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Evaluating lignocellulosic biomass, its derivatives, and downstream products with Raman spectroscopy.

Lupoi JS, Gjersing E, Davis MF - Front Bioeng Biotechnol (2015)

Bottom Line: Hydrolysis and fermentation products, such as glucose and ethanol, can be quantified off-, at-, or on-line.Raman imaging has enabled researchers to develop a visual understanding of reactions, such as different pretreatment strategies, in real-time, while also providing integral chemical information.This review provides an overview of what Raman spectroscopy is, and how it has been applied to the analysis of whole lignocellulosic biomass, its derivatives, and downstream process monitoring.

View Article: PubMed Central - PubMed

Affiliation: Oak Ridge National Laboratory, BioEnergy Science Center , Oak Ridge, TN , USA ; National Renewable Energy Laboratory, National Bioenergy Center , Golden, CO , USA.

ABSTRACT
The creation of fuels, chemicals, and materials from plants can aid in replacing products fabricated from non-renewable energy sources. Before using biomass in downstream applications, it must be characterized to assess chemical traits, such as cellulose, lignin, or lignin monomer content, or the sugars released following an acid or enzymatic hydrolysis. The measurement of these traits allows researchers to gage the recalcitrance of the plants and develop efficient deconstruction strategies to maximize yields. Standard methods for assessing biomass phenotypes often have experimental protocols that limit their use for screening sizeable numbers of plant species. Raman spectroscopy, a non-destructive, non-invasive vibrational spectroscopy technique, is capable of providing qualitative, structural information and quantitative measurements. Applications of Raman spectroscopy have aided in alleviating the constraints of standard methods by coupling spectral data with multivariate analysis to construct models capable of predicting analytes. Hydrolysis and fermentation products, such as glucose and ethanol, can be quantified off-, at-, or on-line. Raman imaging has enabled researchers to develop a visual understanding of reactions, such as different pretreatment strategies, in real-time, while also providing integral chemical information. This review provides an overview of what Raman spectroscopy is, and how it has been applied to the analysis of whole lignocellulosic biomass, its derivatives, and downstream process monitoring.

No MeSH data available.


Related in: MedlinePlus

Raman mapping of tracheids during an ionic liquid pretreatment. (A) Bright-field microscopy images; (B) lignin maps (black boxes are the locations of cell corners); and (C) cellulose maps generated over 0–3 h of pretreatment [reprinted with permission from the Royal Society of Chemistry, Sun et al. (2013)].
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Figure 6: Raman mapping of tracheids during an ionic liquid pretreatment. (A) Bright-field microscopy images; (B) lignin maps (black boxes are the locations of cell corners); and (C) cellulose maps generated over 0–3 h of pretreatment [reprinted with permission from the Royal Society of Chemistry, Sun et al. (2013)].

Mentions: Raman microspectroscopy has been used to evaluate how a room temperature pretreatment with the ionic liquid (IL) 1-n-ethyl-3-methylimidazolium acetate modified the cell walls of poplar (Lucas et al., 2011). A 785 nm diode laser was used to collect spectral data from 50 μm poplar sections. Raman spectra from untreated poplar revealed the characteristic vibrational modes from cellulose, hemicellulose, and lignin. When the wood was swollen with water, the same peaks were identified; however, the intensities differed from the untreated samples. The intensity ratio of the 1460 cm−1 cellulose peak to the 1605 cm−1 lignin peak decreased, which signified diminutions in the cellulose-abundant S2 sub-layer compared to the hydrophobic, lignin-rich compound middle lamella (CML) region. The authors conclude that the swelling must be pushing the fibers apart, and progressing into more amorphous cellulose regions since crystalline cellulose fibers are recalcitrant to water penetration. The Raman spectra of the IL treated poplar samples depicted strong signals from the IL itself. When the samples were washed with water prior to analysis, the spectra showed no traces of IL vibrational modes, and resembled the water-swollen poplar Raman spectrum, leading to the conclusion that both the water and IL treatments led to similar overall cell wall compositions. Confocal Raman spectroscopy using a 785 nm diode laser enabled an evaluation of tissue-specific changes when pretreating corn stover with the IL 1-ethyl-3-methylimidazolium acetate (Sun et al., 2013). A temporal study was conducted to gage the lignin and cellulose remaining in the plant cell walls during the IL pretreatment at 120°C using 0, 30 min, 1, 2, and 3-h time points. To assess the changes brought about by the IL treatment, tracheids, sclerenchyma, and parenchyma cell structures were probed (see Figures 6 and 7). Before pretreating the corn stover, cellulose and lignin concentrations were highest in the cell corners (CCs) and CML portions of the three cell structures and in the secondary walls of the sclerenchyma and parenchyma cell types. The lignin content was measured to decrease rapidly during the IL treatment, while no preferential cellulose dissolution was detected. The IL pretreatment is known to cause swelling of the secondary wall, but not of the CML. Accordingly, more significant swelling was observed in tracheid and sclerenchyma cells than parenchyma cells, which are composed of primary cell walls. Although tracheids contained higher lignin concentrations and thicker walls than parenchyma cells, the lignin dissolution occurred more rapidly in the tracheid cells. Confocal Raman microscopy was also employed to evaluate normal and tension wood sections from poplar (Gierlinger and Schwanninger, 2006). The allocation of cell wall components was calculated following the integration of distinct vibrational modes. The Raman images of normal wood illustrated higher lignin concentrations in the CCs and the CML, and increased cellulose content in the S2 layer of parenchyma ray cells and two lesser layers located on each side of the CML, presumed to be S1. A higher fluorescence background was measured for CCs and the CML, which is expected due to the greater lignin concentrations in these regions. Analysis of tension wood samples revealed lignin to be localized in CCs and the CML, while no lignin was detected in the gelatinous, or G-layer. Signals from lignin increased, however, in the lumen. Aromatic compounds were measured to coalesce along an inner region of the G-layer, and were also found deeper in the G-layer, toward the CCs of the S2 layer.


Evaluating lignocellulosic biomass, its derivatives, and downstream products with Raman spectroscopy.

Lupoi JS, Gjersing E, Davis MF - Front Bioeng Biotechnol (2015)

Raman mapping of tracheids during an ionic liquid pretreatment. (A) Bright-field microscopy images; (B) lignin maps (black boxes are the locations of cell corners); and (C) cellulose maps generated over 0–3 h of pretreatment [reprinted with permission from the Royal Society of Chemistry, Sun et al. (2013)].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4403602&req=5

Figure 6: Raman mapping of tracheids during an ionic liquid pretreatment. (A) Bright-field microscopy images; (B) lignin maps (black boxes are the locations of cell corners); and (C) cellulose maps generated over 0–3 h of pretreatment [reprinted with permission from the Royal Society of Chemistry, Sun et al. (2013)].
Mentions: Raman microspectroscopy has been used to evaluate how a room temperature pretreatment with the ionic liquid (IL) 1-n-ethyl-3-methylimidazolium acetate modified the cell walls of poplar (Lucas et al., 2011). A 785 nm diode laser was used to collect spectral data from 50 μm poplar sections. Raman spectra from untreated poplar revealed the characteristic vibrational modes from cellulose, hemicellulose, and lignin. When the wood was swollen with water, the same peaks were identified; however, the intensities differed from the untreated samples. The intensity ratio of the 1460 cm−1 cellulose peak to the 1605 cm−1 lignin peak decreased, which signified diminutions in the cellulose-abundant S2 sub-layer compared to the hydrophobic, lignin-rich compound middle lamella (CML) region. The authors conclude that the swelling must be pushing the fibers apart, and progressing into more amorphous cellulose regions since crystalline cellulose fibers are recalcitrant to water penetration. The Raman spectra of the IL treated poplar samples depicted strong signals from the IL itself. When the samples were washed with water prior to analysis, the spectra showed no traces of IL vibrational modes, and resembled the water-swollen poplar Raman spectrum, leading to the conclusion that both the water and IL treatments led to similar overall cell wall compositions. Confocal Raman spectroscopy using a 785 nm diode laser enabled an evaluation of tissue-specific changes when pretreating corn stover with the IL 1-ethyl-3-methylimidazolium acetate (Sun et al., 2013). A temporal study was conducted to gage the lignin and cellulose remaining in the plant cell walls during the IL pretreatment at 120°C using 0, 30 min, 1, 2, and 3-h time points. To assess the changes brought about by the IL treatment, tracheids, sclerenchyma, and parenchyma cell structures were probed (see Figures 6 and 7). Before pretreating the corn stover, cellulose and lignin concentrations were highest in the cell corners (CCs) and CML portions of the three cell structures and in the secondary walls of the sclerenchyma and parenchyma cell types. The lignin content was measured to decrease rapidly during the IL treatment, while no preferential cellulose dissolution was detected. The IL pretreatment is known to cause swelling of the secondary wall, but not of the CML. Accordingly, more significant swelling was observed in tracheid and sclerenchyma cells than parenchyma cells, which are composed of primary cell walls. Although tracheids contained higher lignin concentrations and thicker walls than parenchyma cells, the lignin dissolution occurred more rapidly in the tracheid cells. Confocal Raman microscopy was also employed to evaluate normal and tension wood sections from poplar (Gierlinger and Schwanninger, 2006). The allocation of cell wall components was calculated following the integration of distinct vibrational modes. The Raman images of normal wood illustrated higher lignin concentrations in the CCs and the CML, and increased cellulose content in the S2 layer of parenchyma ray cells and two lesser layers located on each side of the CML, presumed to be S1. A higher fluorescence background was measured for CCs and the CML, which is expected due to the greater lignin concentrations in these regions. Analysis of tension wood samples revealed lignin to be localized in CCs and the CML, while no lignin was detected in the gelatinous, or G-layer. Signals from lignin increased, however, in the lumen. Aromatic compounds were measured to coalesce along an inner region of the G-layer, and were also found deeper in the G-layer, toward the CCs of the S2 layer.

Bottom Line: Hydrolysis and fermentation products, such as glucose and ethanol, can be quantified off-, at-, or on-line.Raman imaging has enabled researchers to develop a visual understanding of reactions, such as different pretreatment strategies, in real-time, while also providing integral chemical information.This review provides an overview of what Raman spectroscopy is, and how it has been applied to the analysis of whole lignocellulosic biomass, its derivatives, and downstream process monitoring.

View Article: PubMed Central - PubMed

Affiliation: Oak Ridge National Laboratory, BioEnergy Science Center , Oak Ridge, TN , USA ; National Renewable Energy Laboratory, National Bioenergy Center , Golden, CO , USA.

ABSTRACT
The creation of fuels, chemicals, and materials from plants can aid in replacing products fabricated from non-renewable energy sources. Before using biomass in downstream applications, it must be characterized to assess chemical traits, such as cellulose, lignin, or lignin monomer content, or the sugars released following an acid or enzymatic hydrolysis. The measurement of these traits allows researchers to gage the recalcitrance of the plants and develop efficient deconstruction strategies to maximize yields. Standard methods for assessing biomass phenotypes often have experimental protocols that limit their use for screening sizeable numbers of plant species. Raman spectroscopy, a non-destructive, non-invasive vibrational spectroscopy technique, is capable of providing qualitative, structural information and quantitative measurements. Applications of Raman spectroscopy have aided in alleviating the constraints of standard methods by coupling spectral data with multivariate analysis to construct models capable of predicting analytes. Hydrolysis and fermentation products, such as glucose and ethanol, can be quantified off-, at-, or on-line. Raman imaging has enabled researchers to develop a visual understanding of reactions, such as different pretreatment strategies, in real-time, while also providing integral chemical information. This review provides an overview of what Raman spectroscopy is, and how it has been applied to the analysis of whole lignocellulosic biomass, its derivatives, and downstream process monitoring.

No MeSH data available.


Related in: MedlinePlus