Monday, May 5, 2008
6-34

Enzymatic Saccharification of Xylooligomeric Compounds Present in Hydrolysates from Neutral and Acidic Pretreatments of Lignocellulosic Biomass

Michael J. Selig1, William Michener2, Roman Brunecky1, Justin Sluiter2, and Stephen R. Decker1. (1) Chemical and Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, (2) National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401

The complete removal of xylan from the cell wall matrix has long been a key target for improving the efficacy of enzymatic saccharification of lignocellulosic biomass. In consideration of this a number of high-temperature dilute acid and neutral pretreatment schemes have been employed. Typically, the high pretreatment severities needed to achieve complete conversion of xylan to monomeric sugars result in some sugar degradation. It is also known that some of these degradation products have inhibitory effects on subsequent fermentation processes; often requiring costly conditioning steps to address. In this work, we looked towards lower severity pretreatment conditions to reduce sugar degradation losses and the production of toxic by-products. At lower severities, the efficiency of xylan removal can remain high, although the bulk of hydrolyzed xylan remains in more complex xylooligomeric (XO) forms. In this study, we utilized LCMS to determine the numerous simple and branched XO forms that can exist in low severity pretreatment hydrolysates. We also investigated the manner in which the XOs can be hydrolyzed enzymatically to achieve complete conversion to xylose.  We demonstrated that many commercially available enzyme preparations can hydrolyze the majority of XO compounds, although these preparations often have only trace amounts of the activities necessary for optimal conversions; leading to slow conversion times and increased protein requirements. Additionally, we will present hydrolysate digestion studies using purified hemicelluloytic enzymes to better understand which activities are crucial to complete XO hydrolysis; these in include endoxylanase, beta-xylosidase, acetyl xylan esterase, ferulic acid esterase, arabinofuranosidase  and xyloglucanase activities. 




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