Physicochemical characterization of the fraction components of the theabrownin isolates from Pu'er tea

Abstract

This study focuses on the isolation of theabrownins (TBs) from Pu'er tea. This isolation process involves low temperature water extraction, membrane separation, and multi-stage extraction with organic solvents. Subsequently, purification was performed using column chromatography with macroporous adsorbent resin D-101 and ethanol aqueous solution with a concentration of 0–64.81 g/100g. Five purified fractions were obtained, namely TBs-D1, TBs-D2, TBs-D3, TBs-D4, and TBs-D5, collectively referred to as TBs-D(1–5). These fractions were found to contain TBs and polysaccharides but lacked catechins, caffeine, theaflavin, and free protein. The average molecular weights of these fraction components exceeded 104 Da. These results indicated that TBs-D(1–5) were not free, but combined with tea polysaccharide conjugates (TPC), that is, TBs-TPC complexes. Furthermore, ultraviolet–visible spectrophotometry and Flourier transformation infrared spectroscopy confirmed the nature of TBs-D(1–5) as TBs-TPC complexes. Fluorescence spectra revealed that polysaccharides exert a quenching effect on the intrinsic fluorescence of TBs. Atomic force microscopy indicated that the sample forms a spherical cluster due to the aggregation of theabrownin molecules. Additionally, measurements of interfacial tension and water contact angle demonstrated that TBs-D(1–5) exhibit some amphiphilic properties. This research provides a theoretical foundation for the industrial production and utilization of TBs.