Microwave Degradation Of Ginsenosides In Extract From Panax Quinquefolium L. Leaf

The root of Panax quinquefolium L. is a typically source for use in many traditional medicinal therapies. Compared with the root, the leaf was less investigated. Annual recovery of ginseng leaf could be a feasible alternative source of ginsenosides compared with the roots requiring the long growth cycle for nutritious products. It was found that the content of total ginsenosides in leaf is much higher than that in root. The leaf of Panax quinquefolium L. is a source of ginsenosides but has not been well exploited up to now.Rare ginsenosides, including Rg2,Rg3,Rg5,Rh1,Rh2,Rh3 and Rck, can be obtained from deglycosylation of the major ginsenosides. Compared with the major ginsenosides, rare ginsenosides have higher bioactivity and many researches indicated that the metabolites of major ginsenosides in vivo and in vitro which belong to rare ginsenosides are the bioactive compounds. Among the rare ginsenosides, Rg3 and Rh2 are of greatest interest because their bioactivity is higher than others especially in the aspect of anti-tumor. It has been reported that ginsenoside Rg3 is metabolized to ginsenoside Rh2 and 20(S)-protopanaxadiol when anaerobically incubated with human fecal microflora, and the activities of deglycosylated metabolites are comparable to or higher than that of Rg3. Characteristics and mechanism of effects among the three one have been proved similar, but the sequence of functional strength is 20(S)-protopanaxadiol, Rh2 and Rg3, which probably has close relation with that 20(S)-protopanaxadiol is the aglycone of Rg3 and Rh2. Thus, preparation and determination of Rg3, Rh2 and 20(S)-protopanaxadiol are singnificant for their biological and pharmacological activities.In this thesis, based on the summary of the chemical constituents, pharmacology, degradation methods of ginsinosides, the microwave degradation of ginsenosides in extract from Panax quinquefolium L. Leaf was studied. Due to the importance and the low content of rare ginsenosides in the Panax quinquefolium L., the microwave irradiation coupled with foam floatation were developed to obtain the rare ginsenosides. Both foam floatation and degradation conditions were investigated and optimazied.Neutral solution, acidic solution, alkaline solution and N, N-dimethylformamide (DMF) were used as degradation media in the degradation of ginsenosides obtained from leaf of Panax quinquefolium L., respectively. This method is based on the separation of ginsenosides present in the degradation products using high-performance liquid chromatography (HPLC), followed by detection with atmospheric pressure chemical ionization mass spectrometry (APCI/MS). Four degradation media were compared in terms of the degradation time, temperature, yields of rare ginsenosides. The results indicated that ginsenosides Rg3, Rh2 and aglycone are not naturally present in Panax quinquefolium L., but are the products obtained simultaneously in the microwave irradiation degradation process. The yield of Rg3 is 7.69mg/g and 250 times as high as that obtained from red ginseng. It is important to stress that a new degradation medium, N, N-dimethylformamide, was discovered and when the medium was used, the transformation rate of total ginsenosides to rare ginsenosides is 20.20%. The results indicated that the optimal condition of degradation to prepare 20(S)-protopanaxatriol was that the water solution adding sodium hydroxide (0.5 mol/L) was heated up to 165°C for 5 minutes. The transformation rate of total ginsenosides to rare ginsenosides is 78.11%.The results indicated that ginsenosides Rg3, Rh2 and aglycone are not naturally present in Panax quinquefolium L., but are the products obtained simultaneously in the microwave irradiation degradation process. The proposed method is simple, efficient, time saving. Compared with the traditional degradation methods, such as acidic hydrolysis, alkaline degradation, enzymatic conversion and microbial degradation, some performances for degradation of ginsenosides were improved when the proposed method was applied.