Preparation Of Selenium-enriched Candida Utilis And Its Biochemical Capacities In Rats

Selenium (Se), an essential nutritional trace element, is required in a variety ofmetabolic functions and numerous health effects. However, its absence in the body ofhuman and animals can lead to many diseases. Supplementation of Se in diet in theform of organic or inorganic Se can prevent Se deficiency. Inorganic selenium is notwildly used because of its greater toxicity. Supplementation with selenized yeast is themost popular approach to prevent Se deficiency because it has high protein andvitamine B content, high security and bioavailability. Meanwhile, selenized yeast can beused to protect cells against damages caused by free radicals, improve the immuneperformance.Preparation of selenium yeast is usually carried out by adding a certainconcentration of inorganic Se source material to the medium during the process of yeastculture, and selenium-enriched products are obtained along with the growth andmetabolism of yeast cells. Candida utilis, a kind of industrial yeast, is now used for thepreparation of selenium-enriched yeast, because it can accumulate high concentrationsof inorganic Se and glutathione (GSH) intracellularly. Se-enriched C. utilis with highperformance (high organic Se content and high GSH content) will have a wider marketand application prospects owing to its improving the immune system.GSH, an important intracellular antioxidant, plays a key role on protecting cellsagainst damages caused by free radicals and toxic substances. In recent years, GSH iswidely used as pharmaceutical, food additives and cosmetic.In this study, C. utilis SZU07-01which could accumulate GSH intracellularly wasselected for preparation of selenium-enriched yeast. Aiming at high performance (highorganic selenium content and high glutathione content) of the selenium-enriched C.utilis preparation, together with the application of the yeast, the experiments were designed and conducted in three aspects as follows:Firstly, the effects of sodium selenite concentration and addition mode on thepreparation of selenium-enriched C. utilis with high performance (high organicselenium content and high glutathione content) were investigated in flasks and a5Lfermentor, respectively. It was found that selenium-enrichment C. utilis could beachieved under sodium selenite concentration of15mg/L, but one-shot addition ofsodium selenite with high concentration had poisonous effect on yeast cells.Accordingly, the better culture mode for efficient preparation of selenium-enriched C.utilis was obtained with batch addition of sodium selenite as follows:10mmol/LL-methione was added at0h, together with10mg/L and5mg/L sodium selenite wasadded at12h and15h, respectively. Under this culture mode, GSH of172.3mg/L andorganic selenium content of1194μg/g was achieved.Secondly, preparation of selenium-enriched C. utilis was conducted underfed-batch fermentations. It was indicated that cell growth, GSH production andselenium-enriched C. utilis performance were improved. The effects of fed-batchfermentation under constant, exponential and polynomial feeding strategies onselenium-enriched yeast were investigated. Aiming at higher organic selenium contentand higher Se biotransformation ratio, the polynomial feeding was proven the optimalfeeding approach. Based on the results above, the effects of sodium selenite additionconcentration and addition mode on selenium-enriched C. utilis preparation were furtherstudied. It was shown that high biotransformation ratio of Se was obtained by addinglow concentration of sodium selenite. However, organic selenium content wasmaintained at a low level. Besides, high concentration of sodium selenite had inhibitoryeffect on cell growth, GSH production and biotransformation ratio of Se. For thesereasons, the optimal addition concentration of sodium selenite was60mg/L.Furthermore, the effects of sodium selenite addition mode under one-shot, batch, andcontinous feeding strategies on preparation of selenium-enriched C. utilis were studied.It was shown that continous feeding of sodium selenite was more suitable forselenium-enriched C. utilis preparation, and the intracellular GSH content (IGC) and theorganic Se content reached687.6mg/g and1143.1mg/g, respectively, under the optimal culture conditions.In the end, the effects of selenium-enriched C. utilis on the activities of enzymesrelated to antioxidant capacity in rats were investigated. It was indicated thatsupplementation with selenium-enriched C. utlis in diet could promote the growth of SDrats, and also significantly increased the activities of GSH-Px, SOD and CAT, comparedto the control. Therefore, selenium-enriched C. utlis could enhance antioxidant capacityof rats and protecting cells against damages caused by free radicals and lipid peroxides.Meanwhile, selenium-enriched C. utlis could enhance the transformation capacity oflymphocyte and improve the immune function in rats.