| The Qinghai-Tibet Plateau, which includes Tibet, Qinghai, west Sichuan, southern Xinjiang, has an average height of 4,000 ~ 5,000 m, and occupies 26% of Chinese area. Selenic deficiency is widely spread in Tibetan Plateau due to its unique geological structure, grass types, alpine climate and other environmental factors. Selenium deficiency not only has relations with Beck disease and Keshan disease in human, it also leads to a generally high incidence of selenium deficiency diseases such as white muscle, slow growth, diarrhea in Tibetan sheep and yaks. As studies have shown, selenium supplement can improve the growth performance of those animals raised in regions of selenium deficiency. The Feed Additives Directory(2013) from ministry of agriculture suggests that selenium can be supplied and replenished in sodium selenite or selenium yeast. Selenium-enriched yeast can not only provides element Se, but also provides protein, carbohydrates and vitamins, which is also of a high bioavailability.The purpose of this project is to screen a strain of yeast with enriched selenium capacity, which isolated from the yak traditional fermented yogurt. And then treat it as a carrier and further develop it. The project eventually provides food-grade selenium supplement for prevention and control of selenic deficiency in the Qinghai-Tibet Plateau. Results of this test are as follows:1 Successfully developed a high selenium content of selenium-enriched yeastIn order to screen a good capabilitity of selenium-enriched yeast, two strains of saccharomyces cerevisiae?one strain of pichia pastori and kluyveromyces marxianus were isolated from yak yogurt have been utilized in this experiment. Selenium-resistant abilities are compared by the means of applying seed hydraulic(1×105CFU/m L) on selenium-resistant plates of different concentrations( 0,5,10... 90?g/m L), and the result shows that the Se-resisting concentration of saccharomyces cerevisiae SWUN5668 and SWUN5696 is 20 ?g/m L, pichia pastori SWUN5680 and kluyveromyces marxianus SWUN 5666 are 15?g/m L.To determine the Se-enriched ability of four strains, viable count, the biomass and content of selenium were compared by adding yeast(1×107CFU/mL)to 60 mL YEPD fermentation broth(the level of selenium is 15?g/m L)and cultivating 36 h. The result shows that viable count(6.5×107CFU/m L) and biomass(0.1400g) of saccharomyces cerevisiae SWUN5668 are the highest, and its Se content is 35.84?g. Therefore, by screening two trials, yeast SWUN5668 has been determined as a carrier regarding the development of enriched selenium capacity. The growth curve was determined by OD value method and the viable plate count method, the results indicated that adaptation of this strain is 0-4h, the logarithmic phase is 4-10 h, the plateau is 10-68 h, the decline phase is 68-72 h, the viable count reached a maximum of about 1.05×108CFU/m L at the 24 th hour. The optimum conditions were gained by measuring the time for cultivation and different selenium concentrations, which is to add 15?g/m L sodium selenite to YEPD fermentation broth which has cultivated for 10 h and continued to cultivat 36 h, viable cell number and biomass were respectively 8.35 × 107CFU/m L and 3.2g/ L. the selenium content of selenium-enriched yeast is 1553?g/g with the national standard method. Therefore, this test successfully developed a selenium-enriched yeast, providing an effective material for selenium supplement for human and animals in Tibet plateau.2 The effects of Selenium yeast on growth of ratsIn order to evaluate the effects of Selenium yeast on animals, 21-day-old healthy level male Wistar rats were experimented as test animals, which were divided into 7 groups(N=18). Group 1 was the blank group(Only fed the basal diet, selenium content <0.027mg/kg); Group 2-4 were the control groups(Fed with yeast vector corresponding to the total.); Group 5-7 were the treatment groups(Fed with different doses of selenium yeast basal diet, selenium contents were respectively 0.05mg/kg, 0.2 mg/kg and 0.5 mg/kg), all groups were fed for 8 weeks. from the start of the experiment, the rats were weighted at intervals of one week. In order to evaluate the performance of selenium enriched yeast on the growth, intestinal development, reproductive system development and tissue deposition level of selenium in rats, six rats were randomly selected in each group at the 4th, 6th, 8th weeks for heart blood sampling, intestines, organs and muscle sampling.Results showed that the average daily gain of groups fed with selenium concentrations of 0.05 and 0.2 mg/kg is significantly higher than that of the blank group and the control group(P<0.05). Daily gain of the 0.5 mg/kg group increased compared with the control group, but the effect was not significant. Daily gain of the 0.5 mg/kg group compared with the blank group increased significantly(P<0.01). The selenium groups can promote the development of small intestine villi, they had the best effects on the duodenum, the jejunum secondly and little effect on the ileum. High concentrations of selenium(0.5mg/kg) at the 8th week can significantly increase the sperm number of seminiferous tube cavity and it had little effect on the growth of the epididymis. Fed with selenium concentration of 0.2mg/kg and 0.5mg/kg group can significantly increase the selenium content of liver and blood in rats at the 4th week and the 8th week(P<0.05).Selenium content of muscle increased significantly at the 8th week with the increase of selenium concentration(P <0.05). Selenium's effects on serum testosterone and testicular glutathione peroxidase had no significant difference. 0.2 mg/kg and 0.5 mg/kg selenium levels can significantly increase the hepatic glutathione peroxidase at the 8th week, and 0.2 mg/kg selenium level can significantly increase the serum glutathione peroxidase at the 8th week(P<0.05). Therefore, the selenium-enriched yeast developed by this test can increase daily gain of rats, promote intestinal development and increase the selenium content of edible parts. |
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