An open-source machine-learning approach for obtaining high-quality quantitative wood anatomy data from E. grandis and P. radiata xylem

Quantitative wood anatomy is a subfield in dendrochronology that requires effective open-source image analysis tools. In this research, the bioimage analysis software QuPath (v0.4.4) is introduced as a candidate for accurately quantifying the cellular properties of the xylem in an automated manner. Additionally, the potential of QuPath to detect the transition of early- to latewood tracheids over the growing season was evaluated to assess a potential application in dendroecological studies. Various algorithms in QuPath were optimized to quantify different xylem cell types in Eucalyptus grandis and the transition of early- to latewood tracheids in Pinus radiata. These algorithms were coded into cell detection scripts for automatic quantification of stem microsections and compared to a manually curated method to assess the accuracy of the cell detections. The automatic cell detection approach, using QuPath, has been validated to be reproducible with an acceptable error when assessing fibers, vessels, early- and latewood tracheids. However, further optimization for parenchyma is still required. This proposed method developed in QuPath provides a scalable and accurate approach for quantifying anatomical features in stem microsections. With minor amendments to the detection and classification algorithms, this strategy is likely to be viable in other plant species.

Structure investigation of light-colored lignin extracted by Lewis acid-based deep eutectic solvent from softwood

Lignin is the most abundant natural phenolic polymer. However, the severe condensations of industrial lignin resulted in an undesirable apparent morphology and darker color, which hindered its application in the field of daily chemicals. Therefore, a ternary deep eutectic solvent is used to obtain lignin with light-color and low condensations from softwood. The results showed that the brightness value of lignin extracted from aluminum chloride-1,4-butanediol-choline chloride at 100 °C and 1.0 h was 77.9, and the lignin yield was 32.2 ± 0.6%. It is important that 95.8% of β-O-4 linkages (β-O-4 and β-O-4') was retained. Lignin is used to prepare sunscreens and is added to physical sunscreens at 5%, with SPF up to 26.95 ± 4.20. Meanwhile, enzyme hydrolysis experiments and reaction liquid composition tests were also conducted. In conclusion, a systematic understanding of this efficient process could facilitate high-value utilization of lignocellulosic biomass in industrial processes.

Investigating the role of AA9 LPMOs in enzymatic hydrolysis of differentially steam-pretreated spruce

BACKGROUND

To realize the full potential of softwood-based forest biorefineries, the bottlenecks of enzymatic saccharification of softwood need to be better understood. Here, we investigated the potential of lytic polysaccharide monooxygenases (LPMO9s) in softwood saccharification. Norway spruce was steam-pretreated at three different severities, leading to varying hemicellulose retention, lignin condensation, and cellulose ultrastructure. Hydrolyzability of the three substrates was assessed after pretreatment and after an additional knife-milling step, comparing the efficiency of cellulolytic Celluclast + Novozym 188 and LPMO-containing Cellic CTec2 cocktails. The role of Thermoascus aurantiacus TaLPMO9 in saccharification was assessed through time-course analysis of sugar release and accumulation of oxidized sugars, as well as wide-angle X-ray scattering analysis of cellulose ultrastructural changes.

RESULTS

Glucose yield was 6% (w/w) with the mildest pretreatment (steam pretreatment at 210 °C without catalyst) and 66% (w/w) with the harshest (steam pretreatment at 210 °C with 3%(w/w) SO₂) when using Celluclast + Novozym 188. Surprisingly, the yield was lower with all substrates when Cellic CTec2 was used. Therefore, the conditions for optimal LPMO activity were tested and it was found that enough O₂ was present over the headspace and that the reducing power of the lignin of all three substrates was sufficient for the LPMOs in Cellic CTec2 to be active. Supplementation of Celluclast + Novozym 188 with TaLPMO9 increased the conversion of glucan by 1.6-fold and xylan by 1.5-fold, which was evident primarily in the later stages of saccharification (24-72 h). Improved glucan conversion could be explained by drastically reduced cellulose crystallinity of spruce substrates upon TaLPMO9 supplementation.

CONCLUSION

Our study demonstrated that LPMO addition to hydrolytic enzymes improves the release of glucose and xylose from steam-pretreated softwood substrates. Furthermore, softwood lignin provides enough reducing power for LPMOs, irrespective of pretreatment severity. These results provided new insights into the potential role of LPMOs in saccharification of industrially relevant softwood substrates.

The role of acetone-fractionated Kraft lignin molecular structure on surface adhesion to formaldehyde-based resins

One of the key strategies for valorizing kraft lignin (KL) into value-added products such as bio-based adhesives is to perform solvent fractionation of KL to produce lignin with improved homogeneity. Understanding the structure and properties of fractionated KL will aid in the selection of the best samples for certain applications. In this study, acetone-fractionated KL from softwood and hardwood was characterized to understand its chemical structure, elemental composition, molecular weight, and thermal properties. The results revealed that acetone-insoluble KL (AIKL) fractions from softwood and hardwood have greater molecular weight, polydispersity, glass temperature, carbohydrate content, aliphatic hydroxyl groups, and a variety of native wood lignin side chains. In contrast, acetone-soluble KL (ASKL) fractions have a significantly lower molecular weight and polydispersity, a lower glass-transition temperature, a more condensed structure, more aromatic hydroxyl groups, and fewer native wood lignin side chains. In addition, the ASKL samples demonstrated stronger adhesive force and work of adhesion toward phenol-formaldehyde (PF) and urea-formaldehyde (UF) resins than the AIKL samples, regardless of the lignin source. These findings suggest that ASKL has great potential as a substitute for phenol in PF resins and as a green additive to reinforce UF resins.

Non-destructive preservation state estimation of waterlogged archaeological wooden artifacts

Non-destructive preservation state estimation is an essential prerequisite for the preservation and conservation of waterlogged archaeological wooden artifacts. Herein, Near Infrared (NIR) spectroscopy coupled with orthogonal partial least squares discriminant analysis (OPLS-DA) were applied to assess sixty-four waterlogged archaeological woods collected from seven excavation sites in the period range of 2900 BCE-1912 CE, aiming at developing a non-destructive, accurate and rapid preservation state estimation methodology. The role of non-decayed recent wood of relevant species on preservation state estimation was studied in prior, showing the use of non-decayed recent wood could not improve the predictive ability. Besides, the high variability in terms of chemical structure between archaeological softwoods and archaeological hardwoods did affect the preservation state estimation. Thus, a simple OPLS-DA model of non-destructively distinguishing archaeological hardwoods from softwoods, R²X_cum of 0.659, R²Y_cum of 0.836 and Q²_cum of 0.763, was established to avoid and overcome destructive approach for wood identification. Then, the well-defined three grouped separations of slightly-decayed, moderately-decayed and severely-decayed waterlogged archaeological woods were revealed in OPLS-DA models, providing R²X_cum of 0.793, R²Y_cum of 0.738, Q²_cum of 0.680, and R²X_cum of 0.780, R²Y_cum of 0.901, Q²_cum of 0.870, for waterlogged archaeological hardwoods and waterlogged archaeological softwoods respectively. Potential predictive wood spectral bands were screened and tentatively identified as hydroxyls of crystalline cellulose, acetyl groups of hemicelluloses, C-H bands of lignin, which guaranteed the elimination of non-structural compounds, such as water and inorganic components interference. Furthermore, the developed NIR methodology was validated by an extensively used destructive method consisting of anatomical characteristics, maximum water content and basic density analyses. The results indicated that NIR coupled to chemometrics could non-destructively and accurately predict the preservation states of waterlogged archaeological wooden artifacts and avoid the interference of water and inorganic deposits.

Systems metabolic engineering upgrades Corynebacterium glutamicum to high-efficiency cis, cis-muconic acid production from lignin-based aromatics

Lignin displays a highly challenging renewable. To date, massive amounts of lignin, generated in lignocellulosic processing facilities, are for the most part merely burned due to lacking value-added alternatives. Aromatic lignin monomers of recognized relevance are in particular vanillin, and to a lesser extent vanillate, because they are accessible at high yield from softwood-lignin using industrially operated alkaline oxidative depolymerization. Here, we metabolically engineered C. glutamicum towards cis, cis-muconate (MA) production from these key aromatics. Starting from the previously created catechol-based producer C. glutamicum MA-2, systems metabolic engineering first discovered an unspecific aromatic aldehyde reductase that formed aromatic alcohols from vanillin, protocatechualdehyde, and p- hydroxybenzaldehyde, and was responsible for the conversion up to 57% of vanillin into vanillyl alcohol. The alcohol was not re-consumed by the microbe later, posing a strong drawback on the producer. The identification and subsequent elimination of the encoding fudC gene completely abolished vanillyl alcohol formation. Second, the initially weak flux through the native vanillin and vanillate metabolism was enhanced up to 2.9-fold by implementing synthetic pathway modules. Third, the most efficient protocatechuate decarboxylase AroY for conversion of the midstream pathway intermediate protocatechuate into catechol was identified out of several variants in native and codon optimized form and expressed together with the respective helper proteins. Fourth, the streamlined modules were all genomically combined which yielded the final strain MA-9. MA-9 produced bio-based MA from vanillin, vanillate, and seven structurally related aromatics at maximum selectivity. In addition, MA production from softwood-based vanillin, obtained through alkaline depolymerization, was demonstrated.

Critical comparison of the properties of cellulose nanofibers produced from softwood and hardwood through enzymatic, chemical and mechanical processes

Current knowledge on the properties of different types of cellulose nanofibers (CNFs) is fragmented. Properties variation is very extensive, depending on raw materials, effectiveness of the treatments to extract the cellulose fraction from the lignocellulosic biomass, pretreatments to facilitate cellulose fibrillation and final mechanical process to separate the microfibrils. Literature offers multiple parameters to characterize the CNFs prepared by different routes. However, there is a lack of an extensive guide to compare the CNFs. In this study, we perform a critical comparison of rheological, compositional, and morphological features of CNFs, produced from the most representative types of woody plants, hardwood and softwood, using different types and intensities of pretreatments, including enzymatic, chemical and mechanical ones, and varying the severity of mechanical treatment focusing on the relationship between macroscopic and microscopic parameters. This structured information will be exceedingly useful to select the most appropriate CNF for a certain application based on the most relevant parameters in each case.

Lignin valorization through efficient microbial production of β-ketoadipate from industrial black liquor

Vanillin and vanillate are the major lignin-derived aromatic compounds produced through the alkaline oxidation of softwood lignin. Because the production of higher-value added chemicals from these compounds is essential for lignin valorization, the microbial production of β-ketoadipate, a promising raw material for the synthesis of novel nylons, from lignin was considered. Pseudomonas putida KT2440 was engineered to convert vanillin and vanillate to β-ketoadipate. By examining the culture conditions with an initial culture volume of 1 L, the engineered strain completely converted 25 g of vanillin and 25 g of vanillate and produced approximately 23 g of β-ketoadipate from each of them with a yield of 93% or higher. Furthermore, this strain showed the ability to efficiently produce β-ketoadipate from softwood lignin extracts in black liquor, a byproduct of pulp production. These results suggest that the production of β-ketoadipate from industrial black liquor is highly feasible for substantial lignin valorization.

Facile preparation of all-cellulose composites from softwood, hardwood, and agricultural straw cellulose by a simple route of partial dissolution

In this study, we report a novel, facile, and green method that was used for creating a new all-cellulose composite (ACC) based on inorganic molten salt solvent. Three representatively native fibers from softwood (Pinus kesiya), hardwood (Eucalyptus globulus), and agricultural straw (Zea mays) were selected to verify the effect of the method. The welded sheets were thoroughly characterized and compared. Cellulose sheets from the pine exhibited excellent mechanical properties (σb 16.94 MPa) and thermal stability (T_max 265 °C) after the welding process, while the corn stalk sheets displayed more robust and thermostable features than the eucalyptus. The welding technique using inorganic metal salt hydrate provides a promising and convenient route to obtain firm sheet-materials with micro- or nano-structures from nature fibers.

Isolation of cellulose nanocrystals from different waste bio-mass collating their liquid crystal ordering with morphological exploration

Cellulose nanocrystals (CNCs) have been recognized as one of the most promising nanofillers in modern science and technology owing to their outstanding characteristics of renewability, biodegradability, excellent mechanical strength, and liquid crystalline behavior. Interestingly, these properties are dependent on their genetic and also on the isolation process. Therefore, this research aimed to unveil how the biological variations of cellulose can influence on the physical properties of the extracted CNCs. A standard optimized extraction process was adopted to isolate the CNCs from different sources. Extracted CNCs were compared through characterization tools, including Fourier Transformation Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetry Analysis (TGA), Dynamic Light Scattering (DLS), Field Emission Scanning Electron Microscopy (FE-SEM), Atomic Force Microscopy (AFM), and Polarized Optical Microscopy (POM). Different self-assembly patterns were observed for different CNCs, owing to their biological variations. The resultant nanocrystals displayed variable morphologies such as spherical, rod, and needle shape. The hydrodynamic diameter, crystallinity index, decomposition temperature, liquid crystallinity, and storage modulus were varied. Nanocrystals isolated from non-wood feedstock have shown a higher degree of polymerization of 108.2 and a high Crystllinity Index (C·I.) of 55.1%. The rod-like morphology with the liquid crystalline pattern was obtained at 3 wt% concentration for SCNC.

Quantifying the relative importance of major tracers for fine particles released from biofuel combustion in households in the rural North China Plain

Biomass burning tracers have been widely used to identify biomass burning types, but such tools can sometimes cause large uncertainties in the source attribution studies of PM_2.5 (particles with an aerodynamic diameter of smaller than 2.5 μm). To quantify the relative importance of the major biomass burning tracers in PM_2.5 released from biofuels combusted in the North China Plain, combustion experiments under the smoldering and flaming combustion conditions were conducted using nine types of typical household biofuels including two types of agricultural wastes, five types of hardwoods, one softwood, and one mixed wood briquette. PM_2.5 samples were collected from the combustion experiments and source profiles of PM_2.5 were thus determined for various biofuels under the two different combustion conditions. Carbonaceous species including organic carbon (OC) and elemental carbon (EC) were the major chemical components of the PM_2.5 released from combustion of all the tested biofuels, with mass fractions of 37-45% and 4-7% under the smoldering condition and 11-25% and 7-29% under the flaming condition, respectively. Higher mass fractions of water-soluble inorganic ions (WSIIs, e.g., K⁺ and Cl^-) in PM_2.5 were observed under the flaming than smoldering combustion condition, while anhydrosugars (levoglucosan (LG) and mannosan (MN)) presented in an opposite pattern. The average LG/MN ratio in PM_2.5 changed significantly with biofuel type (20-55 for agricultural wastes, 10-22 for hardwoods (except elm) and 3-6 for softwood), but varied little with combustion condition. In contrast, the K⁺/LG ratio in PM_2.5 varied significantly between smoldering (<0.2) and flaming (>0.6) combustion conditions for all the biofuel types except softwood. Results from this study suggested that the ratio LG/MN was the best tracer for identifying the biofuel types and the ratio K⁺/LG is suitable for identifying the combustion conditions in this region.

The key role of delignification in overcoming the inherent recalcitrance of Chinese fir for biorefining

The enzymatic digestibility of softwood is hindered for its highly recalcitrant nature to enzymatic attack. In this study, the effects of dilute sulfuric acid pretreatment (DSAP), acidic sodium chlorite pretreatment (SCP), and their combined pretreatments (DSA-SCP and SC-DSAP) on Chinese fir sawdust were investigated, respectively. Results demonstrated that lignin was the most important obstacle, and digestibility increased linearly with lignin removal yield. Furthermore, the results revealed that the order of sequential pretreatment significantly affected the delignification, and hemicellulose should be removed first. Compared to SC-DSAP, DSA-SCP involving the hemicellulose-removal-first strategy exhibited higher delignification efficiency. DSA-SCP caused lignin removal of 92.3% and the enzymatic hydrolysis was high of 97.9%. Finally, a regression model with high reliability was established to quickly evaluate pretreatment process. In summary, this study highlighted the importance of delignification for saccharification of softwood and unveiled the effect of hemicellulose on delignification.

Online determination of potassium and sodium release behaviour during single particle biomass combustion by FES and ICP-MS

This study focuses on the determination of alkali release from wood and straw pellets during combustion. The aim is to expand the knowledge on the K and Na release behaviour and to adopt chemiluminescence-based sensors for online monitoring of alkali detection which can be applied for the prevention of fouling formation in low quality biomass combustion plants. Flame emission spectrometry (FES) was used for optical detection of chemiluminescence spectra of K and Na using optical bandpass filters mounted on an ICCD (Intensified Charge Coupled Device) camera. FES data were verified by additional experiments with a single particle reactor (SPR) coupled with an inductively coupled plasma mass spectrometer (ICP-MS). Using both techniques, the release profiles of K and Na during a single pellet combustion at 1000 °C were determined and obtained K* and Na* emission intensities directly correlated with the results from the ICP-MS. It was determined that the emission intensity of alkali radicals depends on alkali concentrations in the samples and K and Na radical emission intensities increase with increasing alkali amounts in the samples. The ICP-MS data revealed that the release of K and Na mainly takes place during the stage of devolatilization. During devolatilization, almost all potassium and sodium are released from wood samples, while only 65-90% of K and 74-90% of Na are released from straw samples. Based on the results, the flame emission spectroscopy technique is capable to fully detect released alkali metals in the gas phase during combustion and proves a possibility to use flame emission sensors for monitoring the release of alkali species from biomass during combustion processes.

A novel hybrid organosolv-steam explosion pretreatment and fractionation method delivers solids with superior thermophilic digestibility to methane

Rising environmental concerns and the imminent depletion of fossil resources have sparked a strong interest towards the production of renewable energy such as biomethane. Inclusion of alternative feedstock's such as lignocellulosic biomass could further expand the production of biomethane. The present study evaluated the potential of a novel hybrid organosolv-steam explosion fractionation for delivering highly digestible pretreated solids from birch and spruce woodchips. The highest methane production yield was 176.5 mLCH₄ gVS^-1 for spruce and 327.2 mL CH₄ gVS^-1 for birch. High methane production rates of 1.0-6.3 mL min^-1 (spruce) and 6.0-35.5 mL min^-1 (birch) were obtained, leading to a rapid digestion, with 92% of total methane from spruce being generated in 80 h and 95% of that from birch in 120 h. These results demonstrate the elevated potential of the novel method to fractionate spruce and birch biomass and deliver cellulose-rich pretreated solids with superior digestibility.

Cascade processing of softwood bark with hot water extraction, pyrolysis and anaerobic digestion

A process model based on hot water extraction (HWE), slow pyrolysis and anaerobic digestion (AD) were used for pine and spruce bark utilisation. First tannins (32 mg/g and 11.8 mg/g, respectively) and polyphenols were recovered via HWE. Then, the residue was pyrolysed to produce biochar (marketable quality), gas (energy source) and liquid fractions. The liquid fraction was further separated into aqueous acidic fraction and to tar fraction. Bark, extracted bark residue and acidic liquid fraction from pyrolysis were treated in AD to produce biomethane and digestate. The methane yields from pine and spruce bark and extracted bark residue were low (from 42 to 96 mLCH4/gVSadded) and showed only small differences. In conclusion, cascade processing can improve the performance of subsequent single processes and utilise biomass sources with higher efficiency. The best processing chain may vary in different cases and the overall energy balance of processing needs further research.

Structural organization of the cell wall polymers in compression wood as revealed by FTIR microspectroscopy

Glucomannan was more strongly oriented, in line with the orientation of cellulose, than the xylan in both compression wood and normal wood of Chinese fir. Lignin in compression wood was somewhat more oriented in the direction of the cellulose microfibrils than in normal wood. The structural organization in compression wood (CW) is quite different from that in normal wood (NW). To shed more light on the structural organization of the polymers in plant cell walls, Fourier Transform Infrared (FTIR) microscopy in transmission mode has been used to compare the S₂-dominated mean orientation of wood polymers in CW with that in NW from Chinese fir (Cunninghamia lanceolata). Polarized FTIR measurements revealed that in both CW and NW samples, glucomannan and xylan showed a parallel orientation with respect to the cellulose microfibrils. In both wood samples, the glucomannan showed a much greater degree of orientation than the xylan, indicating that the glucomannan has established a stronger interaction with cellulose than xylan. For the lignin, the absorption peak also indicated an orientation along the direction of the cellulose microfibrils, but this orientation was more pronounced in CW than in NW, indicating that the lignin is affected by the orientation of the cellulose microfibrils more strongly in CW than it is in NW.

Lignin-first biomass fractionation using a hybrid organosolv - Steam explosion pretreatment technology improves the saccharification and fermentability of spruce biomass

For a transition to a sustainable society, fuels, chemicals, and materials should be produced from renewable resources. Lignocellulosic biomass constitutes an abundant and renewable feedstock; however, its successful application in a biorefinery requires efficient fractionation into its components; cellulose, hemicellulose and lignin. Here, we demonstrate that a newly established hybrid organosolv - steam explosion pretreatment can effectively fractionate spruce biomass to yield pretreated solids with high cellulose (72% w/w) and low lignin (delignification up to 79.4% w/w) content. The cellulose-rich pretreated solids present high saccharification yields (up to 61% w/w) making them ideal for subsequent bioconversion processes. Moreover, under high-gravity conditions (22% w/w) we obtained an ethanol titer of 61.7 g/L, the highest so far reported for spruce biomass. Finally, the obtained high-purity lignin is suitable for various advanced applications. In conclusion, hybrid organosolv pretreatment could offer a closed-loop biorefinery while simultaneously adding value to all biomass components.

High-efficiency second generation ethanol from the hemicellulosic fraction of softwood chips mixed with construction and demolition residues

Using lignocellulosic residues for bioethanol production could provide an alternative solution to current approaches at competitive costs once challenges related to substrate recalcitrance, process complexity and limited knowledge are overcome. Thus, the impact of different process variables on the ethanol production by Saccharomyces cerevisiae using the hemicellulosic fraction extracted through the steam-treatment of softwood chips mixed with construction and demolition residues was assessed. A statistical design of experiments approach was developed and implemented in order to identify the influencing factors (various nutrient addition sources as well as yeast inoculum growth conditions and inoculation strategies) relevant for enhancing the ethanol production potential and substrate uptake. Ethanol yields of 74.12% and monomeric sugar uptakes of 82.12 g/L were predicted and experimentally confirmed in bench and bioreactor systems. This innovative approach revealed the factors impacting the ethanol yields and carbohydrate consumption allowing powerful behavioral predictions spanning different process inputs and outputs.

Optimizing the composition of a synthetic cellulosome complex for the hydrolysis of softwood pulp: identification of the enzymatic core functions and biochemical complex characterization

BACKGROUND

The development of efficient cellulase blends is a key factor for cost-effectively valorizing biomass in a new bio-economy. Today, the enzymatic hydrolysis of plant-derived polysaccharides is mainly accomplished with fungal cellulases, whereas potentially equally effective cellulose-degrading systems from bacteria have not been developed. Particularly, a thermostable multi-enzyme cellulase complex, the cellulosome from the anaerobic cellulolytic bacterium Clostridium thermocellum is promising of being applied as cellulolytic nano-machinery for the production of fermentable sugars from cellulosic biomass.

RESULTS

In this study, 60 cellulosomal components were recombinantly produced in E. coli and systematically permuted in synthetic complexes to study the function-activity relationship of all available enzymes on Kraft pulp from pine wood as the substrate. Starting from a basic exo/endoglucanase complex, we were able to identify additional functional classes such as mannanase and xylanase for optimal activity on the substrate. Based on these results, we predicted a synthetic cellulosome complex consisting of seven single components (including the scaffoldin protein and a β-glucosidase) and characterized it biochemically. We obtained a highly thermostable complex with optimal activity around 60-65 °C and an optimal pH in agreement with the optimum of the native cellulosome (pH 5.8). Remarkably, a fully synthetic complex containing 47 single cellulosomal components showed comparable activity with a commercially available fungal enzyme cocktail on the softwood pulp substrate.

CONCLUSIONS

Our results show that synthetic bacterial multi-enzyme complexes based on the cellulosome of C. thermocellum can be applied as a versatile platform for the quick adaptation and efficient degradation of a substrate of interest.

Enabling the valorization of guaiacol-based lignin: Integrated chemical and biochemical production of cis,cis-muconic acid using metabolically engineered Amycolatopsis sp ATCC 39116

Lignin is nature's second most abundant polymer and displays a largely unexploited renewable resource for value-added bio-production. None of the lignin-based fermentation processes so far managed to use guaiacol (2-methoxy phenol), the predominant aromatic monomer in depolymerized lignin. In this work, we describe metabolic engineering of Amycolatopsis sp. ATCC 39116 to produce cis,cis-muconic acid (MA), a precursor of recognized industrial value for commercial plastics, from guaiacol. The microbe utilized a very broad spectrum of lignin-based aromatics, such as catechol, guaiacol, phenol, toluene, p-coumarate, and benzoate, tolerated them in elevated amounts and even preferred them over sugars. As a next step, we developed a novel approach for genomic engineering of this challenging, GC-rich actinomycete. The successful introduction of conjugation and blue-white screening, using β-glucuronidase, enabled tailored genomic modifications within ten days. Successive deletion of two putative muconate cycloisomerases from the genome provided the mutant Amycolatopsis sp. ATCC 39116 MA-2, which accumulated 3.1gL^-1 MA from guaiacol within 24h, achieving a yield of 96%. The mutant was found also capable to produce MA from a guaiacol-rich true lignin hydrolysate, obtained from pine through hydrothermal conversion. This provides an important proof-of-concept to successfully coupling chemical and biochemical process steps into a value chain from the lignin polymer to an industrial chemical. In addition, Amycolatopsis sp. ATCC 39116 MA-2 was able to produce 2-methyl MA from o-cresol (2-methyl phenol), which opens possibilities towards polymers with novel architecture and properties.

Comparison of [HSO4]-, [Cl]- and [MeCO2]- as anions in pretreatment of aspen and spruce with imidazolium-based ionic liquids

Background

Ionic liquids (ILs) draw attention as green solvents for pretreatment of lignocellulose before enzymatic saccharification. Imidazolium-based ILs with different anionic constituents ([HSO₄]⁻, [Cl]⁻, [MeCO₂]⁻) were compared with regard to pretreatment of wood from aspen and spruce. The objective was to elucidate how the choice of anionic constituent affected the suitability of using the IL for pretreatment of hardwood, such as aspen, and softwood, such as spruce. The investigation covered a thorough analysis of the mass balance of the IL pretreatments, the effects of pretreatment on the cell wall structure as assessed by fluorescence microscopy, and the effects of pretreatment on the susceptibility to enzymatic saccharification. Torrefied aspen and spruce were included in the comparison for assessing how shifting contents of hemicelluloses and Klason lignin affected the susceptibility of the wood to IL pretreatment and enzymatic saccharification.

Results

The glucose yield after IL pretreatment increased in the order [Cl]⁻ < [HSO₄]⁻ < [MeCO₂]⁻ for aspen, but in the order [HSO₄]⁻ < [Cl]⁻ < [MeCO₂]⁻ for spruce. For both aspen and spruce, removal of hemicelluloses and lignin increased in the order [Cl]⁻ < [MeCO₂]⁻ < [HSO₄]⁻. Fluorescence microscopy indicated increasingly disordered cell wall structure following the order [HSO₄]⁻ < [Cl]⁻ < [MeCO₂]⁻. Torrefaction of aspen converted xylan to pseudo-lignin and changed the glucose yield order to [HSO₄]⁻ < [Cl]⁻ < [MeCO₂]⁻.

Conclusions

The acidity of [HSO₄]⁻ caused extensive hydrolysis of xylan, which facilitated pretreatment of xylan-rich hardwood. Apart from that, the degree of removal of hemicelluloses and lignin did not correspond well with the improvement of the enzymatic saccharification. Taken together, the saccharification results were found to mainly reflect (i) the different capacities of the ILs to disorder the cell wall structure, (ii) the recalcitrance caused by high xylan content, and (iii) the capacity of the [HSO₄]⁻-based IL to hydrolyze xylan.

Electronic supplementary material

The online version of this article (10.1186/s12896-017-0403-0) contains supplementary material, which is available to authorized users.

Removal of Water-Soluble Extractives Improves the Enzymatic Digestibility of Steam-Pretreated Softwood Barks

Softwood bark contains a large amounts of extractives—i.e., soluble lipophilic (such as resin acids) and hydrophilic components (phenolic compounds, stilbenes). The effects of the partial removal of water-soluble extractives before acid-catalyzed steam pretreatment on enzymatic digestibility were assessed for two softwood barks—Norway spruce and Scots pine. A simple hot water extraction step removed more than half of the water-soluble extractives from the barks, which improved the enzymatic digestibility of both steam-pretreated materials. This effect was more pronounced for the spruce than the pine bark, as evidenced by the 30 and 11% glucose yield improvement, respectively, in the enzymatic digestibility. Furthermore, analysis of the chemical composition showed that the acid-insoluble lignin content of the pretreated materials decreased when water-soluble extractives were removed prior to steam pretreatment. This can be explained by a decreased formation of water-insoluble “pseudo-lignin” from water-soluble bark phenolics during the acid-catalyzed pretreatment, which otherwise results in distorted lignin analysis and may also contribute to the impaired enzymatic digestibility of the barks. Thus, this study advocates the removal of extractives as the first step in the processing of bark or bark-rich materials in a sugar platform biorefinery.

Pilot-scale steam explosion pretreatment with 2-naphthol to overcome high softwood recalcitrance

BACKGROUND

Steam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries. It is however not effective for overcoming the extremely high recalcitrance of softwood to biochemical conversion. Recent fundamental research in small-scale liquid hot water pretreatment has shown, though, that the addition of a carbocation scavenger like 2-naphthol can prevent lignin repolymerization and thus enhance the enzymatic digestibility of softwood cellulose. This work studies the technical application potential of this approach in a larger steam explosion pilot plant for surmounting softwood recalcitrance.

RESULTS

The addition of 35.36 g 2-naphthol to the steam explosion pretreatment of 1.5 kg spruce wood chips allowed to considerably enhance the enzymatic cellulose digestibility. Different ways of adding the solid 2-naphthol to steam pretreatment were tested. Mixing with the biomass before pretreatment could enhance digestibility by up to 55% compared to control experiments. Impregnation of the biomass with 2-naphthol was yet more effective. Acetone and ethanol were tested to dissolve 2-naphthol and impregnate the biomass. The solvents were then removed again by evaporation before the pretreatment. The impregnation allowed to enhance digestibility by up to 179 and 192%, respectively. A comparison to prevalent acid-catalyzed steam explosion pretreatments for softwood revealed that the scavenger approach allows for obtaining exceptionally high yields in enzymatic hydrolysis. The biomass impregnation with 2-naphthol even renders a complete enzymatic cellulose conversion possible, which is remarkable for a softwood pretreatment not removing lignin. Steam pretreatment experiments without explosive decompression revealed that the enhancing effects of the explosion and the scavenger complement each other well. The explosion enhances the accessibility of the cellulose while the use of the scavenger reduces particularly the deactivation of enzymes.

CONCLUSIONS

This is the first study to show that a carbocation scavenger in steam pretreatment can enhance the enzymatic digestibility of lignocellulosic biomass. The approach opens up a novel possibility for overcoming the high softwood recalcitrance in a process that does not require an acid catalyst or the removal of lignin from the biomass.

A mild thermomechanical process for the enzymatic conversion of radiata pine into fermentable sugars and lignin

BACKGROUND

Conversion of softwoods into sustainable fuels and chemicals is important for parts of the world where softwoods are the dominant forest species. While they have high theoretical sugar yields, softwoods are amongst the most recalcitrant feedstocks for enzymatic processes, typically requiring both more severe pretreatment conditions and higher enzyme doses than needed for other lignocellulosic feedstocks. Although a number of processes have been proposed for converting softwoods into sugars suitable for fuel and chemical production, there is still a need for a high-yielding, industrially scalable and cost-effective conversion route.

RESULTS

We summarise work leading to the development of an efficient process for the enzymatic conversion of radiata pine (Pinus radiata) into wood sugars. The process involves initial pressurised steaming of wood chips under relatively mild conditions (173 °C for 3-72 min) without added acid catalyst. The steamed chips then pass through a compression screw to squeeze out a pressate rich in solubilised hemicelluloses. The pressed chips are disc-refined and wet ball-milled to produce a substrate which is rapidly saccharified using commercially available enzyme cocktails. Adding 0.1% polyethylene glycol during saccharification was found to be particularly effective with these substrates, reducing enzyme usage to acceptable levels, e.g. 5 FPU/g OD substrate. The pressate is separately hydrolysed using acid, providing additional hemicellulose-derived sugars, for an overall sugar yield of 535 kg/ODT chips (76% of theoretical). The total pretreatment energy input is comparable to other processes, with the additional energy for attrition being balanced by a lower thermal energy requirement. This pretreatment strategy produces substrates with low levels of fermentation inhibitors, so the glucose-rich mainline and pressate syrups can be fermented to ethanol without detoxification. The lignin from the process remains comparatively unmodified, as evident from the level of retained β-ether interunit linkages, providing an opportunity for conversion into saleable co-products.

CONCLUSIONS

This process is an efficient route for the enzymatic conversion of radiata pine, and potentially other softwoods, into a sugar syrup suitable for conversion into fuels and chemicals. Furthermore, the process uses standard equipment that is largely proven at commercial scale, de-risking process scale-up.

Removal of glucuronic acid from xylan is a strategy to improve the conversion of plant biomass to sugars for bioenergy

BACKGROUND

Plant lignocellulosic biomass can be a source of fermentable sugars for the production of second generation biofuels and biochemicals. The recalcitrance of this plant material is one of the major obstacles in its conversion into sugars. Biomass is primarily composed of secondary cell walls, which is made of cellulose, hemicelluloses and lignin. Xylan, a hemicellulose, binds to the cellulose microfibril and is hypothesised to form an interface between lignin and cellulose. Both softwood and hardwood xylan carry glucuronic acid side branches. As xylan branching may be important for biomass recalcitrance and softwood is an abundant, non-food competing, source of biomass it is important to investigate how conifer xylan is synthesised.

RESULTS

Here, we show using Arabidopsis gux mutant biomass that removal of glucuronosyl substitutions of xylan can allow 30% more glucose and over 700% more xylose to be released during saccharification. Ethanol yields obtained through enzymatic saccharification and fermentation of gux biomass were double those obtained for non-mutant material. Our analysis of additional xylan branching mutants demonstrates that absence of GlcA is unique in conferring the reduced recalcitrance phenotype. As in hardwoods, conifer xylan is branched with GlcA. We use transcriptomic analysis to identify conifer enzymes that might be responsible for addition of GlcA branches onto xylan in industrially important softwood. Using a combination of in vitro and in vivo activity assays, we demonstrate that a white spruce (Picea glauca) gene, PgGUX, encodes an active glucuronosyl transferase. Glucuronic acid introduced by PgGUX reduces the sugar release of Arabidopsis gux mutant biomass to wild-type levels indicating that it can fulfil the same biological function as native glucuronosylation.

CONCLUSION

Removal of glucuronic acid from xylan results in the largest increase in release of fermentable sugars from Arabidopsis plants that grow to the wild-type size. Additionally, plant material used in this work did not undergo any chemical pretreatment, and thus increased monosaccharide release from gux biomass can be achieved without the use of environmentally hazardous chemical pretreatment procedures. Therefore, the identification of a gymnosperm enzyme, likely to be responsible for softwood xylan glucuronosylation, provides a mutagenesis target for genetically improved forestry trees.

Characterization and Comparison of Fast Pyrolysis Bio-oils from Pinewood, Rapeseed Cake, and Wheat Straw Using 13C NMR and Comprehensive GC × GC

Fast pyrolysis bio-oils are feasible energy carriers and a potential source of chemicals. Detailed characterization of bio-oils is essential to further develop its potential use. In this study, quantitative ¹³C nuclear magnetic resonance (¹³C NMR) combined with comprehensive two-dimensional gas chromatography (GC × GC) was used to characterize fast pyrolysis bio-oils originated from pinewood, wheat straw, and rapeseed cake. The combination of both techniques provided new information on the chemical composition of bio-oils for further upgrading. ¹³C NMR analysis indicated that pinewood-based bio-oil contained mostly methoxy/hydroxyl (≈30%) and carbohydrate (≈27%) carbons; wheat straw bio-oil showed to have high amount of alkyl (≈35%) and aromatic (≈30%) carbons, while rapeseed cake-based bio-oil had great portions of alkyl carbons (≈82%). More than 200 compounds were identified and quantified using GC × GC coupled to a flame ionization detector (FID) and a time of flight mass spectrometer (TOF-MS). Nonaromatics were the most abundant and comprised about 50% of the total mass of compounds identified and quantified via GC × GC. In addition, this analytical approach allowed the quantification of high value-added phenolic compounds, as well as of low molecular weight carboxylic acids and aldehydes, which exacerbate the unstable and corrosive character of the bio-oil.

Micromorphological changes and mechanism associated with wet ball milling of Pinus radiata substrate and consequences for saccharification at low enzyme loading

In this work, substrates prepared from thermo-mechanical treatment of Pinus radiata chips were vibratory ball milled for different times. In subsequent enzymatic hydrolysis, percent glucan conversion passed through a maximum value at a milling time of around 120min and then declined. Scanning electron microscopy revealed breakage of fibers to porous fragments in which lamellae and fibrils were exposed during ball milling. Over-milling caused compression of the porous fragments to compact globular particles with a granular texture, decreasing accessibility to enzymes. Carbon-13 NMR spectroscopy showed partial loss of interior cellulose in crystallites, leveling off once fiber breakage was complete. A mathematical model based on observed micromorphological changes supports ball milling mechanism. At a low enzyme loading of 2FPU/g of substrate and milling time of 120min gave a total monomeric sugar yield of 306g/kg of pulp which is higher than conventional pretreatment method such as steam exploded wood.

Steam explosion pretreatment of softwood: the effect of the explosive decompression on enzymatic digestibility

BACKGROUND

Steam explosion pretreatment has been examined in many studies for enhancing the enzymatic digestibility of lignocellulosic biomass and is currently the most common pretreatment method in commercial biorefineries. The information available about the effect of the explosive decompression on the biochemical conversion is, however, very limited, and no studies prove that the latter is actually enhanced by the explosion. Hence, it is of great value to discern between the effect of the explosion on the one hand and the steaming on the other hand, to identify their particular influences on enzymatic digestibility.

RESULTS

The effect of the explosive decompression in the steam explosion pretreatment of spruce wood chips on their enzymatic cellulose digestibility was studied systematically. The explosion had a high influence on digestibility, improving it by up to 90 % compared to a steam pretreatment without explosion. Two factors were identified to be essentially responsible for the effect of the explosion on enzymatic digestibility: pretreatment severity and pressure difference of the explosion. A higher pretreatment severity can soften up and weaken the lignocellulose structure more, so that the explosion can better break up the biomass and decrease its particle size, which enhances its digestibility. In particular, increasing the pressure difference of the explosion leads to more defibration, a smaller particle size and a better digestibility. Though differences were found in the micro- and nanostructure of exploded and non-exploded biomass, the only influence of the explosion on digestibility was found to be the macroscopic particle size reduction. Steam explosion treatments with a high severity and a high pressure difference of the explosion lead to a comparatively high cellulose digestibility of the-typically very recalcitrant-softwood biomass.

CONCLUSIONS

This is the first study to show that explosion can enhance the enzymatic digestibility of lignocellulosic biomass. If the enhancing effect of the explosion is thoroughly exploited, even very recalcitrant biomass like softwood can be made enzymatically digestible.

Woodworkers and the inflammatory effects of softwood/hardwood dust: evidence from nasal cytology

Our primary aim was to use nasal cytology to compare a group of woodworkers with a group of unexposed subjects to see whether wood dust exposure correlates with specific patterns of inflammatory or infectious rhinitis. A secondary aim was to seek any differences in nasal symptoms or nasal cytology between workers exposed to softwood vs hardwood dust, thereby comparing the inflammatory harmful potential of the two woods. Among 117 woodworkers at factories in the Veneto region (Italy), 40 exposed to either softwood or hardwood dust were assessed by means of a questionnaire, nasal cytology, and personal wood dust sampling, and compared with 40 unexposed controls. Woodworkers reported significantly more nasal symptoms than controls (p = 0.0007). The woodworker group's nasal smears contained significantly more neutrophils (p < 0.00001) and lymphocytes (p = 0.02) than the control group's. The softwood workers had significantly lower levels of personal exposure to wood dust than the hardwood workers (p = 0.04); there were no significant differences in age, history of cigarette smoking, or period of exposure between these two sub-cohorts of woodworkers. A statistical trend indicated that softwood workers had more eosinophils (p = 0.05) and lymphocytes (p = 0.05) in their rhinocytograms. Nasal cytology revealed chronic inflammatory rhinitis in a significant proportion of woodworkers' enroled in this study. It also suggested a different harmful potential for softwood and hardwood dust. Nasal cytology could prove useful in screening woodworkers for chronic inflammatory rhinitis. Further investigations are needed to examine the role of different types of wood dust in nasal inflammation.

High-alkali low-temperature polysulfide pulping (HALT) of Scots pine

High-alkali low-temperature polysulfide pulping (HALT) was effectively utilised to prevent major polysaccharide losses while maintaining the delignification rate. A yield increase of 6.7 wt% on wood was observed for a HALT pulp compared to a conventionally produced kappa number 60 pulp with comparable viscosity. Approximately 70% of the yield increase was attributed to improved galactoglucomannan preservation and 30% to cellulose. A two-stage oxygen delignification sequence with inter-stage peroxymonosulphuric acid treatment was used to ensure delignification to a bleachable grade. In a comparison to conventional pulp, HALT pulp effectively maintained its yield advantage. Diafiltration trials indicate that purified black liquor can be directly recycled, as large lignin fractions and basically all dissolved polysaccharides were separated from the alkali-rich BL.

Chemical characteristics and enzymatic saccharification of lignocellulosic biomass treated using high-temperature saturated steam: comparison of softwood and hardwood

This study investigated the effect of high-temperature saturated steam treatments on the chemical characteristics and enzymatic saccharification of softwood and hardwood. The weight loss and chemical modification of cedar and beech wood pieces treated at 25, 35, and 45 atm for 5 min were determined. Fourier transform infrared and X-ray diffraction analyses indicated that solubilization and removal of hemicellulose and lignin occurred by the steam treatment. The milling treatment of steam-treated wood enhanced its enzymatic saccharification. Maximum enzymatic saccharification (i.e., 94% saccharification rate of cellulose) was obtained using steam-treated beech at 35 atm for 5 min followed by milling treatment for 1 min. However, the necessity of the milling treatment for efficient enzymatic saccharification is dependent on the wood species.

Improved saccharification of steam-exploded Pinus radiata on supplementing crude extract of Penicillium sp

Commercially available enzymes do not contain all the necessary softwood-specific accessory enzymes to obtain high saccharification efficiency. In this work, six saprophytic fungi obtained from Pinus radiata plantation site were screened for the putative softwood-specific accessory enzyme, β-mannanase. A Penicillium sp. was found to produce β-mannanase in both solid (31.6 units/g of dry biomass) and liquid (117 units/g of dry biomass) cultures using locust bean gum as an inducer after 2 weeks of incubation. The saccharification of steam-exploded Pinus radiata was 7.8 % w/w improved when the crude extract of Penicillium sp. was added to a mixture of commercial enzymes.

Optimization of chip size and moisture content to obtain high, combined sugar recovery after sulfur dioxide-catalyzed steam pretreatment of softwood and enzymatic hydrolysis of the cellulosic component

The influence of chip size and moisture content on the combined sugar recovery after steam pretreatment of lodgepole pine and subsequent enzymatic hydrolysis of the cellulosic component were investigated using response surface methodology. Chip size had little influence on sugar recovery after both steam pretreatment and enzymatic hydrolysis. In contrast, the moisture of the chips greatly influenced the relative severity of steam pretreatment and, as a result, the combined sugar recovery from the hemicellulosic and cellulosic fractions. Irrespective of chip size and the pretreatment temperature, time, and SO2 loading that were used, the relative severity of pretreatment was highest at a moisture of 30-40w/w%. However, the predictive model indicated that an elevated moisture content of roughly 50w/w% (about the moisture content of a standard softwood mill chip) would result in the highest, combined sugar recovery (80%) over the widest range of steam pretreatment conditions.

Influence of bark on fuel ethanol production from steam-pretreated spruce

BACKGROUND

Bark and bark-containing forest residues have the potential for utilization as raw material for lignocellulosic ethanol production due to their abundance and low cost. However, the different physical properties and chemical composition of bark compared to the conventionally used wood chips may influence the spruce-to-ethanol bioconversion process. This study assesses the impact of bark on the overall bioconversion in two process configurations, separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF), utilizing steam-pretreated spruce bark and wood mixtures.

RESULTS

Mixtures of different proportions of spruce bark and wood chips were subjected to SO2-catalyzed steam pretreatment at 210°C for five minutes, which has been shown to be effective for the pretreatment of spruce wood chips. The final ethanol concentration was the highest without bark and decreased significantly with increasing proportions of bark in both process configurations. However, this decrease cannot be attributed solely to the lower availability of the carbohydrates in mixtures containing bark, as the ethanol yield also decreased, from 85 to 59% in SSF and from 84 to 51% in SHF, as the mass fraction of bark was increased from 0 to 100%.

CONCLUSIONS

The results show that it was significantly more difficult to hydrolyse spruce bark to monomeric sugars than wood chips. Bark had an adverse effect on the whole bioconversion process due to its lower enzymatic hydrolyzability. On the other hand, bark inclusion had no detrimental effect on the fermentability of steam-pretreated spruce wood and bark mixtures. It was also observed that lower amounts of inhibitory degradation products were formed during the steam pretreatment of spruce bark than during the steam pretreatment of wood chips.

Organosolv pretreatment of Sitka spruce wood: conversion of hemicelluloses to ethyl glycosides

A range of Organosolv pretreatments, using ethanol:water mixtures with dilute sulphuric acid, were applied to Sitka spruce sawdust with the aim of generating useful co-products as well as improving saccharification yield. The most efficient of the pretreatment conditions, resulting in subsequent saccharification yields of up to 86%, converted a large part of the hemicellulose sugars to their ethyl glycosides as identified by GC/MS. These conditions also reduced conversion of pentoses to furfural, the ethyl glycosides being more stable to dehydration than the parent pentoses. Through comparison with the behaviour of model compounds under the same reaction conditions it was shown that the anomeric composition of the products was consistent with a predominant transglycosylation reaction mechanism, rather than hydrolysis followed by glycosylation. The ethyl glycosides have potential as intermediates in the sustainable production of high-value chemicals.

Alkaline hydrogen peroxide pretreatment of softwood: hemicellulose degradation pathways

This study investigated softwood hemicelluloses degradation pathways during alkaline hydrogen peroxide (AHP) pretreatment of Douglas fir. It was found that glucomannan is much more susceptible to alkaline pretreatment than xylan. Organic acids, including lactic, succinic, glycolic and formic acid are the predominant products from glucomannan degradation. At low treatment temperature (90°C), a small amount of formic acid is produced from glucomannan, whereas glucomannan degradation to lactic acid and succinic acid becomes the main reactions at 140°C and 180°C. The addition of H2O2 during alkaline pretreatment of D. fir led to a significant removal of lignin, which subsequently facilitated glucomannan solubilization. However, H2O2 has little direct effect on the glucomannan degradation reaction. The main degradation pathways involved in glucomannan conversion to organics acids are elucidated. The results from this study demonstrate the potential to optimize pretreatment conditions to maximize the value of biomass hemicellulose.

Effect of high dry solids loading on enzymatic hydrolysis of acid bisulfite pretreated Eastern redcedar

This study investigates hydrolysis of cellulose from Eastern redcedar to glucose at high solids loading. Enzymatic hydrolysis of pretreated redcedar was performed with 0.5 ml Accelerase® 1500/g glucan (46 FPU/g glucan) using dry solids loading from 2% to 20% (w/w). Rheological challenges observed at high solids loading were overcome by adding stainless steel balls to shake flask reactors. The highest glucose concentration, 126 g/L (84% glucan-to-glucose yield), was obtained using 20% solids loading with stainless steel balls as a mixing aid. This enzymatic hydrolyzate was fermented into ethanol using Saccharomyces cerevisiae D5A to produce 52 g/L of ethanol (corresponding to 166 L/dry Mg of redcedar). Reducing enzyme dosage at 16% solids loading from 46 to 11.5 FPU/g glucan reduced glucan-to-glucose yields. This study has demonstrated the possibility of extracting sugars from the invasive species of Eastern redcedar with high solid loadings and their conversion into ethanol.