The phenolic compounds in different fruit parts including the flavedos, albedos, segment membranes, juice vesicles and seeds of nine grapefruit varieties cultivated in China were determined and their antioxidant capacities were evaluated using three methods. Naringin and neohesperedin were the dominant flavonoids in all grapefruit tested. Fenghongtangmuxun and Jiwei flavedo had the highest contents of naringin (5666.82 μg/g DW) and neohesperedin (1022 μg/g DW), respectively. Gallic acid was the major phenolic acid in all grapefruit tested, and Jiwei juice vesicles had the highest content of gallic acid (343.7 μg/g DW). Fenghongtangmuxun juice vesicles were rich in chlorogenic acid (110.23 μg/g DW), caffeic acid (53.86 μg/g DW) and ferulic acid (23.12 μg/g DW). Overall, the flavedo was rich in flavonoid, while juice vesicle had high amounts of phenolic acid. The Jiwei, Fenghongtangmuxun, Maxu, Huoyan and Hongmaxu grapefruit cultivars contained more phenolics and exhibited higher antioxidant capacities than Shatianyou and Liangpingyou pummelos, and were good sources of natural phytochemical antioxidants.
Keywords: Antioxidant capacity; flavonoid; grapefruit; phenolic acid; pummelo.