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United States Department of Agriculture

Agricultural Research Service

Research Project: Bioproducts from Agricultural Feedstocks

Location: Bioproduct Chemistry and Engineering Research

Title: Chemical structures of corn stover and its residue after dilute acid prehydrolysis and enzymatic hydrolysis: Insight into factors limiting enzymatic hydrolysis

Authors
item Mao, J.D. -
item Holtman, Kevin
item Franqui-Villanueva, Diana

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 2010
Publication Date: November 24, 2010
Citation: Mao, J., Holtman, K.M., Franquivillanueva, D.M. 2010. Chemical structures of corn stover and its residue after dilute acid prehydrolysis and enzymatic hydrolysis: Insight into factors limiting enzymatic hydrolysis. Journal of Agricultural and Food Chemistry. 58(22):11680-11687.

Interpretive Summary: Corn stover, the residue left over after corn harvest, is potentially a viatal source of feedstock for the biofuels industry provided it can be pretreated to release its useful sugars. A study was undertaken to understand the effect of dilute acid prehydrolysis (DAP) and enzymatic hydrolysis (RES) on corn stover to provide evidence for the limitations to the effectiveness of enzyme hydrolysis. Specific advanced characterization techniques (advanced solid-state NMR spectral-editing techniques as well as 1H-13C two-dimensional NMR) were employed showing that dilute acid prehydrolysis was important for pretreatment and that it left behind cinnamic acid links in the biomass. This result was different from acid pretreatment of a purified cellulose that had been reported in the literature suggesting that acid pretreatment may modify the structure of purified cellulose more than “real-life” biomass, which is more complex than pure cellulose. Therefore biomass may be a better substrate than model biopolymers and compounds for assessing industrial processing techniques.

Technical Abstract: Advanced solid-state NMR techniques and wet chemical analyses were applied to investigate untreated corn stover (UCS) and its residues after dilute acid prehydrolysis (DAP) and enzymatic hydrolysis (RES) to provide evidence for the limitations to the effectiveness of enzyme hydrolysis. Advanced solid-state NMR spectral-editing techniques as well as 1H-13C two-dimensional heteronuclear correlation NMR (2D HETCOR) were employed. Our results indicated that dilute acid prehydrolysis selectively removed amorphous carbohydrates, increased aromatic CH/other protonated -CC- and enriched alkyl CH and CH2 components. Cinnamic acids were increased, and proteinaceous materials and N-containing degradation or condensation compounds were absorbed or coprecipitated in RES. 2D HETCOR experiments indicated a close association between lignin and the residual carbohydrates. Ketones/aldehydes were not detected in the DAP, in contrast to a report in which an appreciable amount of ketones/aldehydes was generated from the acid pretreatment of a purified cellulose in the literature. This suggested that acid pretreatment may modify the structure of purified cellulose more than biomass and that biomass may be a better substrate than model biopolymers and compounds for assessing structural changes that occur with industrial processing. On the basis of NMR and wet chemical analyses, we found the following factors could cause the limitations to the effectiveness of enzymatic hydrolysis: (1) chemical modification of carbohydrates limited the biologically degradable carbohydrates available; (2) cinnamic acids in the residue accumulated; (3) accessibility was potentially limited due to the close association of carbohydrates with lignin; and (4) proteinaceous materials and N-containing degradation or condensation compounds were absorbed or coprecipitated.

Last Modified: 9/22/2014
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