Simultaneous Saccharification and Fermentation of Switchgrass by Thermotolerant Kluyveromyces Marxianus IMB3: Effect of Enzyme Loading, Temperature and Operating Mode

Hydrothermolysis-pretreated Kanlow switchgrass was used in simultaneous saccharification and fermentation (SSF) with Kluyveromyces marxianus IMB3 at various enzyme loadings and temperatures.  The pretreated switchgrass contained 57.7% glucan, 5.0% xylan and 35.1% lignin.  Various loadings (0.3, 0.5 and 0.7 mL/g glucan) of the enzyme Accellerase 1500 (Genencor, Rochester, NY) were used in the SSF at 45°C (Accellerase 1500 activity was 82.2 FPU/mL).  The highest ethanol concentration (22.3 g/L) was obtained in SSF with 8% solids and enzyme loading of 0.7 mL/g glucan.  This enzyme loading was used with 8% solids in subsequent SSFs at 37, 41 and 45°C.  The highest ethanol concentration (22.8 g/L) was obtained at 45°C after 96 h, corresponding to 83.9% of the maximum theoretical yield (MTY).  However, ethanol yield was about 79% of MTY in SSF at both 37 and 41°C.   No significant differences in the amount of ethanol produced were observed in the SSF operated in batch or fed-batch modes at 45°C and 12% solids (p > 0.05).  However, the enzyme loading in fed-batch SSF was 33% lower than in batch SSF.  About 32 g/L ethanol (81% MTY) was produced in all batch and fed-batch feeding strategies.