| Citrus is a major fruit in China. Its peel is a high valuable source, being rich in essential oils, pects, flavonoids, etc. However, the application of citrus peel as a byproduct from citrus processing industry isn’t quantificationally utilized, being a waste of high quality source.In this work, systematic studies of citrus flavonoids were carried out on the extractional technology, isolation, purification, identification, quantification, antioxidant activity, [OH] scavenging activity, restraining tumour cell and diabetes activity, and chemic modification. This study was also undertaken to investigate on the amino acids, essential oils from citrus peel. The main results are as follows.Amino acids of protein in citrus peel were analysed by automatic technology. Protein content of citrus peel(dry substance) is 3.45% (m/m), concluding 1.34% essential amino acids. Essential amino acids of protein is 35.96%, less than which of soybean protein, Met and Cys-s are limited amino acid in citrus peel.Fatty acids and volatile compounds in honeyorange peel were separated and identified by GC-MS.13 fatty acids identified in citrus peel oil consist of 6 saturated fatty acids (27%) and 7 unsaturated fatty acids (66.62%). The saturated fatty acids is mainly composed of hexadecanoic acid (19.75%). The unsaturated fatty acids are mainly composed of linolenoic acid (19.06%) and linoleic acid (37.14%). And 42 components were identified. It was found the main components were Isolimonen (25.92%),2-(1-Methylethylidene)-bicyclo[2,2]heptane (19.82%), 4-Methyl-1-(1-methylethenyl)-cyclohexene (15.81%),2-Ethyl-1-octen-3-yne (9.20%), Beta-myrcene (8.59%)、(E)-3,7-Dimethyl-1,3,6-octatriene (6.41%). The volatile components identified is 98.77% in volatile compounds.The kinds and polarity of flavonoids were ananlyzed by HPLC and UV. Testing results showed that there about twenty-five kinds of flavonoids in honeyorange peel.In order to effective extract flavonoids from citrus peel, ultra-sonic wave-assisted extraction technique of total flavonoids from citrus peel was studied according to a current, rotational and combinational design of quadratic regression.Then, one quadratic regression model for the total flavonoids yield was established, the extraction conditions were optimized by using above model and the optimized results were verified by experiments.Results shows that the pH value had a very significant effect on the extraction rate of total flavonoids. Ethanol concentration,the ratio of solution to material and the interaction between time and ethanol concentration, also time and pH value had significant effects on the extraction rate. Extraction time had no significant effects on the ex-traction rate. Research results indicate that the optimized extraction conditions for obtaining maximum yield of total flavonoids are pH value 5.6, ethanol concentration 75%, ratio of solution to material 26, extraction time 80 minutes.Under the optimized conditions, the experimental value of yield was(3.314±0.163) %(n=3),which was close to the estimated value 3.348% attained by using regression model.The model for the total flavonoids yield have better prediction effects.Five flavonoids monomers were purifed with Silica gel, Polyamide, Sephadex LH-20 columns and their structure were determined by LC-MS,1H-NMR, 13C-NMR, and IR. The five compounds were shown as follows:compound A (3,5,6, 7,8,3’,4’-Heptamethoxyflavone); compound B (5,6,7,8,4’-Pentamethoxflavone) compound C (3-hydroxy-5,6,7,8,3’,4’-hexamethoxyflavone); compound D (5,6,7, 8,3’,4’-hexamethoxyflavone); compound E (Hesperidin). Compound C seem to be previously unreported in citrus peel.The antioxidant properties were investigated by ferric thiocyanate method and phospholipids peroxidantion in liposome. The results showed that five flavonoids were able to inhibiting linoleic acid peroxidation, compound D is strongest in inhibiting linoleic acid peroxidation, followed by compound C, similar to Quercetin, compound B and compound A sequently. Compound E is worst, slightly better to rutin. The inhibiting capacities of flavonoids to conjμgated diene hydroperoxide during liposome oxidation were in the following order:compound D>compound C>compound B≈Quercetin> compound A> compound E> Rutin.Their half-inhibition concentration (IC50) to phospholipids peroxidation are 3.11μg/mL for compound A,2.65μg/mL for compound B,0.96μg/mL for compound C,0.35μg/mL for compound D,3.52μg/mL for compound E. The antioxidant activities increased significantly with their increasing concentration.The physiological functions of scavenging [·OH] were also investigated. Among the five mononmers, the capacities of compound D scavenging [·OH] was the strongest, IC50 was only equal to 3.2μg/mL, while IC50 of other compounds were 5.6μg/mL for compound C,9.6μ.g/mL for compound B,11.5μg/mL for compound A,13.6μg/mL for compound E.MTT and PTP1B model were employed, the capacities of inhibiting tumour cell growth and diabetes were investigated. The result showed that compound D and compound B were effect on inhibiting tumour cell growth, others compounds is no effect. And five flavonoids have no effect on inhibiting diabetes.Five Bioactive flavonoids persicogenin, luteolin,7-O-isopentenyl hesperietin, 7-O-farnesyl hesperietin and 7,3’-O,O-difarnesyl hesperietin were synthesized by reacation steps including glycoside hydrolysis, selective methylation, dehydrogenation, demethylation, O-prenylation and O-farnesylation respectively. The overall yields were 60%,39%,64%,16% and 15% respectively calculated from hesperidin as the starting material, Their structures were confirmed by NMR, IR and mass spectra. The synthetic methods have the advantages of starting materials obtained easy, simple operation and good yields. So it has considerable practical value. |
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