Study On Chemical Speciation Of Selenium And Polysaccharides Of Selenium-riched Tea

In this paper, se-riched tea leaves produced in Enshi were taken as raw material,constituents of which were determinated and chemical speciation of selenium inwhich was investigated. In addition, tea polysaccharides containing selenium weresuccessively extracted, seperated and purified. Composition and bioactivity of themwere also studied. The main contents of this paper were the following parts:1)Hydride generation atomic fluorescence spectrometer for the determination ofselenium in instrument conditions was optimized. The results showed that whenselenium lamp current is35mA, negative high voltage is290V，1%sodiumborohydride reducing agent, reaction media20%, carrier fluid3%, the precision andaccuracy of the methods meet requirements, recovery ranged from95to100%，andthe detection limit reached0.21^ig/L. Under optional conditions, selenium contentsof cropper grown in se base were successively determinated, results showed mostcrops contained high amounts of selenium, indicating the regional characteristics ofselenium. After comparing selenium content of the tea leaves and their correspondingsoil，we found total selenium content of the soil did not have a correlation of that oftea, but content of effective state of selenium in soil showed a good positivecorrelation.2)The contents of several different nutrients containing polyphenols,polysaccharides and flavonoids and so on in se-riched tea were measured. In addition,four harmful elements (Hg, Pb，As, Cd) were also determinated. It was found thatthere were no significant differences in nutritional content of differnt kinds of tea,however, in the low mass fraction, w (Se) with w (As) in showed a reverse trend,which implied Se had an antagonistic effect on arsenic. And w (Se) with w (Pb) is notdirectly related, the other two elements mercury and cadmium were below thedetection limit of the instrument and were not detected. Of enriched tea the crudepolyphenols, polysaccharides, soluble protein, alkali-soluble protein and tea grounds were extracted, and the yields, purity and selenium content of them were analyzed.The results shows selenium is mainly concentrated in the tea grounds (75.4%),further is concentrated in protein, followed by polysaccharides and crude polyphenol,indicating that we can only get small parts of the selenium through the tea waterextract.3)Crude tea polysaccharide were extracted using boiling water, and four kinds ofsecondary components were separated and puriifed by a series of steps. Of whichSe-TPS2had the highest rate (37.14%)，and both Se-TPSl and Se-TPS2wereidentified relatively homogeneous component by liquid chromatography HPGPC,molecular weight (Mw) were106kD and244kD. Concentration of uronic acid ofthree purified polysaccharides were47.25%，69.98%，62.16%respectively. All ofthem contained a small amount of protein, which indicated the acidic polysaccharidesobtained were glycoprotein. Monosaccharide compositions were measured by ionchromatography as the following.fucose，rhamnose，arabinose，galactose，glucose，glucuronic acid and galacturonic acid, and the molar ratio is0.07:0.21:0.58:1:0.47:0.17:1.75,0.07:0.28:0.59:1:0.10:0.49:1.24and0.07:0.38:0.72:丨:0.30:0.19:0.88respectively. The selenium amounts of purified polysaccharides (0.97mg/kg,0.44mg/kg，0.34mg/kg) significantly reduced compared with coarse polysaccharides,indicating polysaccharide contained other substances in combination with selenium.In additoin，elemental analyzer, ICP and other instrumentations were applied forelemental detection of selenium polysaccharide. Activity inhibitory experimentsshowed polysaccharides of selenium-enriched tea had inhibitory effect on twoenzymes, tea polysaccharide Se-TPS for a-glucosidase activity inhibition rate was75.1%, Se-TPS2enzyme inhibition rate of were above50%. Tumor inhibition rate ofenriched tea polysaccharide in mice were50%, which were considerable to thepositive control cyclophosphamide. At the same time, selenium polysaccharide cansignificantly improve the thymus index and spleen index.4)The spectral information, the apparent shape and thermal properties ofselenium polysaccharide were analyzed. Polysaccharide Se-TPS was found a clearpeak in the protein signal range250?300nm. Purified polysaccharide decreased significantly at this absorption peak, and no signal peak was found in Se-TPS2withinthis range absorption peaks. IR spectra of them were basically indistinguishable onlywith some differences in the intensity of bands. The absorption bands within the rangeof1000?1200cm’1,2800?3200cm’1and3200?3600cm1were the characteristicabsorption peaks of polysaccharides. And the COOH-and C=0functional groupshave appeared, directly illustrated the polysaccharides were acidic sugar. TGAanalyzer found weightlessness trends of polysaccharide under the heating conditions(0?500oC) are similar. In the range of200?280。C, severe oxidative decompositionreaction occured. Apparent morphology of polysaccharide was observed by scanningelectron microscopy (SEM). Maybe due to its soft and amorphous state, the purifiedpolysaccharide was easy to form a variety of irregular huddled shapes.5) Analysis by partial acid hydrolysis, two polysaccharides fucose and mannoseonly present in the retentate, indicating they may be branched component parts ofSe-TPS2. Xylose hydrolysis only at high concentrations of acid, showed it may beexist in the position difficult to hydrolysis of the branched chain. And GalA was neverdetected in solution by hydrolysis, indicating that it only exist in the main chain.Periodate oxidation and smith degradation experiment showed, the initial determinedchaining glycoside bond may be1—6bit or bit1—，there also may be a large amountof1—2，1—2,6，1—4,1—4，6or furanor1—glycosidic bond. And concrete structuresneed to be further explored.