Rhubarb Extracts By Anti-oxidative Activity And Chemical Composition

Rhubarb,a well-known Chinese herbal medicine,has long been used in oriental preparations and is officially listed in Chinese Pharmacopoeia. This important herbal medicine was recognized for centuries in traditional medicine for its multiple pharmacological actions including laxative,antibacterial,hemostatic,antitumon.The major active components of this herb are five anthraquinones(AQs),namely aloe-emodin,rhein,emodin,chrysophanol and physcion.However,a few studies on the correlation between antioxidant capacity of Rhubarb and the contents of antioxidant were reported.So it has great potentiality to be exploited.The primary purposes of this work are to use hyphenated instrument(eg.HPLC-DAD) and chromatographic pharmacodynamics of TCM to predict antioxidant capacity of Rhubarb by chemometric approaches.In this thesis,the following contents are included:1.In the introduction part of this thesis,the antioxidant and free radical,the development of natural antioxidants,the traditional Chinese medicine Rhubarb,chemometric methods with their application to TCM and chromatographic pharmacodynamics of TCM are summarized.2.DPPH free radical scavenging activity was used for characterization of antioxidant activity of extracts of the traditional Chinese medicine Rhubarb.Extracting conditions were optimized through a series of comparative researches on the influences of solvent types,ethanol concentration,extracting time,the ratio of solid to liquid and extracting times.The optimum ultrasonic extraction conditions were obtained as follows:using 70%EtOH as extracting solvent,the sample was extracted twice and each time for 20 minutes,when the ratio of solid to liquid was 1:30(g/mL).The experimental results showed that the extracting efficiency of ultrasonic method was 95.2%in scavenging rate on DPPH·and much better than those of maceration and reflux extraction.3.A reversed phase high performance liquid chromatography (RP-HPLC) method was developed for the simultaneous determination of five anthraquinone derivatives(aloe-emodin,rhein,emodin, chrysophanol and physcion) in rhubarb,to optimize the ultrasonic extraction conditions.The linearity ranges of the five free anthraquinones were wide,showing good lineal correlations with correlation coefficients (R~2) of 0.9987 to 0.9997.The average recoveries were from 92.79%to 99.28%.While the intra-day and inter-day precision were 0.65%～1.71% and 2.52%～3.46%,respectively.4.Partial least squares(PLS) was employed to build the correlation model between DPPH free radical scavenging activity and the contents of five free anthraquinones determined by RP-HPLC,and to predict the DPPH free radical scavenging activity of extract from Rhubarb.The other model was built by PLS to predict the antioxidant capacity of Rhubarb from chromatographic fingerprints.Compared with the model using chromatographic peak area,the model from the entire chromatographic profiles reserving the information of all the components obtained better prediction with objective data analysis.