Abstract:

Hesperidin is one of the flavonoids existing in citrus fruit peel or physiologically fallen fruit before maturity, especially in the latter with over 3% content. Synephrine, an alkaloid, is mainly contained in immature citrus fruit as well, and the more mature the fruit becomes, the lower its content is. The physiologically fallen fruits of 7 citrus species were collected at two periods of pre-harvest fruit drop and dried by an up-draught drying fan or in natural air. These samples were analyzed for their hesperidin and synephrine contents by HPLC. The hesperidin analysis was carried out on a Hypercil ODS2 column (250 mm × 4.6 mm，5 μm) using a mobile phase composed of water, acetonitrile, THF and acetic acid (80:16:3:1, V/V) with UV detection set at 280 nm; the mobile phase (containing 0.2 g SDS/100 ml) for analyzing synephrine was an acetonitrile-water-phosphoric acid (32:68:0.2, V/V) system, and the detection wavelength was set at 225 nm. The results indicated that the contents of hesperidin in all the citrus species treated with 80 ℃ hot air were higher than those treated by natural air, 40 ℃ hot air, or 60 ℃ hot air. The contents of synephrine in all citrus species treated by 60 ℃ hot air were higher than those with other treatments. Moreover, the contents of hesperidin and synephrine were different greatly among different citrus species and between the periods of preharvest fruit drop. The hesperidin content in citrus fruits at the second period of physiologic drop was higher than that at the first period except for Guanxi honey pomelo and sour orange. The highest content of hesperidin was observed in Guanxi honey pomelo at the first period, reaching (199.28 ±0.7)μg/mg. While the synephrine content in the fallen fruits of all the citrus species at the first period were higher than that at the second period, especially satsuma mandarin fruit (Citrus unshiu Marcovitch, cv. Owari) had the maximum synephrine content of (20.50 ±0.89)μg/mg among all the species.

Key words: citrus, physiological fallen fruit, hesperidin, synephrine, HPLC