Tuesday, April 30, 2013
Exhibit Hall
Current technology for deconstruction of crystalline cellulose that is beautifully amalgamated with hemicellulose and lignin in lignocellulosic biomass employs high enzyme concentrations that challenge making lignocellulosic ethanol commercially viable as enzymes are expensive. Cellulase activity drops considerably over time at low enzyme loadings due to inhibitory products and other less well understood factors. Therefore, pretreated Switchgrass (Panicum Virgatum) and Poplar (Populus Trichocarpa) was enzymatically hydrolyzed at low enzyme loadings to study the kinetics and effects of inhibition caused by products generated during the reaction on specific cellulase activity. The biomass was pretreated at hydrothermal and dilute acid conditions over a range of severities in batch and flowthrough reactors. The pretreated substrates were then subjected to air-drying, freeze-drying, and drying at 45 and 105°C to observe changes in pore size and its effect on sugar yields. Surface characteristics of pretreated substrates were studied by plotting enzyme adsorption isotherms that were supplemented with information from SEM, CFM, water retention values and Simons’ staining techniques. Labeling for CFM was done with fluorescent dyes of the stilbene class which have an affinity for cellulose. Also, CBH1 isolated from T. reesei cellulase was applied alone to support the deconstruction hypothesis. The results will help explain why specific enzyme activity is so low at low enzyme loadings. In addition, they can help us understand whether intermolecular hydrogen bonding in cellulose microfibrils or surface accessibility limitations dominate biomass recalcitrance to enzymes.
Abbreviations: SEM: Scanning Electron Microscopy CFM: Confocal Fluorescence Microscopy CBH1: Cellobiohydrolase I