Increasing Cellulose Accessibility Is More Important Than Removing Lignin: A Comparison of Cellulose Solvent-Based Lignocellulose Fractionation and Soaking in Aqueous Ammonia

Biological Systems Engineering Department, Virginia Polytechnic Institute and State University, 210-A Seitz Hall, Blacksburg, Virginia 24061, USA.
Biotechnology and Bioengineering (Impact Factor: 4.13). 01/2011; 108(1):22-30. DOI: 10.1002/bit.22919
Source: PubMed


While many pretreatments attempt to improve the enzymatic digestibility of biomass by removing lignin, this study shows that improving the surface area accessible to cellulase is a more important factor for achieving a high sugar yield. Here we compared the pretreatment of switchgrass by two methods, cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) and soaking in aqueous ammonia (SAA). Following pretreatment, enzymatic hydrolysis was conducted at two cellulase loadings, 15 filter paper units (FPU)/g glucan and 3 FPU/g glucan, with and without BSA blocking of lignin absorption sites. The hydrolysis results showed that the lignin remaining after SAA had a significant negative effect on cellulase performance, despite the high level of delignification achieved with this pretreatment. No negative effect due to lignin was detected for COSLIF-treated substrate. SEM micrographs, XRD crystallinity measurements, and cellulose accessibility to cellulase (CAC) determinations confirmed that COSLIF fully disrupted the cell wall structure, resulting in a 16-fold increase in CAC, while SAA caused a 1.4-fold CAC increase. A surface plot relating the lignin removal, CAC, and digestibility of numerous samples (both pure cellulosic substrates and lignocellulosic materials pretreated by several methods) was also developed to better understand the relative impacts of delignification and CAC on glucan digestibility.

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    • "The results obtained from the two hydrolysis methods deviated for 60 wt% TBPH treatment. Rollin et al. (2011) demonstrated that improving cellulose accessibility is more beneficial for the enzymatic digestibility of lignocellulosic biomass than lignin removal. "
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    • "Mansfield, Mooney, and Saddler (1999) reported that lignin content between 20 and 30% of lignocellulosic biomass is the major barrier to enzymatic saccharification. On the other hand, Downloaded by [Universidad Autonoma Metropolitana] at 16:27 24 March 2015 in a recent work Rollin et al. (2011) concluded that increasing cellulose accessibility was a more important pretreatment consideration than delignification for effectively releasing sugars from recalcitrant lignocellulose at high yield. Lignins are large, complex polymers of three principal alcohols: coniferyl, sinapyl, and p-coumaryl (Amthor 2003). "
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