| China has been recognized as the main origin centre for the genus Citrus L., and is rich in variety resources. China has witnessed a had ripid development in citrus industry in the last20years; in2010, cultivated area of citrus was2.212million hectares and the total production was26.45million tons, all ranked first in the world. Citrus fruits are rich in nutrition and bioactive compounds such as flavonoids, so it’s an important plant source of extracting and producting natrural bioactive compounds. Pummelo originated from China and there are many natural hybrids and breeding varieties of pummelos. Bioactive compounds (phenolic acid%flavonoids et al.) in pummelo fruits are rich, and the flavonoids were proved to have bioactivities and healthy promotion values. Determination of flavonoids, together with the evaluation of activity are the current research focuses, but the systematic study of flavonoids in fruits of pummelo and pummelo hybrids has not been reported. Determination of flavonoids types and contents in pummelos fruits, analyzing the correlation bewteen antioxidant activity and flavonoid content by application of modern analytical instrument and in vitro antioxidant activity evaluation methods could provide guiding significance for establishing flavonoids database of pummelos grown in China, discovering of special citrus fruit resources that abundant with flavonoids and comprehensively using and developing of citrus germplasm.In this work, the flavonoids composition in the fruits at different manturity periods of32pummelo and grapefruit varieties and2pummelo hybrids cultivated at the National Citrus Germplasm Repository (NCGR) were analyzed using Ultra Performance Liquid Chromatographic (UPLC), and the in vitro antioxidant activities of fruits extracts were determined to evaluate antioxidant capacity, and then take data statistical analysis. An optimized method for separation and quantification of citrus flavonoids was also established, flavonoid contents and antioxidant capacity of different fruits tissues of each variety at different maturity periods were analysed, and correlations of flavonoids, fruit quality and citrus varieties, flavonoids genetic mechanism were also primarily analysed. The results as fallows:(1) The UPLC method for the quantification of flavonoids in citrus fruit was developed in this work,11selected flavonoids were separated in11min. The separation was carried on a ACQUITY UPLC BEH C18(2.1mm×100mm,1.7μm, column temperature35℃).Methanol (A)/0.1%formic acid/water (B) mixture was used as the mobile phase at a flow rate of0.3mL/min through gradient elution ((1)0-5min,90%-80%A;(2)5-10min,80%-30%A;(3)10-15min,30%-20%A;(4)15-16min,20%-90%A.), column temperature:35℃; flow speed:0.3mL·min-1.11flavonoids were completely separated in11min, resolution R between in1.80-7.02, the LOD of flavonoids between in0.05-0.13ug/mL, and LOQ is0.08-0.35μg·mL-1, RSD is0.89%-5.93%, recovery rate between in85.4%-114.0%. This method is rapid, accuracy, high sensitive, and low consumption of organic solvents.(2) The flavonoids of32varieties of pummelo and grapefruit,2pummelo hybrids fruits were identified and quantified at different maturation stages. The results shown: Flavonoids are abundant in pummelo and grapefruit fruits, the flavonoids contents are higer in the peels than in the pulps, and the flavonoids contents in immature fruits were higher than that in mature fruits. Five of eleven flavonoids (eriocitrin, narirutin, naringin, neohesperidin, didymin, naringenin) was detected in most of pummelo fruits while ten of eleven (eriocitrin, narirutin, naringin, hesperidin, neohesperidin, didymin, naringenin, hesperitin, nobiletin, and tangeretin) was in grapefruits. The highest naringin content was detected in Rio Red,23377.61mg/kg in peel at immature period (Jun25),9871.69mg/kg in peel and4166.19mg/kg in pulp at mature period (Oct25); Neohesperidin was highest in Cock Tail peel (12828.41mg/kg) at immature period and highest in Cock Tail peel (7011.15mg/kg) and Changshan-huyou pulp (3121.72mg/kg) at mature period. The flavonoids kinds was most in Huayingshanyou peel among pummelos fruits,9flavonoids were detected at immature periods. Also9flavonoids were detected in the fruits of hybrid ZhikexShatianyu and narirutin content was highest, respectively were in peel (9020mg/kg), pulp (1240mg/kg); the flavonoids types and content of DianjiangbaiyouxShatianyu fruit was similar to pummelos, so the flavonoids composion of hybrids fruits maybe affected by parents especially father.(3) In vitro antioxidant activities of32varieties fruits extracts were determined, the evaluate methods were DPPH, ABTS and Fenton method. The capability of scavenging ABTS-was highest in three methods. The antioxidant capacities of immature peels were higher than those of mature peels; the antioxidant capacities of peels were significantly higher than those of pulps at mature period. The capability of scavenging DPPH·was high in32varieties, the values were32.33-65.21VCE/100ml at immature period and31.93～55.53VCE/100ml at mature period; the capability of scavenging ABTS·was highest in Huayingshanyou both immature and mature periods, respectively were83.40%、82.51%; the capability of scavenging OH·were higher in3grapefruits, by synthetical analyized of results of3methods, Rio Red, Cock Tail, Changshan-huyou and Huayingshanyou peels extracts have higher scavenging free radicals capabilities and higher antioxidant activities.(4) The total sugar, reducing sugar, sucrose, titratable acid, and vitamin C of32pummelo and grapefruit fruits were assay, and principal component analysis was used. The results shown, compared to other citrus varieties the sugar contents in pummelo fruits were higher, the titratable Acid contents were lower than, and the Vitamin C was abundant; the total sugar were highest in Guanximiyu and Dongfengzao (10.70g/100g), the titratable acid were higher in3grapefruit fruits, and vitamin C was highest in fruit of Cock Tail grapefruit (105mg/100g). Correlation analysis showed there was positive correlation between flavonoid, vitamin C contents and antioxidant activities... |
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