Studies On Structure, Conformation And Bioactivities Of Polysaccharides From Green Tea

Much attention has been focused on natural polysaccharides because of its multiple bioactivities, pharmacological activities and safety. The conformation of polysaccharides has stronger effects on bioactivities according to the recent studies. Tea, which is the most popular beverage in the world, was studied in this paper. Tea polysaccharides (TPS) fractions were isolated and purified from low-grade green tea. And the physico-chemical properties and the chemical structure of TPS fractions were investigated. The solution behavior and three-dimensional conformation of tea polysaccharides fraction (TPS4-1) were also investigated here, with the advanced methods of isolation and purification technique, chemical and instrument analysis technique of biomacromolecular. The correlation between bioactivities and the conformation of polysaccharides was discussed. The main results indicated as follows:Extraction of bioactivity components in tea leavesThe affinities of polysaccharides, polyphynols and purine for the medium were different because of their differential structures. So a new technique that could isolate tea polysaccharides, tea polyphynols and caffeine from the same tea continuously was obtained based on that. Fifteen kinds of resins were compared on the capability of static, dynamic adsorption and desorption to tea polyphynols and caffeine. And the yield of tea polysaccharides, tea polyphynols and caffeine were 1.0%, 4.9% and 1.7%, respectively.Purification and chemical structure of tea polysaccharidesTPS4-1, which was a relative homogeneous fraction, was obtained by the various chromatography techniques of absorbent chromatography, ion exchange chromatography and sephadex chromatography. It was found that TPS4-1 was a polysaccharide-protein- nucleic acid conjugate by using the methods of UV, IR, NMR, HLPC, GC, gelose electrophoresis, periodate oxidation, smith degradation. The results showed that the molecular average-weight of TPS4-1 was 12.0 104, and the content of uronic acid, protein and neutral sugar were 54.4%, 3.7% and 38.1% respectively. TPS4-1 was composed of Ara, Rib, Xyl, Glc and Gal with a molar ratio of 4.88:2.19:3.07:1.82:1.00. The results of P -elimination reaction indicated that the chain of polysaccharides and protein was connected by O-Iinked chemical bond. The backbone of sugar residues chain in TPS4-1 were connected mainly by 1-4 and 1 -6 , and TPS4-1 contained a and type glycosidic linkages. The residues amount of monosaccharide, uronic acid and amino acid in one molecule of TPS4-1 were 295, 334 and 36 respectively.Solution behavior and conformation of tea polysaccharidesBy using the technique of AFM, CD, LS and UV, the three-dimensional conformation and solutionbehavior were studied. Results showed that the molecule of TPS4-1 twisted each other, which formed random coils and islands large or small. The molecular chain parameter was 100-500nm in length, 20-40nm in width and 0.5-2.6nm in thickness. The intrinsic viscosity [ 1 ] - molecular weight relation (Mark-Houwink eaquation) for the tea polysaccharides in 0.2M NaCl solution was found to be represented approximately by [ 1 ] = 0.0416 Mw049 cm3 g"' , which had the hemi-flexible and high branch chain, with the technique of LS, Vis, Congo-red reaction and I2-KI reaction etc. The conformation could be changed by the factors of pH, temperature, ion intensity etc. The results of SEM, X-ray and DSC indicated that the state structure of tea polysaccharides was noncrystal, and the vitrification temperature was 62 .Antioxidant effects of tea polysaccharidesThe aritioxidant effects of tea polysaccharides from different sources in vitro were studied in this paper. Tea polysaccharides have inhibiting effects on hydroxyl radical (OH) and superoxide anion radical (CV). And have the inhibiting effects on lipid peroxidation with mice liver in vitro. It also could protect liver from peroxidation induced by Fe2++H2O2, inhibit the mitochondria swelling and hemolysis of red blood cells. The antioxidant effects of tea polysacc...