Mutagenic Screening And Culture Condition Analysis Of Selenium-riched Yeast

Selenium-enriched yeast is a widely used food additive and an important organic selenium supplement for the human body.It is derived from yeast cells that convert inorganic selenium into organic selenium during the growth process.The yeast strain with the high potential of converting inorganic selenium into organic selenium is of great significance to the production and application of selenium-enriched yeast.Selenoprotein is a major form of organic selenium in selenium-enriched yeast.Its content is not only an important indicator of the quality of selenium-enriched yeast,but also reflects the ability of yeast to convert inorganic selenium into organic selenium.Studies have shown that monoselenophosphate is a donor of activated selenium for selenoprotein synthesis and is catalyzed by selenophosphate synthetase?SPS?,which is the rate-limiting enzyme for selenoprotein synthesis.In view of the intolerance of SPS activity to H₂O₂,the present study first used H₂O₂as the selection pressure to screen the selenium-enriched yeast strains,and then analyze the culture condition for the selenium-enriched yeast strains to enrich organic selenium.The main research results obtained are as follows:?1?Two strains?HXS-01 and HXS-02?with a high of enriching organic selenium were isolated from a normal Saccharomyces cerevisiae strain as the starting material through treatment of Na N₃as mutagen and isolation of H₂O₂as selection pressure.After shaking flask fermentation for 48 h,the content and yield of total selenium and the content and yield of organic selenium in HXS-01 and HXS-02were 3.4-3.7 times,2.9-3.2 times,3.7-4.0 times and 3.1-3.5 times higher than in the starting strain,respectively.The potential of HXS-02 for enriching organic selenium was better than that of HXS-01.The total selenium content and yield of HXS-02 with a more than 97%percentage of organic selenium in total selenium were2 303.97?g/g and 7 945.19?g/L,respectively.?2?Selenium-enriched yeast strains not only had a stable capacity of highly enriching organic selenium,but also expressed high SPS activity and high selenoprotein content.The total selenium content,organic selenium content,total selenium yield,and organic selenium yield of the strains HXS-01 and HXS-02after 6 consecutive subculture were 3.9-5.2 times of the starting strain.Their SPS activity and selenoprotein content were 1.7-2.1 times and 1.9-2.1 times that of the starting strain,respectively.?3?The culture conditions for enriching organic selenium of selenium-enriched yeast strains were preliminarily determined.Under the conditions of incubation temperature of 28?,rotation speed of 180 r/min,inoculation volume of 10%and loading volume of 50 m L/250 m L,the optimal addition time and concentration of sodium selenite were 8 h and 62.5?g/m L,and the optimal selenium-enriched incubation time is 24 h.Fructose,reduced glutathione and reduced coenzyme?could effectively increased the total selenium content,total selenium yield,organic selenium content and organic selenium yield of strain HXS-02,and their suitable concentrations were 6 g/L,26 mmo L/L and 0.20 mmo L/L,respectively.In summary,the selenium-enriched yeast strains could be effectively screened using H₂O₂as the selection pressure,and the obtained selenium-enriched strains could convert inorganic selenium into organic selenium at a high level under suitable culture conditions.SPS activity analysis and selenoprotein content determination showed that the H₂O₂-resistant strains had high SPS activity,which might contribute the strains with high ability to enrich and convert inorganic selenium to organic selenium.