Simultaneous saccharification and fermentation of Kanlow switchgrass by thermotolerant Kluyveromyces marxianus IMB3: The effect of enzyme loading, temperature and higher solid loadings

Switchgrass (Panicum virgatum) was subjected to hydrothermolysis pretreatment and then used to study the effect of enzyme loading and temperature in a simultaneous saccharification and fermentation (SSF) with the thermotolerant yeast strain Kluyveromyces marxianus IMB3 at 8% solid loading. Various loadings of Accellerase 1500 between 0.1 and 1.1 mL g-1 glucan were tested in SSF at 45 C (activity of enzyme was 82.2 FPU mL-1). The optimum enzyme loading was 0.7 mL g-1 glucan based on the six different enzyme loadings tested. SSFs were performed at 37, 41 and 45 C with an enzyme loading of 0.7 mL g-1 glucan. The highest ethanol concentration of 22.5 g L-1 was obtained after 168 h with SSF at 45C, which was equivalent to 86% yield. Four different batch and fed-batch strategies were evaluated using a total solid loading of 12% (dry basis). About 32 g L-1 ethanol was produced with the four strategies, which was equivalent to 82% yield.