adding sample 2BV/h and adsorption solution 2BV/h.It was confirmed that the best operational condition was: the original concentration of the TAS solution 8~12mg/mL, radio of diameter to height of the chromatographic column 1:8.It is desired to elute with water volume 4BV, flowing rate 2BV/h, then desorpting with 4BV alcoholic solution at the same flow rate, to effectively separate TAS.The biological active of TAS was proved by initial trial on antioxidant capability outside body. (1) Reducing capacity experiment. It proved that TAS has the biological active of clearing free radical and the magnitude of the reducing capacity is linear correlation to the concentration of TAS. (2)TAS has the active of clearing DPPH free radical, different concentration TAS has different clearing capacity, and the concentration to clearing capacity shows linear relative.According above all, using ultrasonic technology assisting ethanol extraction, utilizing macroporous resin purificating TAS, these methods and technology can raise extraction ratio and purity coefficient of TAS effective. Through the trial of reducing capacity and clearing DPPH free radical, initial proved that the TAS has the capacity of clearing free radical.
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