| This study was designed to research develop a low-cost Se-enriched yeast product by the use of molasses and urea as fermenting substrate and optimize culture conditions of Se-enriched yeast. At last we used Wistar rats as animal model to evaluate the application effect of the Se-yeast.Trial one was conducted to screen strains with high ability of tolerance to Se and rich in Se, then we optimizated the concentration of molasses and urea in medium. Furthermore we investigated the effects of Se concentration, Se additional time, fermenting time, and Se additional way by single factor test design. The results showed that, under shake flask fermenting conditions with4.5%molasses and4g/L urea in the medium, when15mg/L Se was added at20h post-fermentation, the maximum amounts of biomass and yeast selenium content (10.95g/L and585mg/kg, respectively) were obtained after fermenting60h. In30L fermenting tank, the amounts of biomass and total Se uptake reached17.41g/L and8161μg/L, respectively, when the concentration of Se in medium was24mg/L. The cost of Se-yeast produced in our laboratory was19.6RMB per gram Se, much lower than the commercial Se-yeast.Trial two was conducted to investigate the effects of Se sources and levels on performance, serum biochemical parameters and tissue Se concentration in Wistar rats and quantify the bioavailability value of Se-yeast A produced in our laboratory in comparison with sodium selenite and commercial Se-yeast (Se-yeast B). A total of82female Wistar rats were used in this experiment,6rats were fed the basal diet with0.2mg/kg Se from sodium selenite as depletion control, the others were fed a basal diet without Se supplementation to deplet Se.6Wistar rats from each treatment were slaughtered to evaluate the depletion of Se in rats after two weeks. Then the remaining70rats were allotted to ten treatments with7replicates (1rat per replicate), which were fed a basal diet and the basal diet with0.3mg/kg Se from Se-yeast B or containing Se of0.1,0.2,0.3, or0.40mg/kg diet provided with either Se-yeast A or sodium selenite for21days. The results showed as follows:1) Se sources and levels did not influence on growth performance, serum glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) activities (P>0.05).2) Tissue Se content was increased linearly as the dietary Se level increased (P<0.01), but the increase was markedly higher when Se-yeast A was fed (P<0.05).3) According to slope ratio assay, the bioavailability value of Se-yeast A was95.9%,127.5%,114.5%and101.2%compared with sodium selenite, when serum GSH-Px activity and Se content in liver, kidney and muscle were used as indicators, respectively.4) There were no significant differences on growth performance, serum antioxidant ability in rats between Se-yeast A and Se-yeast B (P>0.05), but rats fed Se-yeast A had more Se retention in kidney and less Se retention in muscle than Se-yeast B (P<0.01). These results indicated that different Se sources had great effects on the deposition of tissue Se, and Se-yeast had higher bioavailability value than sodium selenite, but there were some differences between Se-yeast A and Se-yeast B. Different Se levels had little influence on antioxidant ability, when serum GSH-Px activity was used as indicator,0.1mg/kg Se from Se-yeast or sodium selenite was enough for antioxidant ability, but higher level was required for more Se retention in tissues.It is concluded that,1) Compared with commercial Se-yeast, Se-yeast producted in our laboratory with4.5%molasses and4g/L urea in medium has lower cost,2) Se-yeast from present study not only has higher bioavailability value than sodium selenite, but also has similar bioavailability value with commercial Se-yeast,3) Se sources and levels have little influence on antioxidant ability or growth performance of Wistar rats, but have effect on tissue Se content with higher tissue content at higher level of Se-yeast. |
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