Effect of degradation products on Saccharomyces cerevisiae GLBRCY128 in the RaBIT (Rapid Bioconversion with Integrated recycle Technology) process using AFEXTM corn stover

The RaBIT (Rapid Bioconversion with Integrated recycling Technology) process was developed to create a lignocellulosic biomass to biofuel process with greatly reduced processing times and effective biocatalyst (enzymes and microbes) recycling.  Reducing the processing time increases the volumetric ethanol productivity, while reducing capital costs.  Enzyme recycling by transferring unhydrolyzed solids along with bound/adsorbed enzymes reduces enzyme usage by 50%.  High cell density yeast fermentations and cell recycling of cells are likewise promising.    However, upon recycling xylose consumption decreases despite increased cell mass.  We attribute this to three key factors: nutrient deficiency, degradation product inhibition, and cell aging.  By measuring the concentration of cells with intact outer membranes (a proxy for live cell concentration), we have shown that significant cell death occurs during the xylose consumption phase.  In this presentation, we investigate the effects that biomass degradation products have on fermentation performance and the cell population and show how fermentation potential can be maximized based on these insights.