AGRO 127

Chemical and physical properties of pretreated biomass that affect enzyme accessibility and digestibility

Mark F. Davis, mark_davis@nrel.gov, Claudia Ishizawa, claudia_ishizawa@nrel.gov, Tina Jeoh, tina_jeoh@nrel.gov, William S. Adney, william_adney@nrel.gov, Michael E. Himmel, mike_himmel@nrel.gov, and David K. Johnson, David_Johnson@nrel.gov. National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO 80401
Understanding the chemical and physical factors governing biomass recalcitrance to enzymatic deconstruction is critical to achieving the biomass refinery concept. Current pretreatment technologies utilizing thermochemical processing to improve the accessibility of the cellulose fraction of biomass to cellulase enzymes tend to be harsh and can result in the accumulation of toxic inhibitors that affect the fermentation process. If we are to replace, or improve current pretreatment regimes with more benign and thus less costly procedures, an in-depth understanding of barriers to cellulase enzymes becomes critical. In this presentation, we examine select chemical and physical properties of pretreated biomass and their impact on enzyme accessibility and ultimately, the conversion of biomass to ethanol. We will discuss how physical parameters such as porosity and cellulose morphology as well as chemical parameters such as hemicellulose and lignin removal affect enzymatic conversion rates. Our findings, based on cellulose hydrolysis and enzyme adsorption data, confirm that improving cellulose accessibility to enzyme attack is critical to efficient conversion. While the removal of xylan and lignin to levels of around 80% increases the digestibility of corn stover, at higher levels of xylan and lignin removal, digestibility was seen to decrease significantly. The study presented here represents an on-going effort at the National Renewable Energy Laboratory to understand biomass recalcitrance using a combination of physical and chemical characterizations and to elucidate the effect of pretreatment processes on cellulase-substrate interactions in enzymatic studies using purified cellulases.