6-4 The challenges of recycling Saccharomyces cerevisiae for lignocellulosic hydrolysate fermentations
Tuesday, April 28, 2015: 9:45 AM
Vicino Ballroom, Ballroom Level
Cory Sarks1, Mingjie Jin1, Alan Higbee2, Saisi Xue1, Jeff Piotrowski2, Trey K. Sato2, Venkatesh Balan3 and Bruce E. Dale4, (1)Chemical Engineering and Materials Science, Michigan State University, DOE Great Lakes Bioenergy Research Center, Lansing, MI, (2)University of Wisconsin - Madison, DOE Great Lakes Bioenergy Research Center, Madison, WI, (3)Department of Chemical Engineering and Materials Science, Michigan State University, DOE Great Lakes Bioenergy Research Center, Lansing, MI, (4)Chemical Engineering and Materials Science, DOE Great Lakes Bioenergy Research Center, Michigan State University, Lansing, MI
Re-pitching (recycling) yeast cells is a common practice in the sugar cane ethanol and corn ethanol industries.  In these applications, the yeast populations can be recycled for months without decreasing performance.  In contrast, significant performance decreases occur after only three recycle events when using AFEXTM corn stover hydrolysate.  Degradation products resulting from the pretreatment and from the biomass itself are a key difference in ethanol production using AFEX hydrolysate compared to the sugar cane and corn ethanol industries.  Synthetic AFEX corn stover hydrolysate was used to verify that pretreatment degradation products were the main cause for decreased performance by recycled yeast populations.

Quantifying degradation product concentrations in the hydrolysate before and after fermentation during the RaBIT (Rapid Bioconversion with Integrated recycling Technology) process was studied first.  The RaBIT process uses high biocatalyst concentrations and biocatalyst recycling to dramatically reduce enzymatic hydrolysis and fermentation times and also enzyme costs.  Results from this study showed an incomplete mass balance between vanillin and its metabolites suggesting an accumulation of vanillin inside the cells.  Vanillin is known to disrupt cellular membranes and may be a chief cause for decreased performance when yeast are recycled.  Testing of this hypothesis is underway.

To overcome the effects of degradation products on the fermentation, several changes have been implemented in the RaBIT process.  Positive results have been obtained by changing the process time, the process type, and by using a cell separation technique.

AFEX is a trademark of MBI, Lansing, Michigan.