Preparation And Characterization Of Selenoproteins From Selenium-enriched Yeast

Selenium is a necessary trace element for human body,which has important physiological functions.While inorganic selenium has a certain toxicity on the human body,which can be transformed into proteins and polysaccharides of cell,through these processes,inorganic selenium becomes an organic form.With high biological activity and low toxicity,selenoproteins are considered to be the first choice source of selenium for consumers.In this thesis,we chose yeast as a carrier.The optimal medium composition and optimal fermentation conditions of selenium-enriched yeast,selenoproteins extraction and selenium content of selenoproteins,structures and functional characterizations of selenoproteins were studied.This study would provide important evidences for further research of selenium-enriched yeast and selenoproteins.The main contents were as follows.Through single factor and orthogonal experiments to determine the optimal medium composition,the optimal medium:glucose 30.00 g/L,beef extract 7.00 g/L,urea 8.00 g/L,25.00 ?g sodium selenite/mL broth,yeast extract 6.00 g/L,KH2PO4 6.00 g/L.Through single factor and response surface experiments,the optimal fermentation conditions:27 ?,pH 5.6,6 h,added 7.50?g sodium selenite per mL broth,added 17.50 ?g sodium selenite per mL broth,ample volume 50 mL/250 mL,shaker revolutions 200 r/min,fermentation time 35 h,inoculum 6%.Selenium-enriched yeast biomass was 8.15 g/L,the total selenium content of selenium-enriched yeast was 3430.74 ?g/L.The selenium content of selenoproteins was 1013.15 ?g/g.Compared to yeast proteins,selenoproteins showed a better ability of hydroxyl radical scavenging and certain DPPH·free radical scavenging,it also showed better reducing power than yeast proteins.From the polyacrylamide gel electrophoresis analysis,the bands of selenoproteins were found consistent with yeast proteins.FTIR analysis showed there was little difference between proteins and selenoproteins.Selenoproteins in 1077 cm-1 and 526 cm-1 had strong absorption peaks,which were H-Se bond vibrations,Se=O bond structure.SEM analysis showed that selenoproteins showed chunks of flaky,while yeast proteins showed smaller sheets.These may cause a difference in the physical properties of the selenoproteins.