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

ABSTRACT 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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Available from: Noppadon Sathitsuksanoh, Sep 27, 2015
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    • "Fierobe et al. (2002) concluded that the accessibility of cellulase enzymes to cellulose is more important than the crystallinity index in determining the hydrolysis rate of several biomasses. The cellulose accessibility to the substrate increases when augmenting severity conditions of the pretreatments and the consequent increase in specific surface area (Rollin et al., 2010) or in pore size distribution (Grethlein, 1985) of the resulting solids. "
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    ABSTRACT: Olive stones (OS) are an abundant industrial by-product in countries of the Mediterranean Basin. In this work, olive stones were pretreated with hot water (autohydrolysis) at temperatures ranging from 150ºC to 225ºC for 0–600 s, and results were analyzed by using the severity factor (log R0). A log R0 value equal to 3.7 guaranteed the total solubilization of hemicelluloses, largely preserving cellulose and lignin in solid residue. In the prehydrolyzate, high oligosaccharide yield (14.7 kg/100 kg OS) and low acetic acid yield (0.24 kg/100 kg OS) were achieved at 190ºC and 300 s (log R0 = 3.59). The solid residues were hydrolyzed by cellulases to assess the enzymatic digestibility. Results showed that enzymatic saccharification of pre-treated solids at 225ºC for 600 s resulted in D-glucose yield of 54.3% (12.6 kg/100 kg OS), which improved 28-fold the yield obtained by using solids pretreated at 150ºC for 600 s. Mercury porosimetry illustrated that this increase could be explained by changes in average pore diameters rather than by changes in specific surface areas. The results demonstrated that olive stones are a potential raw material for the production of fermentable sugars. In the best operating conditions tested, autohydrolysis and subsequent enzymatic process have allowed the achievement of very high yields in oligosaccharides and d-glucose, respectively. Considering the autohydrolysis and enzymatic process, the total production of fermentable sugars leads to a total yield of 27.3 kg/100 kg OS.
    Industrial Crops and Products 08/2015; 70:100-106. DOI:10.1016/j.indcrop.2015.03.011 · 2.84 Impact Factor
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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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    ABSTRACT: The aim of this study is to evaluate the effect of the lignin content in four hybrid poplars for enhancing ethanol production. The study was conducted using steam explosion at 200 and 220°C for 5 min as a pre-treatment and then a simultaneous saccharification and fermentation (SSF) process with Saccharomyces cerevisiae. The composition of raw material, liquid and solid fraction obtained after pretreatment, enzymatic digestion, and ethanol production under the different experimental conditions were analyzed. The best results for bioethanol production were obtained from steam explosion pre-treatment carried out at 220°C with the hybrid poplar H-29, with cellulose recovery of over 63%, enzymatic hydrolysis yield of approximately 67%, and SSF yield of 70% of the theoretical value. However, the highest enzymatic hydrolysis yield (79%) was obtained for the hybrid poplar H-34, which has the lowest lignin content.
    International Journal of Green Energy 02/2015; DOI:10.1080/15435075.2014.887569 · 1.22 Impact Factor
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    • "Enzyme adsorption onto the substrate is the primary step in enzymatic degradation of cellulose [9,51]. Cellulose accessibility to enzyme has long been recognized as an essential factor controlling enzymatic hydrolysis of cellulosic biomass [52-54], and enzymatic hydrolysis rates and yields are often claimed to be related to enzyme adsorption [42,52,53,55,56]. Adsorption parameters calculated for the Langmuir model, the maximum adsorption capacity σ and equilibrium constant Kd, are summarized in Table 3. "
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    ABSTRACT: Background Pretreatment is essential to realize high product yields from biological conversion of naturally recalcitrant cellulosic biomass, with thermochemical pretreatments often favored for cost and performance. In this study, enzymatic digestion of solids from dilute sulfuric acid (DA), ammonia fiber expansion (AFEX™), and ionic liquid (IL) thermochemical pretreatments of corn stover were followed over time for the same range of total enzyme protein loadings to provide comparative data on glucose and xylose yields of monomers and oligomers from the pretreated solids. The composition of pretreated solids and enzyme adsorption on each substrate were also measured to determine. The extent glucose release could be related to these features. Results Corn stover solids from pretreatment by DA, AFEX, and IL were enzymatically digested over a range of low to moderate loadings of commercial cellulase, xylanase, and pectinase enzyme mixtures, the proportions of which had been previously optimized for each pretreatment. Avicel® cellulose, regenerated amorphous cellulose (RAC), and beechwood xylan were also subjected to enzymatic hydrolysis as controls. Yields of glucose and xylose and their oligomers were followed for times up to 120 hours, and enzyme adsorption was measured. IL pretreated corn stover displayed the highest initial glucose yields at all enzyme loadings and the highest final yield for a low enzyme loading of 3 mg protein/g glucan in the raw material. However, increasing the enzyme loading to 12 mg/g glucan or more resulted in DA pretreated corn stover attaining the highest longer-term glucose yields. Hydrolyzate from AFEX pretreated corn stover had the highest proportion of xylooligomers, while IL produced the most glucooligomers. However, the amounts of both oligomers dropped with increasing enzyme loadings and hydrolysis times. IL pretreated corn stover had the highest enzyme adsorption capacity. Conclusions Initial hydrolysis yields were highest for substrates with greater lignin removal, a greater degree of change in cellulose crystallinity, and high enzyme accessibility. Final glucose yields could not be clearly related to concentrations of xylooligomers released from xylan during hydrolysis. Overall, none of these factors could completely account for differences in enzymatic digestion performance of solids produced by AFEX, DA, and IL pretreatments.
    Biotechnology for Biofuels 05/2014; 7(1):71. DOI:10.1186/1754-6834-7-71 · 6.04 Impact Factor
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