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Visualization of Miscanthus × giganteus cell wall deconstruction subjected to dilute acid pretreatment for enhanced enzymatic digestibility.

Ji Z, Zhang X, Ling Z, Zhou X, Ramaswamy S, Xu F - Biotechnol Biofuels (2015)

Bottom Line: DAP of M. × giganteus resulted in solubilization of arabinoxylan and cross-linking hydroxycinnamic acids in a temperature-dependent manner.The optimized pretreatment (1% H2SO4, 170°C for 30 min) resulted in significant enhancement in the saccharification efficiency (51.20%) of treated samples in 72 h, which amounted to 4.4-fold increase in sugar yield over untreated samples (11.80%).The consequently occurred changes in inner cell wall structure including damaging, increase of porosity and loss of mechanical resistance were also found to enhance enzyme access to cellulose and further sugar yield.

View Article: PubMed Central - PubMed

Affiliation: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China ; Ministry of Education Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Tsinghua East Road, Beijing, 100083 China.

ABSTRACT

Background: The natural recalcitrance of lignocellulosic plant cell walls resulting from complex arrangement and distribution of heterogeneous components impedes deconstruction of such cell walls. Dilute acid pretreatment (DAP) is an attractive method to overcome the recalcitrant barriers for rendering enzymatic conversion of polysaccharides. In this study, the internodes of Miscanthus × giganteus, a model bioenergy crop, were subjected to DAP to yield a range of samples with altered cell wall structure and chemistry. The consequent morphological and compositional changes and their possible impact on saccharification efficiency were comprehensively investigated. The use of a series of microscopic and microspectroscopic techniques including fluorescence microscopy (FM), transmission electron microscopy (TEM) and confocal Raman microscopy (CRM)) enabled correlative cell wall structural and chemical information to be obtained.

Results: DAP of M. × giganteus resulted in solubilization of arabinoxylan and cross-linking hydroxycinnamic acids in a temperature-dependent manner. The optimized pretreatment (1% H2SO4, 170°C for 30 min) resulted in significant enhancement in the saccharification efficiency (51.20%) of treated samples in 72 h, which amounted to 4.4-fold increase in sugar yield over untreated samples (11.80%). The remarkable improvement could be correlated to a sequence of changes occurring in plant cell walls due to their pretreatment-induced deconstruction, namely, loss in the matrix between neighboring cell walls, selective removal of hemicelluloses, redistribution of phenolic polymers and increased exposure of cellulose. The consequently occurred changes in inner cell wall structure including damaging, increase of porosity and loss of mechanical resistance were also found to enhance enzyme access to cellulose and further sugar yield.

Conclusions: DAP is a highly effective process for improving bioconversion of cellulose to glucose by breaking down the rigidity and resistance of cell walls. The combination of the most relevant microscopic and microanalytical techniques employed in this work provided information crucial for evaluating the influence of anatomical and compositional changes on enhanced enzymatic digestibility.

No MeSH data available.


Related in: MedlinePlus

Raman images of cellulose distribution within M. × giganteus cell walls upon dilute acid pretreatment. a Untreated; b pretreated M. × giganteus at 160°C, 0.5% H2SO4 for 15 min; c pretreated M. × giganteus at 170°C, 1% H2SO4 for 30 min. Sf sclerenchyma fibers; Par parenchyma, Pxv protoxylem vessel, Mxv metaxylem vessel, St sieve tube, Com companion cell.
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Fig9: Raman images of cellulose distribution within M. × giganteus cell walls upon dilute acid pretreatment. a Untreated; b pretreated M. × giganteus at 160°C, 0.5% H2SO4 for 15 min; c pretreated M. × giganteus at 170°C, 1% H2SO4 for 30 min. Sf sclerenchyma fibers; Par parenchyma, Pxv protoxylem vessel, Mxv metaxylem vessel, St sieve tube, Com companion cell.

Mentions: Cellulose distribution in the M. × giganteus was highlighted by integrating over the spectral range from 2,789 to 2,932 cm−1. The Sf of native materials with high brightness suggested accumulation of celluloses in these regions, contrary to Pxv and Mxv (Figure 9a). Though the 2,886 cm−1 band is admittedly favored from hemicelluloses, evaluation of Raman spectra of treated samples yet revealed an increase in this peak with diminution of hemicelluloses (Figure 4). The Raman imaging data also confirmed the results. Compared to Figure 9b, the cellulose concentration in samples treated with anabatic severity increased significantly, typically in the Sf (Figure 9c), which implies greater exposure of cellulose. Phenolics and hemicelluloses are known to coat cellulose microfibrils hindering chemical deconstruction of lignocellulosic cell walls [56, 57]. Xylans irreversibly absorbed on cellulose surface further reduce the action of cellulases [58]. Therefore, with the removal of a large portion of phenolics and hemicelluloses, cellulose cores were more exposed to be detected. The exposure of cellulose greatly facilitates enzymatic hydrolysis of cellulosic fractions in the treated biomass. This further explained the higher yield of fermentable sugars as illustrated in Figure 2. Holopainen-Mantila et al. [14] also suggested a similar effect on wheat straw cell walls after hydrothermal pretreatment.Figure 9


Visualization of Miscanthus × giganteus cell wall deconstruction subjected to dilute acid pretreatment for enhanced enzymatic digestibility.

Ji Z, Zhang X, Ling Z, Zhou X, Ramaswamy S, Xu F - Biotechnol Biofuels (2015)

Raman images of cellulose distribution within M. × giganteus cell walls upon dilute acid pretreatment. a Untreated; b pretreated M. × giganteus at 160°C, 0.5% H2SO4 for 15 min; c pretreated M. × giganteus at 170°C, 1% H2SO4 for 30 min. Sf sclerenchyma fibers; Par parenchyma, Pxv protoxylem vessel, Mxv metaxylem vessel, St sieve tube, Com companion cell.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4513789&req=5

Fig9: Raman images of cellulose distribution within M. × giganteus cell walls upon dilute acid pretreatment. a Untreated; b pretreated M. × giganteus at 160°C, 0.5% H2SO4 for 15 min; c pretreated M. × giganteus at 170°C, 1% H2SO4 for 30 min. Sf sclerenchyma fibers; Par parenchyma, Pxv protoxylem vessel, Mxv metaxylem vessel, St sieve tube, Com companion cell.
Mentions: Cellulose distribution in the M. × giganteus was highlighted by integrating over the spectral range from 2,789 to 2,932 cm−1. The Sf of native materials with high brightness suggested accumulation of celluloses in these regions, contrary to Pxv and Mxv (Figure 9a). Though the 2,886 cm−1 band is admittedly favored from hemicelluloses, evaluation of Raman spectra of treated samples yet revealed an increase in this peak with diminution of hemicelluloses (Figure 4). The Raman imaging data also confirmed the results. Compared to Figure 9b, the cellulose concentration in samples treated with anabatic severity increased significantly, typically in the Sf (Figure 9c), which implies greater exposure of cellulose. Phenolics and hemicelluloses are known to coat cellulose microfibrils hindering chemical deconstruction of lignocellulosic cell walls [56, 57]. Xylans irreversibly absorbed on cellulose surface further reduce the action of cellulases [58]. Therefore, with the removal of a large portion of phenolics and hemicelluloses, cellulose cores were more exposed to be detected. The exposure of cellulose greatly facilitates enzymatic hydrolysis of cellulosic fractions in the treated biomass. This further explained the higher yield of fermentable sugars as illustrated in Figure 2. Holopainen-Mantila et al. [14] also suggested a similar effect on wheat straw cell walls after hydrothermal pretreatment.Figure 9

Bottom Line: DAP of M. × giganteus resulted in solubilization of arabinoxylan and cross-linking hydroxycinnamic acids in a temperature-dependent manner.The optimized pretreatment (1% H2SO4, 170°C for 30 min) resulted in significant enhancement in the saccharification efficiency (51.20%) of treated samples in 72 h, which amounted to 4.4-fold increase in sugar yield over untreated samples (11.80%).The consequently occurred changes in inner cell wall structure including damaging, increase of porosity and loss of mechanical resistance were also found to enhance enzyme access to cellulose and further sugar yield.

View Article: PubMed Central - PubMed

Affiliation: Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, 100083 China ; Ministry of Education Key Laboratory of Wooden Material Science and Application, Beijing Forestry University, Tsinghua East Road, Beijing, 100083 China.

ABSTRACT

Background: The natural recalcitrance of lignocellulosic plant cell walls resulting from complex arrangement and distribution of heterogeneous components impedes deconstruction of such cell walls. Dilute acid pretreatment (DAP) is an attractive method to overcome the recalcitrant barriers for rendering enzymatic conversion of polysaccharides. In this study, the internodes of Miscanthus × giganteus, a model bioenergy crop, were subjected to DAP to yield a range of samples with altered cell wall structure and chemistry. The consequent morphological and compositional changes and their possible impact on saccharification efficiency were comprehensively investigated. The use of a series of microscopic and microspectroscopic techniques including fluorescence microscopy (FM), transmission electron microscopy (TEM) and confocal Raman microscopy (CRM)) enabled correlative cell wall structural and chemical information to be obtained.

Results: DAP of M. × giganteus resulted in solubilization of arabinoxylan and cross-linking hydroxycinnamic acids in a temperature-dependent manner. The optimized pretreatment (1% H2SO4, 170°C for 30 min) resulted in significant enhancement in the saccharification efficiency (51.20%) of treated samples in 72 h, which amounted to 4.4-fold increase in sugar yield over untreated samples (11.80%). The remarkable improvement could be correlated to a sequence of changes occurring in plant cell walls due to their pretreatment-induced deconstruction, namely, loss in the matrix between neighboring cell walls, selective removal of hemicelluloses, redistribution of phenolic polymers and increased exposure of cellulose. The consequently occurred changes in inner cell wall structure including damaging, increase of porosity and loss of mechanical resistance were also found to enhance enzyme access to cellulose and further sugar yield.

Conclusions: DAP is a highly effective process for improving bioconversion of cellulose to glucose by breaking down the rigidity and resistance of cell walls. The combination of the most relevant microscopic and microanalytical techniques employed in this work provided information crucial for evaluating the influence of anatomical and compositional changes on enhanced enzymatic digestibility.

No MeSH data available.


Related in: MedlinePlus