Bioethanol Production From The Dry Powder Of Jerusalem Artichoke Tubers

Jerusalem artichoke,as a non-food crop which has fine adaptability to environment and is tolerant of drought and poor,has tremendous developing potentiality.The tuber of Jerusalem artichoke is rich in inulin which is present about 70%in the dried tuber.As a reserve carbohydrate,inulin can be hydrolyzed to fructose by inulinase and fermented to ethanol.With these advantages,Jerusalem artichoke can be used as a cheap and inexpensive carbohydrate alternative feedstock for bioethanol production.Currently,most studies has used pure inulin or raw extract of Jerusalem artichoke tubers as substrate for bioethanol production,which is costly and has low feasibility of bioethanol industrial production.In our present study,in order to increase the utilization rate of raw materials and develop cost-effective technologies for industrial bioethanol production,the dry powder of Jerusalem artichoke tubers was used directly to produce bioethanol by a recombinant Saccharomyces cerevisiae strain with exoinulinase gene.The results are as follows:1.Pretreatment of fermentation medium and fed-batch method researchDue to the fermentation medium containing the dry powder of Jerusalem artichoke tubers usually has a high viscosity,which is detrimental to high gravity ethanol fermentation,the optimum pretreatment of medium before fermentation and the fed-batch method were investigated in this study.The result showed that heating the fermentation medium at 115? for 20 s before fermentation was the most suitable pretreatment of fermentation medium for ethanol production.The method with fed-batched in two equal amounts at 24 h and 48 h was the most suitable condition for ethanol production by the recombinant S.cerevisiae 6525.Under the condition,the highest ethanol concentration of 79.0 g/L was achieved at 72 h and the ethanol yield was 83.12%.It demonstrated that proper cooking pretreatment and fed-batch fermentation could help solve the high viscosity problem of fermentation medium containing dry powder and had a better performance for high gravity ethanol fermentation.2.Fermentation condition optimizationThe optimum fermentation conditions in flask based on fed batch fermentation were investigated in this study.The result showed that the best fermentation medium was consisted of 240 g/L dry powder of Jerusalem artichoke tubers and 10 g/L yeast extract.The most suitable technological parameters of ethanol fermentation was:inoculation 10%,medium volume 50%,pH 4.5,34?,and 180 rpm.Then,scale-up test in 5 L agitating fermentor were carried out based on the optimum conditions of flask fermentation.After 72 h of fermentation,around 84.3 g/L of ethanol was produced in the fermentation liquids,and the ethanol yield is 88.6%.3.The scale-up fermentation of bioethanol productionTaking into consideration the condition for fermentation in flask and fermentor are not all the same,the effect of aeration rate and agitation speed on ethanol production were discussed in 5 L agitating fermentor.The optimum condition obtained was:inoculation 10%,medium volume 50%,aeration rate 0 vvm,pH 4.5,34?,and 240 rpm.Under the condition,the highest ethanol concentration of 88.0 g/L was achieved at 72 h and the ethanol yield was 92.6%.After fermentation condition was optimized in 5 L fermentor,fermentation curves were investigated by using 50 L fermentor and 500 L fermentor.In 50 L fermentor,85.67 g/L of ethanol was obtained within 72 h of fermentation,and the ethanol yield was 90.1%.The parameter variable trend in 50 L fermentor was similar to that in 5 L fermentor.In 500 L fermentor,due to the fermentation medium could not get as good agitation as in 5 L and 50 L agitating fermentor,the end of fermentation was delayed to 84 h.77.00 g/L of ethanol was produced and the ethanol yield decreased to 81.01%.Thus,this study had sought the key difficulties in scale production and provided a basis for industrial ethanol production from the dry powder of Jerusalem artichoke tubers by recombinant S.cerevisiae 6525.