Preliminary Studies On The Preparation Of Thearubigin Fractions And Their Free Radical Scavenging Activities

Thearubigins are heterogeneous acidic phenolic pigments in black tea,which are mainly flavanol polymers with a molecular weight distribution of 700-40000 and contribute to the color and taste of black tea.Because of their heterogeneity, thearubigins are difficult to be purified from black tea,which lead to the limited information on their structure,composition and characteristics.By far,there are a few reports on their preparation,which only focused on the solvent extraction and chromatographic separation.In the past sixty years,thearubigins have intrigued many research groups to explore,but there still have no breakthrough on their characteristic.In this paper,five thearubigin fractions named after PBP-1 to PBP-5 were prepared from Keemun black tea with solvent extraction and ethyl ether precipitation. All of them were free of catechins,theaflavins and caffeine by the analysis of HPLC. In the reducing power tests,the five thearubigin fractions at the concentration of 13.2-150μg/ml had been shown to have a reducing power in a dose-dependent manner.With the polarity increase of thearubigin fractions,the reducing power was tend to decrease.In the Fenton system,the scavenging activities of five thearubigin fractions to hydroxyl radicals were raised with the increase of their concentration from 13.2μg/ml to 150μg/ml.With the polarity increase of thearubigin fractions, their scavenging capacity was decreased.In the pyrogallol autooxidation system, five fractions at the concentration of 13.2-150μg/ml had a slight inhibition of the formation of superoxide anion with the maximal inhibition as 48.22%.The inhibition percentage was mainly ranged from 10%to 25%.In the DPPH system,all of fractions at 13.2-100μg/ml executed scavenging activities in a dose-response way as similar as the performance in the Fenton system.Moreover,their scavenging activities to DPPH radicals were decreased with the increase of the polarity.Those results have shown that thearubigins as like as their major precursors-catechins and theaflavins are capable to eliminate free radicals,which mainly due to the contribution of the residue of the active phenolic hydroxyl groups and benzotropolone groups at the thearubigin molecule.Thearubigins-the most abundant polyphenolic substances in black tea may have a potential to execute biological effects after tea drinking.