| Ginsenosides are the mainly effective components in the plants of Araliaceae, Panaxgenus, including Panax ginseng C.A. Meyer, Panax quinquefolium L. and Panaxnotoginseng (Burk.) F.H. Chen etc. It is reported that ginsenosides have manypharmacological activities, such as immunoenhancement, antifatigue, antineoplastic,anti-hypoxia, anti-aging and anti-hyperglycemic etc. Ginsenosides can be classified as majorginsenosides and rare ginsenosides. The major ginsenosides, including protopanaxadiol–typeginsenosides Rb1, Rb2, Rb3, Rc, Rd and Protopanaxatriol-type ginsenosides Re and Rg1, arethe ginsenosides that have high contents in herbs of Panax genus and can be easily separatedand purified. The rare ginsenosides are secondary ginsenosides which can be obtained frommajor ginsenosides by the manner of deglycosylation or structure changes in side chains.Most of the rare ginsenosides, including ginsenoside Rh1, Rh2, Rh3, Rg3, Rg5, Rg6, Rk1, Rk3,Rh4, F4, Rc-k etc., have low contents or can’t be detected in herbs of Panax genus. In recentyears, researches in bioactivities of rare ginsenosides have made significant progress. Lots ofresearches indicated that rare ginsenosides have higher pharmacological effects onantineoplastic, antifatigue and free radicals scavenging activities than major ginsenosides.As the discoveries of new bioactivities of rare ginsenosides, how to obtain rareginsenosides fast and efficiently is one of the hotspot issues in current researches ofginsenosides. Conventional methods of extraction and isolation can only get majorginsenosides from herbs of Panax genus. Major ginsenosides can converted to rareginsenosides by acid, alkaline, enzymatic degradation or high temperature and high pressureprocess etc., but there are disadvantages such as low yields, difficulty of separation andpurification. So it’s hard to obtain high-purity rare ginsenosides monomers massively by themethod mentioned above. Microwave, which was applied to the extraction of components of traditional Chinesemedicine, could brought the non-thermal effects in the increasing the extraction efficiency forthe experiment system at the same time. Under the effects of microwave electromagneticfield, polarization phenomenon of molecules in this system occurred. Meanwhile，microwaveintensified the frequency of vibration and rotation of molecules and made the moleculesin hyperactive metastable state, which led to the break and recombination of weak chemicalbonds. Moreover, intensification of thermal motion of molecules greatly increased thefrequency of effective collisions between molecules, which promoted chemical reaction rate.Chemical structures of constituents in samples which processed by microwave are prone tochanges. Glycosidic bonds or parts of the weak chemical bonds of side chains in ginsenosideseasily broke and recombined in microwave field. So it was possible to accelerate theconversions from major ginsenosides to rare ginsenosides by using microwave technology.In this article，we deeply studied the degradation effects and mechanisms of7majorginsenosides and Panax quinquefolium L. by using microwave technology, and thehypoglycemic and antioxidant bioactivities of degradation products were tested, andcompared with the extracts by traditional method simultaneously.At first we determined9kinds of rare ginsenosides in degradation products including20(S)-Rh1,20(R)-Rh1, Rg6, F4, Rk3,20(R)-Rg3,20(S)-Rg3, Rk1and Rg5by high performanceliquid chromatography for quantitative analysis after microwave-assistant degradation. Thenwe investigated the optimum microwave assisted degradation conditions, considering theyields of rare ginsenosides as the indicator. The factors including the extract solution,material ratio, extract time, temperature and microwave power etc. were investigated. Theresults showed that when extracted the samples with water, kept temperature at145℃for15min with the solvent volume ratio of40:1(V/W) and controlled the microwave power at1600w, yields of different ginsenosides almost reach the maximum. In addition, we comparedthe differences between the microwave-assistant degradation and conventional reflux heatingextraction method, the results indicated the great promotion effects on conversions of majorto rare ginsenosides by microwave-assistant degradation method. Major ginsenosides of Panax quinquefolium L. can completely convert to rare ginsenosides in microwave-assistantdegradation method, while it was not obvious of that in conventional reflux method.In this article we made degradation of7kinds of major ginsenosides includingginsenoside Rb1, Rb2, Rb3, Rc, Rd, Re and Rg1under the optimal condition ofmicrowave-assistant degradation method. Comparing with microwave-assistant method, thedegradation products were obtained by using high temperature and pressure under the samecondition except for the existence of microwave also. The results of experiment indicated thatthere was significant promotion effect on conversion of ginsenosides from major to rare onesby microwave-assistant degradation method.On the basis of the researches above, the article concluded the mechanism of conversionfrom major ginsenosides to rare ginsenosides during microwave-assistant degradation. Itindicated that rare ginsenoside Rg5had the highest contents among the degradation productsof5kinds of protopanaxadiol–type ginsenosides. The other yields of rare ginsenosidesconformed to the order of Rk1＞20(R)-Rg3＞20(S)-Rg3. Two kinds of the major ginsenosidesof the protopanaxatriol–type group showed differences in rare ginsenosides of degradationproducts. Although rare ginsenoside Rh4had the highest contents among ingredients ofdegradation products, the other yields of rare ginsenosides in degradation products ofginsenoside Re conformed to the order of Rh4＞Rk3＞F4＞20(R)-Rh1≈20(S)-Rh1＞Rg6，while it showed the order of Rh4＞Rk3＞20(R)-Rh1＞20(S)-Rh1in the degradation productsof ginsenoside Rg1.The article finally compared the bioactivities of degradation products of Panaxquinquefolium L. and major ginsenosides, which processed with or withoutmicrowave-assistant method.The article investigated protective effects on different extract and degradation productsby using the AAPH induced erythrocyte hemolysis model. The extract products are theextract of Panax quinquefolium L.by using conventional methods and the degradationproducts are Panax quinquefolium L. and7major ginsenosides by using microwave-assistantor by using high temperature and pressure methods, respectively. The results demonstrated that in low concentration, extract or degradation products of Panax quinquefolium L. hadcertain protective effect on free radical induced oxidative erythrocyte hemolysis.Microwave-assistant degradation products showed the highest activity, among which theactivity order was degradation products of microwave-assistant method>high temperatureand pressure method>methanol reflux extraction>water reflux extraction. But in highconcentration, products mentioned above showed promotion of erythrocyte hemolysis.The Inhibitory effect of microwave-assistant degradation products of7kinds of majorginsenosides on erythrocyte hemolysis had the relationship of Rd>Rc>Rb3>Re~Rg1>Rb2~Rb1, while the order of Inhibitory effect of that by high temperature and pressure methodwas Rg1>Re>Rd>Rb1~Rb2~Rc>Rb3. The relation of Inhibitory effect onerythrocyte hemolysis was presented as degradation products of microwave-assistantmethod>high temperature and pressure in low concentration. But it was just opposite whenthe products were in high concentration.The article also studied on the anti-hyperglycemic effect of31kinds of samples includingdegradation products of roots and leaves of Panax quinquefolium L., degradation products of7kinds of major ginsenosides, reflux extract products of roots and leaves of Panaxquinquefolium L. and the degradation products of the roots and leaves of Panaxquinquefolium L. processed by microwave or high temperature and pressure method. Wedetected the inhibition rate of samples to DPP-Ⅳ. The system was reacted under theconditions of0.8U/L DPP-Ⅳ and0.5mmol/L substrate respectively, reaction time1.5h, at37℃and pH of8.0. After detecting the absorbance of the reaction system at405nm withELIASA, inhibition rate was calculated with formula. The results indicated that products ofPanax quinquefolium L. including that obtained via microwave or high temperature andpressure method had little Inhibitory effect, except methanol and ethanol reflux extractproducts which had certain but weak effect. Major ginsenosides also showed little Inhibitoryeffect on DPP-Ⅳ, but the degradation products of major ginsenosides processed withmicrowave-assistant or high temperature and pressure method showed certain Inhibitoryeffect on DPP-Ⅳ. Degradation products of ginsenoside Rc and Rd subjected with microwave-assistant method and that of ginsenoside Rb2and Rc processed with hightemperature and pressure method had relatively obvious Inhibitory effect on DPP-Ⅳ amongthe31samples.In conclusion, the results of experiments in the article indicated that microwave-assistantdegradation method was an effective method converting major ginsenosides to rare ones.Bioactivities researches in vitro demonstrated that rare ginsenosides obtained bymicrowave-assistant degradation method may have obvious effects on anti-oxidation, freeradicals scavenging and reducing blood glucose. The results of the research showed that wecan obtain more strong bio-active degradation products from ginsenoside monomers bymicrowave-assistant degradation method, and also we can obtain the extracts from the plantsof Panax genus by microwave-assistant extract method. Meanwhile, the paper providednew thoughts and research methods of getting components with stronger bioactivity fromChinese traditional medicine by microwave-assistant degradation method. |
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