Study On The Composition And Antioxidant Activity Of Phenols In Different Parts Of Chinese Grapefruit

Citrus paradisi Macf. is one of the major cultivating types of Citrus. It is deeply loved by customers for its special flavor, juicy fruit and abundant nutrition which are both beneficial to our health and complexion. Years of introduction and cultivation have formed some major cultivars with certain planting scale. The phenolic compounds in different fruit parts including flavedo, albedo, segment membrane, juice vesicle and seed of nine grapefruit varieties cultivated in China were determined and their antioxidant capacities were evaluated using DPPH, ABTS, and FRAP methods. The main results have been presented as follows:1、The total phenolic content was between 1.47 and 56.86 mg/g DW and Hongmaxu had the highest content. The total phenolic content in the nine grapefruit varieties were significantly higher compared with the control, and showed significant difference in different fruit parts, which was ranked as:juice vesicle> albedo> flavedo> segment membrane> seed. The total flavonoid content was between 3.85 and 43.75 mg/g DW which was highest in Sibeitimaxu. Compared with the control group, the total flavonoid content in the nine grapefruit varieties were obviously higher and showed significant difference among different fruit parts, which was ranked as:flavedo> albedo> juice vesicle> segment membrane> seed.2、The major grapefruit varieties cultivated in China contained abundant phenolic compounds in fruit. The content of Naringin, a dominant flavonoid observed, was between 0.5293 and 5.6668mg/g DW and was found to be highest in Hongmaxu. The content of tangeretin, a dominant polymethoxyflavone, was between 0.0085 and 3.4360mg/g DW and was found to be highest in Jiwei. The content of Gallic acid, a major phenolic acid, was between 0.0085 and 3.4360mg/g DW and was found to be highest in Sibeitimaxu. The content of phenolic compounds in different fruit parts was significantly different ranked as:albedo> segment membrane>flavedo> juice vesicle> seed.3、Hongmaxu had a rich content of naringin, narintin and nobiletin which was significantly higher than that of other varieties, and also had the highest flavanone content. Jiwei had a rich content of eriocitrin, neohesperedin, sinensetin, tangeretin and ferulic acid which was significantly higher than that of other varieties, and also had the highest polymethoxyflavone content (P<0.05). Sibeizimaxu had a rich content of gallic acid and ferulic acid which was significantly higher than that of other varieties, and also had the highest phenolic content.4、The antioxidant capacities determined using DPPH, ABTS, and FRAP methods were concordant. DPPH of the varieties determined were significantly different. The antioxidant capacities were highest in Huoyan, then Hongmaxu, Maxu, Jiwei, Fenhongtangmuxun, Ruihong and Sibeitimaxu. All the nine grapefruit varieties investigated exhibited higher antioxidant capacities than the control (P<0.05).5、The correlation analysis between phenolic compounds and the antioxidant capacities showed that the content of total phenolic, total flavonoid, hesperidin, neohesperedin, hesperetin, nobiletin, tangeretin and chlorogenic acid had a significantly positive correlation with the antioxidant capacities (P<0.05). It was presumed that hesperidin, neohesperedin, hesperetin, nobiletin, tangeretin and chlorogenic acid might have played very important roles in the antioxidant capacities of grapefruit and that different phenolic compounds might have interactive effects on the antioxidant capacities.In conclusion, the major grapefruit varieties cultivated in China contained abundant phenolic compounds that varied widely among different varieties and different fruit parts. Jiwei, Fenhongtangmuxun, Maxu, Huoyan and Hongmaxu contained more phenolic compounds and exhibited higher antioxidant capacities than control Shatianyou and Liangpingyou pummelos, and were good sources of nutritional quality breeding and natural phytochemical antioxidants.