(755a) Enzymatic Deconstruction and Surface Characteristics of Poplar Solids Pretreated in Flowthrough and Batch Reactors Under Aqueous Conditions
Unlike batch operations, flowthrough pretreatment solubilizes lignin and prevents its re-condensation under aqueous conditions, thereby providing a powerful tool for studying pretreated biomass with reduced lignin content as well as to understand how lignin hinders biological deconstruction of cellulose. To compare changes in residual hemicellulose and lignin in flowthrough vs. batch pretreated material, standard poplar was pretreated in liquid hot water (LHW) at a severity factor of logR0= 3.4 and in extremely dilute (0.05%) sulfuric acid (DA) at a combined severity logCS= 2.2 at 140°C and 180°C in flowthrough and batch modes of operation. Glycome profiling and other characterizations were performed on the untreated and pretreated solids to determine the effects of the two pretreatment configurations on biomass deconstruction. Enzymatic hydrolysis of resulting pretreated solids was performed with T. reesei cellulase alone and supplemented with xylanase and/or bovine serum albumin (BSA) in a total of eight combinations to understand their effects on biomass deconstruction. It was expected that BSA supplementation would cause a larger improvement in deconstruction of batch than flowthrough pretreated solids due to the higher lignin content in the former, but remarkably, the opposite effect was observed, suggesting that BSA has a greater role than preventing unproductive binding of cellulase to lignin. Even at a high cellulase loading of 100 mg protein per gram glucan, many of the pretreated solids could not be fully digested. Therefore, additional characterizations to determine surface characteristics for enzyme and BSA interactions with pretreated solids were performed through nitrogen analysis, dye staining for cellulosic surface area, and water retention values for hydrophobicity. 13C-1H HSQC NMR spectroscopy showed that guaiacyl lignin was broken down in flowthrough but not in batch pretreatment. Overall, even though flowthrough and batch are both aqueous pretreatments, they produce materials that react very differently with enzymes.