Shishir Chundawat
,
Chemical Engineering and Materials Science, Michigan State University, Lansing, MI
Bryon S. Donohoe
,
Biosciences Center, National Renewable Energy Laboratory, Golden, CO
Thomas Elder
,
Southern Research Station, USDA-Forest Service, LA
Per Askeland
,
Composite Materials & Structures Center, Michigan State University, East Lansing, MI
Ramin Vismeh
,
Chemical Engineering and Materials Science, Michigan State University, Lansing, MI
Umesh Agarwal
,
USDA-Forest Products Laboratory, Madison, WI
James F. Humpula
,
Chemical Engineering and Materials Science, Michigan State University, Lansing, MI
Lekh Nath Sharma
,
Chemistry and Biochemistry, Baylor University, Waco, TX
Rebecca Garlock
,
Chemical Engineering and Materials Science, Michigan State University, Lansing, MI
A. Daniel Jones
,
Chemical Engineering and Materials Science, Michigan State University, Lansing, MI
Kevin Chambliss
,
Chemistry and Biochemistry, Baylor University, Waco, TX
Michael E. Himmel
,
Chemical and Biosciences Center, National Renewable Energy Laboratory, Golden, CO
Venkatesh Balan
,
Chemical Engineering and Materials Science, Michigan State University, Lansing, MI
Bruce Dale
,
Chemical Engineering and Materials Science, Michigan State University, Lansing, MI
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.
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