Study On Selenium Enrichment By Yeast And Bioavailability Of Yeast-Se For Rats

This study was designed to explore the production of Se-enriched yeast by yeast,and to determine its bioavailability.Trial one was conducted to study on Se enrichment by yeast.Candida utilis was chosen as the strain for Se enrichment.The effects of different medium,pH value, inoculum,Se additional time and Se concentration on yeast-Se production were studied according to single factorial arrangement.Optimal fermentation conditions were establish-hed by the results above.Optimum medium compositions were yeast extract 1%,peptone 1%,saccharose 5%,original pH 5.1,inoculum 2%.Selenium was added to 15 mg/L in the medium 24 h later since it was fermented on the shake bed with 150 r/min at 28±2℃.The whole fermentation time was 60 h.Under the optimal conditions,the biomass of Se yeast reached 9.7 g/L with the Se content of the cells more than 1300 mg/kg,in which the organic Se is up to 90.9%.Trial two was conducted to study the effects of yeast-Se produced in trial one on growth performance,serum biochemical parameters and tissue selenium retention in Wistar rats.A total of 60 Wistar female rats were allotted by weight into 10 treatments with 6 replicates of 1 rat each.All rats were fed casein-corn-starch Se-deficient purified basal diet for 10 days to delete the endogenous Se in the body,and then were fed diets containing 0.05,0.10,0.15,or 0.20 mg Se/kg diet either from Se yeast or sodium selenite,or fed a basal diet,or diet containing 0.20 mg Se/kg diet commercial Se(Sel-Se) for 10 days.The results showed that,1) There were no significant influences on feed intake(ADFI),daily gain(ADG) and feed gain ration(F/G)(P＞0.05),but yeast-Se seemed to increase ADFI and ADG,and to decrease F/G,compared with sodium selenite;2) Yeast-Se had better effects compared with sodium selenite on increasing serum superoxide dismutase activities(P＜0.05).Addition of Yeast-Se or sodium selenite decreased the contents of serum malondialdehyde(P＞0.05),and increased the activity of serum gluthathione peroxidase(P＜0.01).There was no significant difference between Se yeast and sodium selenite.Serum GPX activities were increased by 22.15%(P＜0.01),23.69%(P＜0.01) and 20.07%(P＜0.01) when 0.20 mg Se/kg was added in the forms of Se yeast,Sel-Se or sodium selenite,compared with the control group.Different Se sources and Se levels had no interactions on serum biochemical parameters(P＞0.05).3) Se sources,Se levels and their interaction had significant influence on serum Se contents(P＜0.01).Selenium concentrations of kidney and liver were increased significantly as dietary Se levels increased.Muscle Se concentrations tended to be increased.There were no interactions on tissue Se contents between Se sources and Se levels.4) According to slope ratio assay, when sodium selenites was used as reference material and activity of GPX,Se concentrations of serum,kidney,and liver as indicators,the relative bioavailabilities of Se from Se yeast were 132.1%,205.7%,140.0%,and 107.2%,respectively.5) The yeast-Se produced in trial one had the similar applied effect compared with Sel-Se.It is concluded that 1) Candida utilis is the optimal yeast.Under the optimal conditions established in this experiment Se content of yeast reaches more than 1300 mg/kg with organic Se up to 90.9%.2) Dietary supplementation of yeast-Se produced in trial one could improve the anti-oxidative capacity in Wistar rats.3) Compared with sodium selenite,yeast-Se had higher bioavailability.