Monday, May 4, 2009 - 10:30 AM
3-05

Ultra-structural and physicochemical modifications within ammonia pretreated lignocellulosic cell walls that influence enzyme accessibility

Shishir Chundawat1, Bryon S. Donohoe2, Thomas Elder3, Per Askeland4, Ramin Vismeh1, Umesh Agarwal5, James F. Humpula1, Lekh Nath Sharma6, Rebecca Garlock1, A. Daniel Jones1, Kevin Chambliss6, Michael E. Himmel7, Venkatesh Balan1, and Bruce Dale1. (1) Chemical Engineering and Materials Science, Michigan State University, Great Lakes Bioenergy Research Center (GLBRC), 3900 Collins Rd, Lansing, MI 48910, (2) Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401, (3) Southern Research Station, USDA-Forest Service, LA, (4) Composite Materials & Structures Center, Michigan State University, 2527 Engineering building, East Lansing, MI 48824, (5) USDA-Forest Products Laboratory, Madison, WI, (6) Chemistry and Biochemistry, Baylor University, One Bear Place #97348, Waco, TX 76798-7348, (7) Chemical and Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401

The development of an economically viable and environmentally sustainable bio-based chemical industry has been impeded due to the native recalcitrance of lignocellulosics to chemical and biological processing. Lower severity ammonia based pretreatments (e.g. AFEX) and minimizing enzyme usage could help reduce processing costs. However, unlike other pretreatments AFEX does not extract lignin and hemicellulose into separate liquid fractions. Instead, AFEX enhances enzymatic digestibility through certain ultra-structural and chemical modifications within the cell wall that are currently not well understood.

An important goal of this research was to identify the major ultra-structural and chemical modifications incorporated within lignocellulosic cell walls during AFEX using several microscopic, spectroscopic and spectrometric techniques. High resolution microscopic (SEM, TEM) and 3D-EM-Tomographic studies indicate an ultra-structural alteration of AFEX treated cell walls via formation of a nanoporous tunnel-like network. Closer analysis (via ESCA, AFM and confocal fluorescence microscopy) of outer cell wall surfaces shows heterogeneous deposits rich in AFEX cell wall extractives. Raman spectral data indicates conversion of cellulose I to III is intricately dependent on AFEX pretreatment conditions. More than 45 degradation products have been quantified using LC-MS/MS and GC-MS. Some of the major degradation products include organic acids, aromatics, phenolic acids and amides.

A fundamental understanding of physicochemical modifications incorporated within lignocellulosic cell walls during pretreatment and its effect on enzyme accessibility are critical to further advancements in reducing cell wall recalcitrance to bioprocessing. This understanding would be critical to re-engineer plant cell walls, hydrolytic enzymes and ethanologenic microbes amenable for cellulosic biorefineries.