Study On The Extraction And Antioxidation Property Of Total Flavonoids From Rudbeckia Hirta Petals

Rudbeckia hirta is cultivated widely, which belongs to Chrysanthemum plant. In this paper, the optimum extraction conditions of flavonoids from Rudbeckia hirta petals were studied by ultrasonic-assisted extraction. The flavonoids which were extracted from Rudbeckia hirta petals were isolated and purified with silica gel chromatography. The antioxidant activities of flavonoids from Rudbeckia hirta petals were evaluated by four methods which were K3Fe(CN)6method for measuring reducing activity, DPPH radical quenching, hydroxyl radical and superoxide anion radical scavenging method, respectively. The experimental results were as follows:1. The extraction technology of total flavonoids from Rudbeckia hirta petals was optimized using ultrasonic-assisted extraction. The optimum technology by single factor experiment was as follows:ethanol concentration70%, ratio of liquid to material20:1(mL/g), extraction time50min and temperature50℃.2. The parameters of extraction technology were optimized by response surface methodology. With the yield ratio of total flavonoids as response value, the interaction of the three variables (including ethanol concentration, ratio of liquid to material and extraction time) and their influence on the extraction rate were studied by using Box-Benhnken central composite design theory. Under the condition of temperature50℃,the optimum technology by response surface methodology was as follows:ethanol concentration71%, ratio of liquid to material22:1(mL/g) and extraction time52min. Under these conditions, the average yield ratio of total flavonoids was4.719%, which was very close to the predicted data (4.721%).3. The ethanol extractions from Rudbeckia hirta petals were extracted with petroleum ether, chloroform, ethyl acetate and n-butanol successively, and then the extractions were evaporated in vacuum. The crude ethyl acetate extracts were repeatedly subjected to silica gel chromatography with chloroform-methanol-methyl acid as eluents and followed by TLC to obtain three compounds. The isolated flavonoids were identified by1H-NMR,13C-NMR and HMBC spectroscopic techniques, they were Eupatolitin3-O-β-D-(6"-O-acetyl)-glucopyranoside (Ⅰ), Eupatolitin (Ⅱ), Eupatolitin3-O-β-D-glucopyranoside (Ⅲ) respectively. All the compounds were first found from Rudbeckia hirta petals, and compound I was a new compound which was first isolated.4. With Vitamin C as reference compound, the reducing activity of all the extractions was measured by K3Fe(CN)6method. And the antioxidant activities of all the extractions and compounds were evaluated by measuring their ability to scavenge the DPPH radical, hydroxyl radical (OH) and superoxide anion (O2-·).The results showed that all the extractions had certain reduction ability. The ethyl acetate fraction and n-butanol fraction were shown to be the most potent antioxidants. The antioxidant activities of compound I and III were also very high.