Simultaneous saccharification and fermentation of switchgrass by thermotolerant Kluyveromyces marxianus IMB3: Effect of enzyme loading, temperature and operating mode

Scope and Method of Study: The objectives of this research were to determine the optimum enzyme (Accellerase 1500, Genencor International, NY, USA) loading, temperature and operating modes (batch and fed-batch) on ethanol production by simultaneous saccharification and fermentation (SSF) of pretreated Kanlow switchgrass using thermotolerant Kluyveromyces marxianus IMB3. Hydrothermolysis pretreatment of switchgrass was used. Also, 8% solids (dry basis, db) loading was used for the effect of enzyme loadings and temperatures tests. Various loadings of Accellerase 1500 (0.3, 0.5 and 0.7 mL g -1 glucan) were used in SSF at 45°C (activity of enzyme was 82.2 FPU mL-1). Then, SSFs were performed at 37, 41 and 45°C with the optimum enzyme loading. Finally, four different batch and fed-batch strategies were evaluated at the optimum enzyme loading and temperature with a total solid loading of 12% (db).;Findings and Conclusions: The optimum enzyme loading was 0.7 mL g -1 glucan in SSF with 8% solids at 45°C, which resulted in the highest ethanol concentration of 22.3 g L-1. This was equivalent to 85% maximum theoretical yield (MTY). For the effect of temperature experiment, the highest ethanol concentration of 23.0 g L-1 (86.3% MTY) was obtained in SSF with 8% solids at 45°C compared to about 20 g L -1 ethanol (77% MTY) obtained at both 37°C and 41°C. In addition, the results showed that about 32 g L-1 ethanol (81% MTY) was produced with a total solid loading of 12% (db) in all batch and fed-batch SSFs strategies. No significant differences in the amount of ethanol produced in batch or fed-batch operating modes were observed in the range of solids and enzyme loadings used (p > 0.05). Moreover, the results also showed that with fed-batch mode and 12% solids (db), the enzyme loading can be decreased by 33% of the optimum loading for batch process.