Pichia Stipitis Adaptation And Xylose Fermentation In Hydrolysate

Lignocellulosic biomass of agricultural residues, which contains abundant carbohydrates and is renewable but not in competition with food sources, is an attractive feedstock for producing liquid fuels. However, xylose utilization is one of the key obstacles being tackled. The issues that this work attempted are:screening a xylose fermentation strain with good performance in hydrolysate fermentation by adaptation in media which contain gradually increasing concentrations of inhibitors of steam-exploded corn stover hydrolysate, and advancing a new technic route to ferment both glucose and xylose in hydrolysate efficiently. The main results are as follows:P1, P2 and C1 were adapted by the media with gradually increasing proportion of hydrolysate respectively. Ethanol yields of the adapted strains P1-08, P2-08 were 82.1% and 77.7% respectively, and xylose consumption ratios were 94.1% and 94.0% respectively in high nutrient condition, further adaption with lower organic nitrogen source containing and supplementing inorganic nitrogen source received P1-28, of which ethanol yield and xylose consumption ratio were 80.1% and 92.0% when the proportion of 80% hydrolysate was contained and the concentration of formic acid and acetic acid were 1.9 g l-1 and 2.0 g l-1. Therefore, Pichia stipitis was capable of fermenting xylose to ethanol with the presence of inhibitory components through adapting to steam-exploded corn stover hydrolysate.Fermentation started at initial xylose concentrations of 30,45 and 60 g l-1, and it was found that PI-08 and P2-08 had higher average ethanol productivities and lower average biomass productivities when the initial xylose concentrations were 45 and 60 g l-1 respectively. Carbon recovery was 89.7% and 48.5% carbon was converted to ethanol in the fermentation of 51.6 g l-1 xylose hydrolysate for 36 h using P1-28, according to carbon balance and carbon metabolic effluence analysis.S. cerevisiae fermentation broth containing 63.2 g l-1 ethanol was collected and distilled by vacuum distillation. Ethanol concentration of the distilled broth was 0.47 g l-1, the percentage of removed ethanol was 99.3%, and acetic acid concentration was 2.91 g l-1 when concentrated 2 times. Xylose with the concentrations of 55.4 g l-1 and 84.4 g l-1 in the distilled broth was fermented to ethanol with the concentrations of 20.4 g l-1 and 30.2 g l-1, and the ethanol yields were 80.2% and 79.8% respectively when 90% of the xylose was utilized. It was fully demonstrated that xylose in S.cerevisiae culture broth can be effectively used by adapted P. stipitis using the above new technic route, solving the problem of xylose utilization efficaciously in the process of ethanol production from lignocellulosic materials.