Speciation Preliminary Analysis Of Selenium In Ziyang Selenium-enriched Tea And Extraction Of Selenium-enriched Component

Selenium plays an important role in human metabolic function, we haveknown that there are more than40countries and regions that are short ofselenium in different degrees in the world. Inorganic selenium like sodiumsulfite has a little toxicity in supplementing selenium, generally used inmedicine. It is an important way to supplemente selenium for the crowd lack ofselenium through the food chain, but the selenium content in natural food isgenerally low. Because of that, the development and utilization food rich ofselenium is concerned more and more. Tea is one of the three staple drinks forthe people in the world, the selenium content of Ziyang tea is rich. It is the firstnatural tea rich of selenium passed by scientific appraisal. But literatures haveshown that after brewing Ziyang tea for two times, then water-soluble seleniumwas absorbed was only7%～13%of the total selenium, which can’t meet thehuman’s requirements of selenium.To solve the above problem, the object analyses the selenium form in teapreliminarily, determines the composition with the highest relative content ofselenium, and then optimizes the extraction process of the composition with therich content of selenium, try to provide a theoretical basis for research anddevelopment in natural and safe functional food rich of selenium.Ultraviolet spectrophotometry was used to determine content of seleniumin Ziyang Selenium-enriched Tea with o-diaminobenzene as apparent coloragent under331nm detection wavelength. then studyed o-phenylenediaminedosage, pH and other factors on the results of the analysis. The detectionmethod of selenium in tea was established. By using this method, the minuteselenium content in Ziyang selenium-enriched tea was detected and seleniumdistributed in tea was studied preliminarily.The analytical results showed that the optimal conditions is:2.5mL of 0.2%o-phenylenediamine and2.0mL of5%EDTA in pH=2.0for avoidinglight reaction60min at room temperature. On this condition, there was a goodlinear relationship（R²=0.9989） between absorbance and concentration, theaverage recovery was101.9%and the RSD was2.2%. These results indicatedthat the method was accurate and reliable. The selenium contents in proteins,tea-polysaccharides and tea polyphenol were determined by the methodrespectively. The results indicated that alkali-soluble protein was the majorformat of selenium in Ziyang selenium-enriched tea.In order to optimize extraction condtion of Selenium-protein, according tothe analysis method of center combination test and response surfacemethodology, the effects of NaOH concentration, extraction temperature andratio of solid/liquid on selenium-protein were studied on the basis of the resultsof single factor tests, the regression model of the extraction effect ofselenium-protein. In order to study the process conditions of ultrasound-assistedextraction of the selenium protein in tea, on the basis of the single-factor test,orthogonal test was designed, which had four factors that were the ultrasonicpower, extraction temperature, solid-liquid ratio and alkali concentration, andevery factors had three levels. Then we obtained the optimumultrasonic-assisted extraction conditions. The results showed that:（1） Alkali optimal parameters were: alkali concentration was0.09mol/L,the extraction temperature was67℃, the ratio of solid to liquid was55:1（g:mL）, each time extracted for3h, then we extracted two times. Selenium-proteinextraction rate was56.52%and the selenium content was4.89μg·g^-1, which wasaccounting for41.0%of the tea total selenium content.（2） The optimal parameters of ultrasound-assisted extraction:0.12mol/LNaOH, the liquid-solid ratio was1:70, and ultrasonic power was100W,then itwas extracted for50min at70℃for two times. On this basis, selenium proteinextract rate was71.87%, the selenium content was5.09μg·g^-1, which wasaccounting for46.67%of the tea total selenium content.