Bioflavonoid Profile of Exotic Citrus Species

The levels of the flavanones naringin, hesperidin, narirutin, eriocitrin, neohesperidin and neoeriocitrin, and the flavone diosmin were evaluated in fruits of several exotic citrus (citron, pummelo, sour orange, papeda, mandarin and lemon). The highest total flavonoid content was detected in sour oranges and mandarins, while low to non-detectable levels were found in pummelo, papeda, citron, and lemon cultivars. Average total bioflavonoid values on a dry weight basis were between 4-5 % in both sour oranges and mandarins. Individual flavonoids varied among species. Naringin, neohesperidin, and neoeriocitrin were found in some sour orange cultivars. Hesperidin was the only flavonoid detected in mandarin. Pummelos showed a diverse flavonoid profile. Some pummelo varieties had up to 6 different flavonoids (narirutin, naringin, hesperidin, eriocitrin, neohesperidin, neoeriocitrin). Citrus flavonoids have a wide variety of clinical applications. This information should prove useful to the nutraceutical industry in identifying alternative sources of flavonoids. INTRODUCTION Citrus fruits have been widely recognized for their medicinal applications such as antioxidant, anti-inflammatory, cholesterol-lowering, anticancer, and antiviral among others (Benavente-Garcia, et al., 1997). Flavonoids are key phytochemicals supporting citrus medicinal properties and contributing to the sensory quality of these fruit (Garg et al., 2001; Kris-Etherton et al., 2002; Middleton et al., 2000; Peterson and Dwyer, 1998; Ren et al., 2003; Silalahi, 2002; Tomás-Barberán and Clifford, 2000). Furthermore, they are also important in chemotaxonomy as each species of Citrus is characterized by a particular flavanone glycoside pattern (Berhow et al., 1996; Rouseff et al., 1987). Flavanones such as eriocitrin, narirutin, hesperidin, naringin, and neohesperidin are characteristic of common citrus fruits (Tomás-Barberán and Clifford, 2000) and have their health benefits known as referenced above. Minor flavonoids such as flavones also play an important nutraceutical role (Marín and Del Río, 2001). The main location on the fruit for these flavonoids is on the peel (Tomás-Barberán and Clifford, 2000). It is desired to find new citrus sources that can provide a broad spectrum and/or a high concentration of flavonoids. For this communication, we have analyzed 12 exotic citrus species and/or cultivars to investigate their potential application in dietary supplements and functional foods based on the total flavonoids content and profile. Proc. XXVI IHC – Future for Medicinal and Aromatic Plants Eds. L.E. Craker et al. Acta Hort. 629, ISHS 2004 Publication supported by Can. Int. Dev. Agency (CIDA) 450 MATERIALS AND METHODS Plant Material In most cases, species were selected based on their peel thickness; others were selected based on previous knowledge of their being rich sources of the bioflavonoids of interest (Pusateri, 1998). Samples of each fruit group were harvested at an immature stage in December 2000 from the USDA-ARS Citrus National Clonal Germplasm Repository/ UC Riverside Citrus Variety Collection (Riverside, CA). Table 1 notes the genus species, cultivars, groups and study names of the species tested. Samples were freeze dried and milled into powder using a Universal Mill (Bauermeister, Inc, Memphis, TN) with a 1.5 mm screen. Flavonoids Analysis Seven different flavonoids were evaluated including 6 flavanones (naringin (N), hesperidin (H), narirutin (NR), eriocitrin (E), neohesperidin (NeoH) and neoeriocitrin (NeoE)), and one flavone (diosmin (D)). Samples were prepared by dissolving 0.25 g of freeze dried powder in 25 ml of extraction solvent (methanol: DMSO 4:1), sonicated at room temperature for 30 min. Liquid sample was filtered through a 0.45 μm filter into an HPLC autosampler vial. The linear range for standard calibration was 5–500 ppm. The HPLC system consisted of a Hewlett Packard HPLC 1100 (Palo Alto, CA) with a dual absorbance detector (DAD) and a Waters C18 symmetry column (250 x 4.6 mm i.d.) at ambient temperature. Flow rate was 1.0 mL/ min, injection volume 10 μl, detection wavelength 280 nm. A gradient mobile phase was used (Table 2.). Sugar Analysis A Perkin-Elmer HPLC system (Wellesley, MA) equipped with a refractive index detector, an amino propyl column (250 x 4.6 mm i.d.) (Altech, Deerfield, IL) with thermostat at 25 C was used. Mobile phase was isocratic with a mixture of 70 % acetonitrile and 30 % water and flow rate was 1 mL/min. RESULTS The total flavonoids identified in this study are presented in Figure 1. Species with the highest total flavonoids (% w/w) were sour orange ‘myrtifolia’ with 5 % and sour orange cv. ‘Gadadehi’ and mandarin hybrid cv. ‘Nova’ both with 4.6 % each. Pummelo hybrids followed with 2.6 %, 2.4 % ad 1.9 % for cvs. ‘Pong Yau’, ‘Yuma Ponderosa’, and ‘Tresca’, respectively. Papeda Hybrid cv. ‘Ichang Lemon’ and papeda cv. ‘Honghe’ had 2.4 % and 1.8 %, respectively. Citron species were 1.5 %, 0.6 % and 0.5 % for cvs. ‘Bengal’, ‘Odorata’, and ‘Diamante’, respectively. Last, Lemon Hybrid cv. ‘Ponderosa’ registered 0.7 %. The breakdown of individual bioflavonoids is noted on Table 2. Pummelo Hybrid cv. ‘Yuma Ponderosa’ had the broadest variety of flavonoids with a total of 6 (1.4 % NeoH, 0.6 % NeoE, 0.2 % N, 0.1 % H, and 0.04 % each for E and NR). Sour orange ‘myrtifolia’ contained 3 flavonoids (2 % NeoH, 1.6 % NeoE, and 1.5 % N). Species containing 2 flavonoids were citron cv. ‘Bengal’ (1.2 % NeoH and 0.3 % N); papeda cv. ‘Honghe’ (1.6 % N and 0.2 % E); pummelo cv. ‘Tresca’ (1.2 % N and 0.7 % NR); citron cv. ‘Diamante’ (0.3 % H and 0.2 % D); and citron cv. ‘Odorata’ (0.4% H and 0.3 % D). Single flavonoid species were: sour orange cv. ‘Gadadehi’ (4. 6% N), mandarin hybrid cv. ‘Nova’ (4.6 % H) and lemon hybrid cv. ‘Ponderosa’ 0.7 % NH. Total sugar content is displayed in Figure 2. Values were as low as 22 % for both papeda hybrid cv. ‘Ichang Lemon’ and pummelo hybrid cv. ‘Yuma Ponderosa’ and as high as 46 % for citron cv. ‘Odorata’. With the exception of mandarin hybrid cv. ‘Nova’, glucose and fructose were the dominant sugars in immature fruit (Table 3).