| Citrus is one of the biggest yield fruit in China, which is processed for can or juice in industrial production and lots of citrus by-products are produced. There are 20 percent of citrus by-products produced to pericarpium citri reticulatae and most of the rest are carried to landfills, however, there are many bioactivities in the citrus peels, such as citrus essential oils, flavones, carotenoids and limonin. Polymethoxyflavones has been drawn more and more attention for its special flavones in the citrus peel. Research shows that polymethoxyflavones possesses anti-inflammatory, anti-cancer, anti-atherosclerotic, anti-oxidant activities. So it is of great importance for food, drug and health care industry to extract and separate efficiently and synthesize the polymethoxyflavones.This paper is aimed at extracting the polymethoxyflavones from the kiyomi tangor peels, comparing the content of polymethoxyflavones of different citrus peel and different polar extracted parts, analyzing the rate of conversion of hydroxyl polymerhoxyflavones in the citrus peel, preparing the polymethoxyflavones from the citrus peels by the mean of column chromatography and HPLC, synthetizing two 5-hydroxyl polymethoxyflavones and measuring the antioxidant activity of nobiletin,5-hydroxyl nobiletin, tangerine,5-hydroxyl tangerine. And the results are as follows:(1) The optimal method of ultrasonic extraction for polymethoxyflavones in Kiyomi tango peels is ethyl acetate as solvent, liquid to material ratio 1:30, ultrasonic time 30 min and twice extraction, while the optimal method of reflux extraction is ethyl acetate as solvent, liquid to material ratio 1:30, reflux time 4 h and twice extraction. The result is that reflux extraction is better than ultrasonic extraction. Hydroxyl polyethoxyflavones in citrus peels mainly produce at 5 position in A ring of benzo-y-pyrone skeleton, hydroxyl polyethoxyflavones in tangerine peels ars mainly 5-hydroxyl nobiletin (141.39±1.84μg/g),5-hydroxyl tangeretin (19.67±1.24μg/g), 5-hydroxyl sinensetin (13.98±2.24μg/g), and 5-hydroxyl-3,6,7,8,3’,4’-hexamethoxyflavones (4.95±1.08μg/g) with their conversion rates of 1528%,3.87%,39.12% and 17.15% respectively, which are higher than those in mandarine and orange peels. However,5-hydroxyl sinensetin in mandarine peels and 5-hydroxyl tangeretin in orange peels are not detected.(2) Ethyl acetate extracts of Kiyomi tango peels are separated on column chromatography eluted with two differnet elution systems, methylene chloride-methanol (100:1,90:1,80:1, 70:1,60:1,50:1,40:1,30:1,20:1 and 10:1) and N-hexane-ethyl acetate (10:1,9:1,8:1,7:1, 6:1,5:1,4:1,3:1,2:1,1:1 and pure methanol). The separation effect of N-hexane-ethyl acetate system is better than that of methylene chloride - methanol, with the enrichment of polymethoxyflavones in the 1:1 and pure methanol fractions. Eventually, the main polymethoxyflavones are obtained by semi-preparative HPLC.(3) Nobiletin and tangeretin are refluxed respectively at 72 h,90 ℃ in 3M HC1 and methanol, then 5-demethynobiletin and 5-demethytangeretin are obtained. The antioxidant activities of four polymethoxyflavones are compared. The radical scavenging abilities of 5-hydroxyl polymethoxyflavones are slightly higher than their parent compounds or are equal to their parent compounds in ABTS and DPPH free radical scavenging abilities test. 5-hydroxyl polymethoxyflavones containing hydroxyl groups are unexpected to have lower antioxidant activities, which might be related to form intramolecular hydrogen bonds between hydroxyl group in 5 position and keto group in 4 position. |
PDF Full Text Request