Abstract
To investigate the interactions between acid pretreated grass lignin and cellobiohydrolase, three different lignin fractions were isolated from dilute acid pretreated switchgrass by (i) ethanol extraction, followed by (ii) dioxane/H2O extraction, and (iii) cellulase treatment, respectively. Structural properties of each lignin fraction were elucidated by GPC, 13C-NMR and 2D-HSQC NMR analyses. The adsorptions of cellobiohydrolase to the isolated lignin fractions were also studied by Langmuir adsorption isotherms. Ethanol-extractable lignin fraction, mainly composed of syringyl (S) and guaiacyl (G) units, had the lowest molecular weight, while dioxane/H2O-extractable lignin fraction had the lowest S/G ratio with higher content of p-coumaric acid (pCA) unit. The residual lignin fraction after enzymatic treatment had the highest S/G ratio without hydroxyphenyl (H) unit. Strong associations were found between lignin properties such as lignin composition and S/G ratio and its non-productive enzyme adsorption factors including the maximum adsorption capacity and binding strength.
Highlights
Rapid population growth and energy security concerns associated with fossil fuels have led to the development in alternative energy resources like biofuels (Cao et al, 2012)
Molecular weights of these lignins were lower than the values of untreated switchgrass in the previous study [5,000 g/mol of weight average molecular weight (Mw) and 2,940 g/mol of number average molecular weight (Mn), respectively] (Samuel et al, 2010)
The weight average molecular weight of the NO.1 lignin extracted by ethanol was 2,277 g/mol, which represents the lowest molecular weight among all three fractions, while the NO.2 and NO.3 lignin fractions had higher Mw (3,551 and 3,284 g/mol, respectively)
Summary
Rapid population growth and energy security concerns associated with fossil fuels have led to the development in alternative energy resources like biofuels (Cao et al, 2012). The adsorption of enzymes onto isolated lignins from dilute acid or hot water pretreated biomass has been studied (Zheng et al, 2013; Yu et al, 2014; Li et al, 2016; Lu et al, 2016; Sun et al, 2016). In order to fractionate lignin with various properties that might affect its adsorption capabilities to enzymes, in this study, three different lignin fractions were separated from the dilute acid pretreated switchgrass using ethanol extraction (Fraction NO. lignin), followed by 96% dioxane extraction (Fraction NO. lignin), and overloading with cellulase to recover lignin residue (Fraction NO. lignin). The relative quantity of each lignin fraction was 62.6, 35.4, and 2.0%
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