Determination of flavone C-glycosides in tea

Abstract

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.

Major flavonoids in dry tea

“…Neither of these studies detected flavones for three possible reasons: co-elution of the flavones with flavonols, hydrolysis may have destroyed some of the flavone aglycones or not hydrolyzed the C-glycosides of flavones, and what little was present was below the limit of detection. The third study (Engelhardt et al, 1993), which measured the presence of flavone glycosides, was specific and thorough. There were 39 flavone datapoints, 32 for black (80%), four for green (10%), two for oolong (5%), and two for Pu'er teas (5%).…”

The analysis by HPLC of green, black and Pu'er teas produced in Yunnan

“…Engelhardt et al (1992) have reported that the profile of FG may be characteristic of the variety of fresh leaf used in tea manufacture. They examined only two teas from China, one in which quercetin derivatives dominated Traces of theaflavins were found in the Quingmao tea but were not detected in the steamed tea suggesting that there had been some PPO activity prior to firing but that such activity had been inhibited by the steaming process.…”

Analysis of Green Tea Compounds and Their Stability in Dentifrices of Different pH Levels

“…10,11) In addition, phenolic acids (chlorogenic acid, gallic acid, and caffeic acid) and purine alkaloids (caffeine, theobromine, and theophylline) are contained in green tea. 10) Green tea is one of the beneficial herbal ingredients for dental health.…”