Abstract: 【Objective】 The polyphenols in grapefruit (Citrus paradis Macfad.) of different varieties were identified and characterized. The antioxidant activities of polyphenol extracts from different samples of each variety were compared. The aim of the study is to obtain the scientific data for improvement of Citrus breeding, grapefruit resources development and utilization. 【Method】The composition and content of phenolic compounds in pulps of nine major grapefruit varieties cultivated in China were determined by High Performance Liquid Chromatography (HPLC), and the antioxidant activities of these grapefruits were evaluated by using 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH), ferric reducing antioxidant power (FRAP), and 2,2′-azino-bis (3-ethylbenzthiozoline- 6)-sulphonic acid (ABTS) methods. The correlation between antioxidant capacity and phenolic content was measured with Pearson correlation coefficient. 【Result】 Results showed that naringin and neohesperedin were the predominant flavanones in grapefruit, the naringin contents varied from 1 180.58 μg·g^-1 to 3 065.33 μg·g^-1, Huoyan had the highest content of naringin, while neohesperedin contents varied from 94.05 μg·g^-1 DW to 637.24 μg·g^-1 DW, Jiwei had the highest content of neohesperedin. Tangeretin was the major polymethoxylated ?avone, varying from 0.56 μg·g^-1 DW to 4.66 μg·g^-1 DW, which reached the highest content in Aoluobolangka, and gallic acid was the major phenolics acid, varying from 60.42 μg·g^-1 DW to 385.53 μg·g^-1 DW, which reached the highest content in Sibeitimaxu. Jiwei was rich in eriocitrin (111.23 μg·g^-1 DW), while Maxu rich in hesperidin (130.90 μg·g^-1 DW). Huoyan, Ruihong, Sibeitimaxu, and Hongmaxu had abundant gallic acid (＞300 μg·g^-1 DW), whereas Jiwei contained rich chlorogenic acid, caffeic acid and ferulic acid. The overall antioxidant potency composite index (APCI) revealed wide variations in the grapefruits investigated (36.70-97.50). Except for Aoluobolangka and Jiwei, the other seven grapefruit cultivars presented high APCI (＞80). Naringin, neohesperedin, hesperetin, nobiletin, tangeretin and chlorogenic acid showed a significant positive correlation with antioxidant abilities. 【Conclusion】 The pulps of nine major grapefruit varieties cultivated in China were rich in polyphenols. Different varieties showed obvious variations and characterized by their composition and content of phenolic compounds. Naringin, tangeretin and gallic acid were the predominant phenolic compounds of nine grapefruit varieties studied. Significant variations in polyphenols contents and antioxidant abilities were found between the tested varieties. Huoyan, Ruihong, Sibeitimaxu and Hongmaxu are good natural source of gallic acid, while Jiwei is the natural source of chlorogenic acid, caffeic acid and ferulic acid. Among the nine grapefruit varieties investigated in the study, Fenhongtangmuxun, Maxu, Huoyan, Ruihong, Sibeitimaxu and Hongmaxu not only contained rich phenolic compounds, but also presented high antioxidant activities. It was concluded that these cultivars may be used as a good natural antioxidant as well as an important basic material of functional foods and biomedicinals.

Key words: grapefruit, phenolics, flavonoid, phenolic acid, antioxidant capacity