Screening High Protein And High RNA Yeast Strain And Optimization Of Fermentation Process For Yeast Extract

Yeast extract is a kind of nature product which mainly use yeast cells as raw materials.Its main ingredients include peptides,free amino acids,nucleotides,and a small amount of B vitamins and minerals,etc.So it has good nutritional properties,flavor characteristics and features.The good nutritional properties come from peptides and amino acids which were hydrolysis by yeast intracellular proteins and flavor characteristics come from the decomposition products of RNA.So the content of RNA and protein of yeast strains can directly affect the quality of yeast extract.This article mainly has carried on the following several aspects work:1.The yeast strains preserve by freeze-dried bacteria chamber pipe from Angel Yeast Co.,Ltd were screened by shake flask culturing and then second screened by 30 L jar fermentation.At last,obtaining the best performance yeast strain of J-5.The results showed that the content of protein and RNA could reach 62.4%and 9.86%,respectively,and the dry cell weight reached 41.58 g/L.The strain J-5 possessed weak fermentation performance and low trehalose.The strain was finally identified as Saccharomyces cerevisiae by its morphological,physiological-biochemical characteristics and 26s rRNA gene sequence homology.2.Saccharomyces cerevisiae J-5 was used as the producing strain to investigate the optimum culture conditions and the optimum fermentation medium.The results showed that the optimal conditions were pH 5.0,cultural temperature 30?and rotate speed200 r/min.The optimal fermentation medium was obtained as following:glucose 5%,yeast extract 1%,corn syrup 1.5%,?NH₄?₂SO₄ 1.5%,KH₂PO₄ 0.2%.When strain J-5grown in the optimzed fermentation medium,the content of RNA reached 12.6%and dry cell weight reached 12.2 g/L.3.Using 10 L fermenter,the effects of aeration rate,fermentation speed,inorganic salts and amino acids on producing RNA were also studied.The optimum aeration rate was 1 vvm,fermentation speed was 400 r/min.By shake flask experiments investigated inorganic salts with FeSO₄ and amino acids with Asp,Gln,Ser and Leu can improve the content of RNA and the production of dry cell weight.The addition of amino acids is Ser 0.3%,Gln 0.3%,Asp 0.05%,Leu 0.05%.Finally,the optimum feeding rate of FeSO4 and the impact of FeSO4 and amino acids were explored in the fermentation process.The results showed that the optimal feeding rate of FeSO₄ is 2 g/h,the content of RNA and biomass have improved greatly when adding FeSO₄ and amino acids.Compared with the control group,the biomass increased by 28.3%,18.48%;RNA were increased by 18.9%,7.62%.