Determination of flavone C-glycosides in tea.

An HPLC method for the determination of flavone C-glycosides (FCG) from black tea has been developed. Sample clean-up was accomplished by means of polyamide column chromatography, followed by enzyme hydrolysis of interfering compounds such was flavonol glycosides and a second polyamide column chromatographic step. Using HPLC with gradient elution and photodiode array detection eight FCG were separated. Seven FCG were isolated by means of preparative HPLC. Identification was carried out using co-chromatography, FAB(Fast Atom Bombardment)-mass spectrometry and various nuclear magnetic resonance techniques. Apigenin 6-C-glucosyl-8-arabinoside (schaftoside) and apigenin 6-C-arabinosyl-8-C-glucoside (isoschaftoside) as well as luteolin 8-C-glucoside (orientin) and luteolin 6-C-glucoside (isoorientin) have been detected in tea for the first time. Three of the other compounds have been identified as apigenin 8-C-glucoside (vitexin), apigenin 6-C-glucoside (isovitexin) and apigenin 6,8-di-C-glucoside (vicenin-2). Their occurrence in tea has been previously reported. From its UV spectrum another compound was concluded to be an apigenin glycoside. The FCG were quantified in a variety of teas of different origins (16 black, two green and one oolong). The total amounts of the FCG were 0.48-2.69 g/kg dry weight. The FCG pattern of teas of different origins were similar to each other and no origin-dependent characteristics have yet been observed. Small amounts of FCG (1.2-2.2 mg/kg) were detected in hydrolysates of high relative molecular mass fractions (Mr > 5000) of a black tea liquor.