Simultaneous Saccharification and Fermentation of Pretreated Switchgrass Using Thermotolerant IMB Strains of Kluyveromyces marxianus

Abstract

Simultaneous Saccharification and Fermentation of pretreated switchgrass were used to evaluate the ethanol production characteristics of five strains of thermotolerant K. marxianus at 45 ﾺC compared to S. cerevisiae D5A at 37 ﾺC. Further experiments were performed to investigate the effects of pH and enzyme loading on SSFs with K. marxianus IMB 3 and S. cerevisiae in terms of ethanol yields and fermentation times. SSFs with the five IMB strains of K. marxianus converted between 67% and 80% of glucan to ethanol. However, S. cerevisiae D5A at 37 ﾺC converted 92% of glucan to ethanol and only IMB 3 had comparable yields. Decreasing the initial pH of the SSF buffer from 5.5 to 4.8 resulted in decreased ethanol yields produced by S. cerevisiae D5A from 92% to 78%. Controlling the pH of SSF with IMB 3 at 45 ﾺC by addition of KOH in a stirred bioreactor resulted in an increase in ethanol yield from 80% to 83% by reducing inhibition caused by acetic acid. Reducing the enzyme loading from 15 FPU/g glucan in SSFs with IMB 3 and S. cerevisiae D5A resulted in significant decreases in ethanol yield.