Preparation Of Selenium-enriched Yeast Powder And Its Application In Fruit Wine

Selenium is an essential trace element for the human body,and it plays a variety of physiological functions in the body.As a source of organic selenium,selenium-enriched yeast has higher bioavailability and safety than inorganic selenium,and has a broad application prospect.However,there are few studies on the preparation process of selenium-enriched yeast powder and its application in fruit wine.In this experiment,the selenium-enriched Saccharomyces cerevisiae SY2 isolated from the mulberry orchard in Kaiyang area of Guizhou Province was used as the fermentation strain.The fermentation medium and fermentation conditions were optimized to increase the biomass and selenium conversion rate.The selenium-enriched yeast powder is prepared by drying and spray drying.Finally,the selenium-enriched yeast powder is applied to the brewing of mulberry wine.The effect of different inoculation amounts of selenium-enriched yeast on the quality of mulberry wine is explored,with a view to promoting the selenium-enriched yeast in the food industry application and diversified development of selenium-enriched products provide a reference basis.The main results of the research are as follows:1.Through single factor test,significant factor test and center combination test optimization,it is concluded that the selenium-enriched yeast SY2 fermentation medium composition is:molasses 50.0 g/L,ammonium sulfate 3.0 g/L,potassium dihydrogen phosphate 1.1 g/L,sulfuric acid magnesium 2.0 g/L,thiamine hydrochloride 8.0 mg/L,biotin 0.4 mg/L.The selenium-enriched yeast was cultured in the optimized medium shake flask,and the biomass of the selenium-enriched yeast was7.04 g/L,and the selenium conversion rate was 77.18%,which was increased by 26.9%and 19.7%,compared with YPD culture medium.2.The optimized medium was used for fermentation in a 5L fermentor,and the fermentation process was optimized.The optimum fermentation process for selenium-enriched yeast was:pH 5.0,temperature 30℃,inoculum amount 8%,selenium addition amount 30 mg/L,culture With a cycle of 24 h,the biomass of the selenium-enriched yeast reached 9.78 g/L under this process condition,and the selenium conversion rate was 77.5%.3.On the basis of the most suitable fermentation process,a comparative study was carried out on the two feeding methods of pseudo-exponential feeding(specific growth rateμ=0.193h^-1)and dissolved oxygen feedback feeding（DO>30%）.Compared with the two feeding methods,the biomass,cell yield,and selenium conversion rate of the pseudo-exponential feeding are 20.5%,19.3%,and 7.4%lower than that of the dissolved oxygen feeding.Compared with dissolved oxygen feedback,pseudo-exponential feeding has a higher selenium content of 9.17%,and the fermentation cycle is shorter than that of dissolved oxygen feeding,so the production efficiency of pseudo-exponential feeding is higher.Compared with batch fermentation,the biomass of selenium-enriched yeast with pseudo-exponential feeding and dissolved oxygen feedback feeding increased by 2.12,2.74 times,the yield of bacteria increased by 29.2%,62.6%,and the conversion rate of selenium increased by 6.7%.,12.6%.4.The two drying methods of selenium-enriched yeast were studied respectively.The best process conditions for vacuum freeze-drying are:freezing time is 16 hours,and the best freeze-drying protection agent is 15%skimmed milk powder,5%sucrose,The mixing ratio of 5%trehalose,wet bacteria and protective agent is 2:1.5,and the survival rate of the lyophilized powder yeast prepared under these conditions reaches86.3%.The best process conditions for spray drying in another drying method are:inlet temperature 125℃,air flow rate 600L/h,sampling rate 300 mL/h,and cell concentration 40 g/100 mL.The best wall material for spray drying was selected as 10%skimmed milk powder,and 2%mannitol was added as a protective agent for the highest survival rate of bacteria.Under these conditions,the survival rate of the spray-dried bacterial powder and yeast reached 83.7%,and the yield of the bacterial powder was78.5%.Through the analysis of relevant indicators,it can be known that the two drying methods have their own advantages and disadvantages,and can be selected according to actual needs.5.Using sucrose solution as the substrate,it is determined that the optimum sucrose concentration for rehydration activation of selenium-enriched yeast powder is10%,and the optimum rehydration activation temperature is 38℃.6.Apply the prepared selenium-enriched yeast powder to the brewing of mulberry wine.The selenium content in mulberry wine increases with the increase of the selenium-enriched yeast inoculation amount.When the selenium-enriched yeast inoculation amount is 0.06%,the mulberry wine The selenium content in the selenium is 122.8μg/L,which meets the requirements of relevant standards for selenium content in selenium-enriched fruit wine.Commercial yeast and selenium-enriched yeast were mixed and inoculated at（0.04+0.06）%of the inoculum amount for fermentation and brewing of mulberry wine.Compared with the selenium-enriched yeast alone,the lactic acid content of the obtained mulberry wine increased by 0.303 g/L,which contained volatile flavors.The relative content of esters increased by 2.37%and the relative content of alcohols decreased by 6.81%.The aroma of mulberry wine is more elegant and pure,the flavor is more mellow and soft,and the sensory evaluation is higher.At the same time,other indicators also meet the requirements of relevant standards.