11-01: Assessing the cellulase accessibility of lignocellulosic substrate before and after pretreatment

Renewable fuels derived from lignocellulosic biomass offer a promising alternative to conventional fuels. However, this bioconversion process is significantly hindered by the recalcitrance of biomass and thereby requires a pretreatment stage. Dilute acid pretreatment, and steam explosion are two of the leading pretreatment technologies and future improvements require a better understanding of the fundamentals of biomass recalcitrance. Cellulose accessibility-porosity of lignocellulosic biomass has been proposed to have a major structural impact influencing the hydrolysis of substrates by cellulases. Herein, we have utilized a Simons’ Stain technique for the determination of the available surface area of native and pretreated Poplar along with Nuclear Magnetic Resonance cryoporometry to determine pore size distributions as it changes during dilute acid pretreatment and autohydrolysis. Results show that pretreated Poplar has larger accessible surface area and higher cellulose conversion compared to untreated one. Both these techniques indicate that as the severity factor is extended the pretreated Poplar has increased accessible surface area which correlates with enzymatic hydrolysis results. Simons’ Stain, NMR studies and enzymatic hydrolysis studies indicate that for the conditions studied, dilute acid pretreatment is much more effective than steam explosion for Poplar in increasing cellulose accessibility, pore size and enzymatic deconstruction. All these results show that the Simons’ Stain and NMR cryoporometry are effective and valuable diagnostic tools to evaluate cellulose accessibility and select fundamentals of recalcitrance.