Title: Effects of Extractive Ammonia Pretreatment on the Ultrastructure and Glycan Composition of Corn Stover

Abstract

Lignocellulosic biomass is highly recalcitrant and requires a pretreatment step to improve the enzyme accessibility and fermentable sugar yields during enzymatic hydrolysis. Our previous studies demonstrated the rearrangement of the hydrogen bond network within CIII, makes it “amorphous-like” and facilitates easier glucan chain extraction by enzyme. Also, these changes increase the number of solvent-exposed glucan chain hydrogen bonds with water ~50% lowering the surface-bound cellulase by 60–70%. Also, major chemical modifications to lignin occur via ammonolysis of ester-linked ferulate and coumarate linkage. These apparent ultrastructural changes help the enhancement of cellulase activity resulting in higher production of fermentable sugars during enzyme hydrolysis of EA pretreated corn stover relative to Ammonia Fiber Expansion (AFEX) pretreatment. To understand ultra-structural modifications that occur during EA pretreatment, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to examine untreated and EA-pretreated corn stover in an effort to visualize changes in the biomass resulting from the pretreatment. In addition, Immunofluorescence Microscopy was applied to both untreated and pretreated plant cell walls using glycan-directed monoclonal antibodies to reveal possible changes in the spatial distributions of wall glycan epitopes resulting from EA pretreatment. This evaluation was complemented with glycome profiling to determine the glycan epitopemore » compositions of EA-pretreated cell walls relative to untreated and AFEX pretreated corn stover, where lignin and carbohydrates are not extracted. Distinct differences could be observed in the case of xyloglucan, unsubstituted and substituted pectin- and pectic-arabinogalactan-epitope levels in the plant cell wall after EA pretreatment compared with untreated and AFEX-pretreated walls. Liquid ammonia induced de-lignification of cell wall has helped to clearly identify the glucans that are intact after pretreatment. These studies support some of our hypothesis that liquid ammonia cleaves lignin–carbohydrate ester linkages, partially solubilizing lignin and its associated carbohydrates. Specifically, the imaging studies clearly show that some of the cell wall components are extracted as a separate liquid stream during the EA process, thereby creating porous, interconnected tunnel-like networks in the plant cell walls thereby providing better access of carbohydrate polymers to enzymes and thereby increasing the sugar yield from the EA-pretreated biomass.« less

Authors:

Avci, Utku ^[1]; Zhou, Xuelian ^[2]; Pattathil, Sivakumar ^[3]; da Costa Sousa, Leonardo ^[4]; Hahn, Michael G. ^[5]; Dale, Bruce ^[4]; Xu, Yong ^[3]; Balan, Venkatesh ^[6]

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+ Show Author Affiliations

1. Recep Tayyip Erdogan Univ., Rize (Turkey); Complex Carbohydrate Research Center, Athens, GA (United States)
2. Complex Carbohydrate Research Center, Athens, GA (United States); Mascoma LLC, Lebanon, PA (United States)
3. Nanjing Forestry Univ. (China); Jiangsu Province Key Lab. of Green Biomass-Based Fuels and Chemicals, Nanjing (China)
4. Michigan State Univ., East Lansing, MI (United States)
5. Complex Carbohydrate Research Center, Athens, GA (United States)
6. Univ. of Houston, TX (United States)

Publication Date:

2019-09-16

Research Org.:

Univ. of Wisconsin, Madison, WI (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

OSTI Identifier:

1609252

Grant/Contract Number:  

FC02-07ER64494; AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Frontiers in Energy Research

Additional Journal Information:

Journal Volume: 7; Journal ID: ISSN 2296-598X

Publisher:

Frontiers Research Foundation

Country of Publication:

United States

Language:

English

Subject:

59 BASIC BIOLOGICAL SCIENCES; 09 BIOMASS FUELS; Energy & Fuels