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ABSTRACT: Dried leaves of persimmon, traditionally consumed as a herbal tea in Japan, contain bioactive galloylated flavonol glycosides. Investigation of the seasonal compositional changes in these compounds is important for determining the optimum harvest time. The three objectives were: (1) to elucidate the compositional changes of the flavonol glycosides in persimmon leaves collected in different seasons; (2) to develop an efficient method for separation of the constituents; and (3) to compare their antioxidant activities. Fresh persimmon leaves were collected at different growth stages in 2007 and 2008 in Niigata, Japan. Total flavonols were extracted with 70% aqueous acetone followed by ethyl acetate partitioning, and were analysed by high-performance liquid chromatography. Enzymatic transformation and chromatographic fractionation was performed to isolate the individual flavonols. Two antioxidant assays were performed. Four nongalloylated flavonol glycosides were detected at the leaf-shooting stage, and four additional galloylated flavonol glycosides accumulated during leaf development, resulting in a total of eight constituents. Isolation of nongalloylated and galloylated constituents was successfully achieved through enzymatic transformation of the flavonol mixture using combinations of tannase, β-glucosidase and β-galactosidase, followed by chromatographic fractionation. The gallates were identified as regiospecific 2″-galloylated galactosides and glucosides of kaempferol and quercetin. A mixture of 2″-galloylated flavonol glycosides had a two-fold stronger antioxidant activity than the nongalloylated mixture. This study showed that four 2″-galloylated flavonol glycosides had accumulated in developing leaves of persimmon by the end of May through a rapid 2″-galloylation of the corresponding nongalloylated flavonol glycosides.
Niigata University of Pharmacy and Applied Life SciencesNiahi-niigata, Niigata, Japan