| Biomass ethanol is the hotspot in the world at present,due to the depletion of fossil fuels.Ethanol as a clean and safe liquid fuel,it has drawn much attention nowadays.It is of great significance to vigorously promote the research on biomass ethanol for the sustainable development of economy and society.In this study,Candida tropicalis CICC1779 was used to produce ethanol by using hydrolyzate of cassava residue to improve the utilization value of waste cassava residues.By mutagenesis screening of the yeast and metabolic flux analysis,high yields of ethanol can be achieved.In this paper,we mainly study the single factor test of hydrolysis conditions of cassava residue,and then used response surface analysis to optimize it.Then the yeast was mutated by UV and domesticated selection,and we used it to fermentation the Cassava residue hydrolyzate.Finally,the tank ferment experiment was carried out,then constructwd the metabolic networks and listed the relevant metabolic equations,and the changes in substrate,product,and cell concentration was measured.Then their metabolic flux and kinetic models were analyzed.The main results are as follows:(1)Based on the single factor experiment of enzymolysis,the enzymolysis process was optimized by response surface,and the optimal enzymolysis process was as follows: hydrolysis temperature was 36 ℃,initial p H=4,hydrolysis time was 42 min,substrate concentration was 80 g/L,and the 10 g of cassava residues was hydrolyzed into 6±0.6 g of reduced sugar,which included 4 ±0.6g of glucose and 2±0.7 g of xylose,and the yield of reducing sugar reached 75% of the theoretical value.(2)The original yeast(Candida tropicalis CICC1779)was mutated by UV,followed by Dunaliella tubule screened and by TTC colorimetric screened.Finally a mutant strain T70-2 was obtained.(3)Based on the single factor experiment of ethanol production from cassava residue hydrolyzate,the optimal fermentation conditions were obtained through response surface optimization: fermentation temperature 34℃,initial p H=4,fermentation speed 150 r/min,inoculation volume 10%.Ethanol production was tested as 22.15 ± 0.28 g/L,and xylose utilization reached 80%,an increase of 42.6% over the original strain.(4)The effect of different oxygen transfer coefficient(KLα)on fermentation performance was studied by fermentation of cassava residue hydrolyzate.The results showed that the fermentation efficiency was the best when KLα was 85 at 72 h and the ethanol concentration was 23.14 g/L,and the cell density was 5.74 g/L.The concentration of cell was 6.45 g/L and the concentration of ethanol was 25.43 g/L under aeration and stirring control.The amount of residual sugar was 2.62 g/L(Basically were xylose),and the sugar alcohol conversion at this time was 0.42 g/g.Xylose utilization reached 87%,an increase of 48% over the original strain.After it was breeded,strain could make better use of cassava residue hydrolyzate to produce ethanol,which laid the foundation for expanding the comprehensive utilization of potato fiber residue... |
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