Shishir P. S. Chundawat1, Venkatesh Balan1, A. Daniel Jones2, Kevin Chambliss3, Lekh Sharma3, Ramin Vismeh4, Rebecca Garlock1, Thomas Elder5, Per Askeland6, and Bruce E. Dale1. (1) Department of Chemical Engineering and Material Science, Michigan State University, 2527 Engineering building, East Lansing, MI 48824, (2) Department of Biochemistry and Molecular Biology and Department of Chemistry, Michigan State University, East Lansing, MI 48824, (3) Department of Chemistry & Biochemistry, Baylor University, Waco, TX 76798-7264, (4) Department of Chemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, (5) Southern Research Station, USDA-Forest Service, 2500 Shreveport Highway, Pineville, LA 71360, (6) Composite Materials & Structures Center, Michigan State University, 2527 Engineering building, East Lansing, MI 48824
The severity (time, temperature and ammonia loadings) of AFEX (Ammonia Fiber Expansion) pretreatment is thought to play an important role on modification of the Lignin-Carbohydrate-Complex (LCC) Bridge. The LCC bridge is comprised of hemicellulose side-chains (e.g. acetyl groups, uronic acid and arabinose residues) and phenolic aromatic moieties (e.g. ferulic, cinnamic, p-coumaric) that help strongly bind hemicellulose to core lignin. Hence, the severity of AFEX pretreatment would be very closely linked to the digestibility of the treated plant cell wall. The optimum composition and concentration of individual enzyme activities required to achieve higher glucan and xylan conversions is likely dependent on the cell wall ultra structure and ultimately, the severity of pretreatment.
We examined the morphological and ultra structural changes in the corn stover cell wall upon AFEX pretreatment of varying severities, using an environmental scanning electron microscope (eSEM), laser scanning confocal microscope (LSCM) and an atomic force microscope (AFM). The chemistry of AFEX was better understood through identification and quantification of degradation compounds produced during the process. Solvent extraction of the untreated and AFEX treated corn stover was carried out using an accelerated solvent extractor (ASE) for subsequent LC/GC-MS analysis. MALDI-TOF-MS analysis was conducted to determine the degree of polymerization and acetylation of arabino-xylosaccharides produced during AFEX. Quantification of arabino-xylosaccharides was conducted by measuring sugars released during acid hydrolysis of the ASE extract. The overall goal of this project was to study the effect of varying AFEX pretreatment severity on the cell wall ultra structure and its related degradation reactions.
