The flavonoid, carotenoid and pectin content in peels of citrus cultivated in Taiwan

The flavonoid, carotenoid and pectin composition in peels of eight varieties of citrus {Ponkan (Citrus reticulata Blanco), Tonkan (C. tankan Hayata), Murcott (C. reticulate × C. sinensis), Wendun (C. grandis Osbeck), Peiyou (C. grandis Osbeck CV), Kumquat (C. microcarpa), Liucheng [C. sinensis (L.) Osbeck], and Lemon [C. limon (L.) Bur]} cultivated in Taiwan was determined. The total flavonoid content exceeded the total carotenoid content. Ponkan (C. reticulata Blanco) peel had the highest total carotenoid content (2.04 ± 0.036 mg/g db) and Wendun (C. grandis Osbeck) and Peiyou (C. grandis Osbeck CV) peels, the lowest (0.036 ± 0.0006 and 0.021 ± 0.0004 mg/g db, respectively). Naringin was abundant in Peiyou (C. grandis Osbeck CV) and Wendun (C. grandis Osbeck) peels (29.8 ± 0.20 and 23.9 ± 0.32 mg/g db, respectively) and hesperidin was aboundant in Ponkan (C. reticulata Blanco), Tonkan (C. tankan Hayata), and Liucheng [C. sinensis (L.) Osbeck] peels (29.5 ± 0.32, 23.4 ± 0.25, 20.7 ± 0.38 mg/g db, respectively). Kumquat (C. microcarpa) peel contained the most diosmin (1.12 ± 0.03 mg/g db) and quercetin (0.78 ± 0.003 mg/g db). Levels of caffeic acid (3.06 ± 0.03–80.8 ± 3.72 μg/g db) were much lower than that of chlorgenic acid, ferulic acid, sinapic acid and ρ-coumaric acid. Ponkan (C. reticulata Blanco), Kumquat (C. microcarpa) and Liucheng [C. sinensis (L.) Osbeck] peels contained the most total amounts of lutein, zeaxanthin, β-cryptoxanthin, and β-carotene (114, 113, and 108 mg/g db, respectively). The total pectin content ranged from 36.0 ± 1.46 to 86.4 ± 3.36 mg/g db.