Optimization Of Fuel Ethanol Production From Fresh Sweet Potato By Low Temperature Double-enzymatic Method And Simultaneous Saccharification And Fermentation

Sweet potato is one of the major feedstock for the fuel ethanol production in China. The cultivation of sweet potato in China has a wide range of distribution. Its drought resistance and adaptability are very strong and a kind of easy-to-high-yield crop. It is widely used as a raw starch to produce ethanol, convenience and high productivity. Double-enzymatic method, low temperature cooking & steaming technique and simultaneous saccharification and fermentation (SSF) were used, and the technological conditions of Fuel ethanol production from fresh sweet potato have been established in this paper. In the first part of the experiment, the better feedstock for fuel ethanol production were found by the investigation of Content of fermentation sugars in sweet potato and Fermentation efficiency and Viscosity of fermentation mash of five varieties of sweet potato. In the second part of the experiment, Effects of the pretreatment conditions including the optimize conditions of liquefaction, and kinds of icons and enzymes on the dextrose equivalent value (DE) and syrup viscosity were also tested. The most favorable pretreatment conditions were established. In the third part of the experiment, the optimum fermentation conditions of fresh sweet potato were obtained with simultaneous saccharification and fermentation technique.The following are the summary of the paper.(1)NS 007 were the better feedstock for ethanol production, which had the highest Content of fermentation sugars, highest Fermentation efficiency, the higher Yield of fermentation sugars in unit area ,and the lower viscosity of fermentation mash (771 mPa·S).(2)The optimum liquefaction conditions were summed up through single factor tests and orthogonal tests as follows. Liquefaction pH 5.0, the dosage of liquefaction enzyme 50 KNU/kg, the liquefaction temperature 95℃, the liquefaction time 25 min. There is no significant difference in the investigation of the effects of kinds of icons on the dextrose equivalent value (DE).The amounts of pectinase and cellulose added in saccharification were 40 U per g syrup and 0.5 U per g syrup, respectively. The highest DE of 98.45 and the lowest viscosity of 4.2×10 mPa·S were obtained by the most favorable pretreatment conditions, while those of 91 and over 1.0×105 mPa·S was produced by treatment conditions which did not add pectinase and cellulose.(3)The best fermentation conditions were summed up through single factor tests and orthogonal tests as follows:the use level of saccharifying enzyme as 1.5 AUG per g starch, the ratio of water and fresh sweet potato and water as 1.5, yeast inoculation quantity as 5%, and 25 h fermentation time. Results of ethanol fermentation from sweet potato as follows.The average of ethanol concentration (w/%) was 9.32, the average of Final reducing sugar concentration (w/%) was 0.61,the average of Final total sugar concentration(w/%) was 1.71,the average of Fermentation efficiency(P/%) was 90.90,and the average of Final pH value was 3.92.