Xylose Fermentation To Produce Ethanol By Pichia Stipitis

It is an economical and environmentally friendly way to produce ethanol from lignocellulosic materials. Xylose comprises nearly 30% of total sugars in lignocellulosic hydrolysates. This study focuses on the process of ethanol production of xylose fermentation by Pichia stipitis as well as strain improvement. The results are listed as follows:(1) Different xylose concentration and inoculum had effect on fermentation. High xylose concentration caused low substrate utilization efficiency. Ethanol production and yield could be improved by increasing inoculum appropriately. The suitable substrate concentration was 20 g/l with the suitable inoculum of OD600=2. Ethanol inhibited the fermentation process with the highest concentration of ethanol Pichia stipitis can tolerate of 50 g/l.(2) Fermentation in bioreactor performanced better than flask. Ethanol production and yield were 6.85 g/l and 0.38 g/g in bioreactor which were 1.3 times and 1.5 times of that in flask, respectively. Fed-batch fermentation could solve the problem that high xylose concentration leading to low utilization efficiency.(3) In sugar mixture of 20 g/l fermentation, glucose increased the average xylose consumption rate to some extent and thereby reduced culture time. In addition, glucose can improve ethanol productivity of fermentation process.(4) Ethanol production from rice straw hydrolysates by Pichia stipitis was investigated. The culture time was 70~80 h with the maximum ethanol yield of 0.17 g/g. Moreover, the final ethanol concentration in hydrolysate with dregs was 1.2 times as much as that in hydrolysate without dregs.(5) For strain improvement, UV mutation and NTG mutation were introduced. UV-1 strain and UV-4 strain were obtained by UV mutation with increased ethanol yield by 17.93% and ethanol production by 13.67%. NTG-2 strain was obtained by NTG mutation with improved ethanol production by 8.50% and ethanol yield by 3.82%.