Rodger P. Beatson

The effect of fiber characteristics on hydrolysis and cellulase accessibility to softwood substrates

The effect of gross fiber characteristics on enzyme accessibility and hydrolysis of Douglas fir kraft pulp substrates was investigated. The average fiber size and coarseness of the substrate had a significant effect on the enzyme adsorption capacity. This was primarily due to the increased specific surface area of small fibers and fines. The observed adsorption capacities were in agreement with the hydrolysis rates and yields because the substrates with the lower average fiber size were hydrolyzed both at a faster rate and more completely. The observed changes in fiber-length distribution and fiber coarseness suggested that the effect of fiber size was most influential during the initial stages of hydrolysis. The small fibers and fines present in heterogeneous, lignocellulosic substrates were hydrolyzed rapidly, yielding a high initial rate of hydrolysis.

Optimization of Steam Explosion to Enhance Hemicellulose Recovery and Enzymatic Hydrolysis of Cellulose in Softwoods

A combination of Douglas fir heartwood and sapwood chips were steam pretreated under three conditions as measured by the Severity Factor (log Ro), which incorporated the time, temperature/pressure of pretreatment. By adjusting the steam pretreatment conditions, it was hoped to recover the majority of the hemicellulose component as monomers in the water-soluble stream, while providing a cellulosic-rich, water-insoluble fraction that could be readily hydrolyzed by cellulases. These three conditions were chosen to represent either high hemicellulose sugar recovery (low severity [L], log Ro=3.08), high-enzyme hydrolyzability of the cellulosic component (high severity [H], log Ro=4.21), and a compromise between the two conditions (medium severity [M], log Ro=3.45). The medium-severity pretreatment conditions (195°C, 4.5 min, 4.5% SO2 logRo=3.45) gave the best compromise in terms of relatively high hemicellulose recovery after stream pretreatment and the subsequent efficiency of enzymatic hydrolysis of the water-insoluble cellulosic fraction. The percent recovery of the original hemicellulose in the water-soluble fraction dropped significantly when the severity was increased (L-76.8%, M-64.7%, and H-37.5%). However, the ease of enzymatic hydrolysis of the cellulose-rich, water-insoluble fraction increased with increasing severity (L-24%, M-86.6%, and H-97.9%). Although more severe pretreatment conditions provided optimum hydrolysis of the cellulosic component, less severe conditions resulted in better recovery of the combined hemicellulose and cellulosic components.

The Nature of Lignin from Steam Explosion/Enzymatic Hydrolysis of Softwood

Effective utilization of the lignin by-product is a prerequisite to the commercial viability of ethanol production from softwood wastes using a steam explosion (SE)/enzymatic hydrolysis (EH)/fermentation process. Changes in the chemical composition of Douglas fir wood on SO2-catalyzed SE followed by EH were assessed using conventional analytical methods and new halogen-probetechniques. A significant solubilization of hemicelluloses was observed in the SE stage, the severity of which affected subsequent fermentation of cellulose and sorption of enzymes. SE of softwood resulted in dramatic changes in the chemical structure of lignin in the residual material involving chemical reactions via the benzyl cation. This leads to a more condensed lignin with partly blocked α-reaction centres. Possible uses for this lignin are discussed.

Rapid, microscale, acetyl bromide-based method for high-throughput determination of lignin content in Arabidopsis thaliana.

The acetyl bromide method has been modified to enable the rapid microscale determination of lignin content in Arabidopsis with the goal of determining the genes that control lignin in plants. Modifications include reduction in sample size, use of a microball mill, adoption of a modified rapid method of extraction, use of an ice-bath to stabilize solutions and reduction in the volume of solutions. The microscale method was shown to be rapid, accurate and precise with values in agreement with those determined by the full-scale acetyl bromide method. The extinction coefficient for Arabidopsis lignin, dissolved using acetyl bromide, was determined to be 23.35 g(-1) L cm(-1) at 280 nm. This value is independent of the Arabidopsis accession, environmental growth conditions and is insensitive to lignin structure. The newly developed method can be used to determine lignin content in the inflorescence stems of Arabidopsis for mapping of lignin-related genes.

The nature of lignin from steam explosion/ enzymatic hydrolysis of softwood: structural features and possible uses: scientific note.

Effective utilization of the lignin by-product is a prerequisite to the commercial viability of ethanol production from softwood wastes using a steam explosion (SE)/enzymatic hydrolysis (EH)/fermentation process. Changes in the chemical composition of Douglas fir wood on SO2-catalyzed SE followed by EH were assessed using conventional analytical methods and new halogen-probetechniques. A significant solubilization of hemicelluloses was observed in the SE stage, the severity of which affected subsequent fermentation of cellulose and sorption of enzymes. SE of softwood resulted in dramatic changes in the chemical structure of lignin in the residual material involving chemical reactions via the benzyl cation. This leads to a more condensed lignin with partly blocked α-reaction centres. Possible uses for this lignin are discussed.

Characterization of the polyphenolics related to the colour of western red cedar (Thuja plicata Donn) heartwood.

Summary Three quarters of the western red cedars heartwood colour is due to a polymeric material easily isolated by methanol extraction. The nature of this polymer has not been fully investigated and published information is contradictory. Our initial examination of the coloured polymer by pyrolysis-gas chromatography, combined with mass spectrometry, indicated that the polymer was guaiacyl in nature and thus similar to softwood lignin. However, analysis by infrared spectroscopy indicated the presence of both lignin and lignan like moieties. To clarify this issue a more detailed analysis was conducted using nuclear magnetic resonance spectroscopy (1H NMR, 31P NMR, 13C NMR). Analysis of the spectra and comparison with the spectra of plicatic acid and a product from mild acid treatment of plicatic acid, indicated that the polymeric fraction was derived almost entirely from lignans. During polymer formation, the highly reactive pyrocatechol moiety in the plicatic acid is destroyed, leaving a guaiacyl-like polymer. The reaction mechanism appears to proceed via an ortho-quinone intermediate followed by polymerization.

Enzyme treatments of the dissolved and colloidal substances present in mill white water and the effects on the resulting paper properties

Abstract The composition of the dissolved and colloidal fractions of a “model” white water prepared from a spruce-pine-fir/hemlock thermomechanical pulp was determined. The impact of these fractions on paper properties was assessed and the ability of enzymes to degrade the different components was investigated. The colloidal particles in the white water had an average size of 0.5 μm and a size range from 0.1 μm to 2 μm. Lignins, resin and fatty acids, and esterified extractives, such as sterol esters and triglycerides, were the main constituents of the colloidal particles, while the lignans and neutral polysaccharides were predominantly dissolved in the white water. Reductions in paper strength were mainly caused by the dissolved substances, whereas the colloidal substances were primarily responsible for the reduction in paper porosity and optical properties. Added laccases were able to degrade most of the extractives while lipases specifically hydrolyzed esterified extractives present in the colloidal fraction.

Identification of quantitative trait loci controlling fibre length and lignin content in Arabidopsis thaliana stems

Fibre properties and the biochemical composition of cell walls are important traits in many applications. For example, the lengths of fibres define the strength and quality of paper, and lignin content is a critical parameter for the use of biomass in biofuel production. Identifying genes controlling these traits is comparatively difficult in woody species, because of long generation times and limited amenability to high-resolution genetic mapping. To address this problem, this study mapped quantitative trait loci (QTLs) defining fibre length and lignin content in the Arabidopsis recombinant inbred line population Col-4×Ler-0. Adapting high-throughput phenotyping techniques for both traits for measurements in Arabidopsis inflorescence stems identified significant QTLs for fibre length on chromosomes 2 and 5, as well as one significant QTL affecting lignin content on chromosome 2. For fibre length, total variation within the population was 208% higher than between parental lines and the identified QTLs explained 50.58% of the observed variation. For lignin content, the values were 261 and 26.51%, respectively. Bioinformatics analysis of the associated intervals identified a number of candidate genes for fibre length and lignin content. This study demonstrates that molecular mapping of QTLs pertaining to wood and fibre properties is possible in Arabidopsis, which substantially broadens the use of Arabidopsis as a model species for the functional characterization of plant genes.

The nature of chromophores in high-extractives mechanical pulps: Western red cedar (Thuja plicata Donn) chemithermomechanical pulp (CTMP)

Abstract The utilization of western red cedar mechanical pulp is limited by low brightness caused by a high chromophore content. In this paper we identify these chromophores and provide a possible mechanism for their formation during the mechanical pulping process. Diffuse reflectance ultraviolet (DRUV) and Fourier-transform infrared (DRIFT) spectra were recorded for western red cedar chemimechanical pulp treated with hydrogen peroxide, sodium borohydride and acetic anhydride. Treatment with hydrogen peroxide was conducted over different time periods. The spectra indicate that three carbonyl-containing chromophores contribute to light absorption in the visible region. Two conjugated ortho-quinones contributed most of the color. These quinones were formed by oxidation and polymerization of lignans during the refining process. The third chromophore was coniferaldehyde. There was a large initial time lag for the reaction of peroxide with coniferaldehyde relative to reaction time with the quinones. We ascribe this to differences in topochemistry. It was deduced that coniferaldehyde was mainly associated with lignin in the interior of the fiber wall, whereas the quinones were derived from lignans that had been deposited on the fiber surface. Identification of the three chromophores provides a basis for studies of the kinetics of brightening of western red cedar mechanical pulps.

Increasing efficiency of enzymatic hemicellulose removal from bamboo for production of high-grade dissolving pulp

To improve the efficiency of enzymatic hemicellulose removal from bamboo pre-hydrolysis kraft pulp, mechanical refining was conducted prior to enzyme treatment. Refining significantly improved the subsequent hemicellulose removal efficiency by xylanase treatment. Results showed that when PFI refining was followed by 3h xylanase treatment, the xylan content of the bamboo pre-hydrolysis kraft pulp (after first stage oxygen delignification) could be decreased to 2.72% (w/w). After bleaching of enzyme treated pulp, the alpha-cellulose content was 93.4% (w/w) while the xylan content was only 2.38%. The effect of refining on fibre properties was investigated in terms of freeness, water retention value, fibre length and fibrillation characteristics. The brightness, reactivity and viscosity were also determined to characterize the quality of final pulp. Results demonstrated the feasibility of combining refining and xylanase treatment to produce high quality bamboo dissolving pulp.