Study On Fed-batch Fermentation Of High Concentration Ethanol With S.cerevisiae GGSF16

There is extensive production of cassava in Guangxi,in recent years,cassava fuel ethanol production has achieved significant results,but the fermented liquor only reached 14%(v/v),residual sugar concentration was high and fermentation time was too long.To solve a series of problems in the fermentation process and achieve high concentration ethanol fermentation,with high-yield ethanol yeast GGSF16 as strain,ethanol fed batch fermentation experiment was carried out using YEPD(Yeast Extract Peptone Dextrose Medium)as model fermentation medium,trying to establish an effective batch feeding strategy and providing experimental basis for cassava and others fed batch fermentation.The contents and results of this study are as follows:(1)Determination of initial sugar concentration of high concentration ethanol fed batch fermentationEthanol batch fermentation was studied at 340 g/L total sugar concentration and different initial sugar concentration(200,220,240,260 g/L),indicating that the high residual sugar?long fermentation time and the decrease of the total sugar fermentation efficiency at 340 g/L total sugar concentration was mainly resulted in the inhibition of high initial sugar concentration.The results showed that 240 g/L initial sugar concentration batch fermentation achieved the best at the lower initial sugar concentration range.Finally,the fermentation efficiency was 91.95%,the yield of ethanol was higher and the inhibition of cells was less,indicating that 240 g/L initial sugar concentration was suitable for high concentration ethanol fermentation.(2)Study on feeding time and component of feeding medium of high concentration ethanol fed batch fermentationMethylene Blue dye Reduction Test(MBRT)was used to estimate the yeast vitality during ethanol batch fermentation,and the optimum feeding time of ethanol fed batch fermentation was determined by combining sugar consumption and ethanol production.The results showed that MBRT was effective and feasible to estimate the yeast vitality and be an index of feeding time during ethanol fed batch fermentation.When the decolorization rate of methylene blue was the largest in the middle of logarithmic(about 10 h),the fermentation effect was the best and the ethanol concentration,ethanol yield and total sugar fermentation efficiency were 152.28 ± 2.37 g/L,2.46 ± 0.04 g/(L·h)and 89.84%,respectively.The results showed that the yeast extract and peptone added into the feeding solution could supplement the nutrient needed for the yeast cells to make yeast maintain high vigor,and the fermentation time was shortened by 12 h compared with the pure sugar solution.The ethanol yield was improved by about 20.5 %.(3)Intermittent fed batch fermentation of high concentration ethanolThe results showed that feeding once during fed batch fermentation could cause great fluctuation of the fermentation environment and the dilution effect on the bacteria,which resulted in lower total sugar fermentation efficiency(76.09%).Feeding twice has higher fermentation efficiency(77.46%),but the feeding time should not be too late,otherwise yeasst had lower vitality and use glucose slowly,resulting in lower fermentation efficiency(75.98%)and higher residual sugar(4.1 g/L).The effect of repeated intermittent feeding was better than that of secondary feeding,and the final ethanol concentration and total sugar fermentation efficiency were 140 g/L and 80.02%,respectively.It can avoid the effect of the feeding on the fermentation environment.However,during the batch feeding batch,too many feeding times will cause the great fluctuation of the fermentation environment frequently and lower the fermentation efficiency.Finally,the intermittent fed batch fermentation was better,so we can consider continuous feeding fermentation.(4)Continuous fed batch fermentation of high concentration ethanol in 5 L fermenterThe continuous fermentation process was carried out,showing that the fermentation time was shortened 12 h at a constant feeding rate compared with the high concentration ethanol batch fermentation,and the ethanol yield and the total sugar fermentation efficiency were both increased by about 64.1% and 9.5% respectively.The effect of the variable feeding strategy was obviously better than that of the constant rate feeding strategy,compared with the constant speed feeding strategy,the ethanol yield and the total sugar fermentation efficiency were both increased by 6.5%,4.2%;According to the ability of sugar consumption,the variable speed feeding rates were determined,maximizing the yeast fermentation capacity and avoiding excessive residual sugar concentration caused by inappropriate feeding strategy.Finally,ethanol concentration and total sugar fermentation efficiency were 143.52 g/L and 83.96%,respectively,which were 17.6% and 18.5% higher than those of batch fermentation.