No abstract

No abstract

Twenty-one organosolv ethanol lignin samples were prepared from hybrid poplar (Populus nigra xP. maximowiczii) under varied conditions with an experimental matrix designed using response surface methodology (RSM). The lignin preparations were evaluated as potential antioxidants. Results indicated that the lignins with more phenolic hydroxyl groups, less aliphatic hydroxyl groups, low molecular weight, and narrow polydispersity showed high antioxidant activity. Processing conditions affected the functional groups and molecular weight of the extracted organosolv ethanol lignins, and consequently influenced the antioxidant activity of the lignins. In general, the lignins prepared at elevated temperature, longer reaction time, increased catalyst, and diluted ethanol showed high antioxidant activity. Regression models were developed to enable the quantitative prediction of lignin characteristics and antioxidant activity based on the processing conditions.

No abstract

Pulps with residual lignin ranging from 6.4-27.4% (w/w) were prepared from mixed softwoods using a proprietary biorefining technology (the Lignol process) based on aqueous ethanol organosolv extraction. The pulps were evaluated for bioconversion using enzymatic hydrolysis of the cellulose fraction to glucose and subsequent fermentation to ethanol. All pulps were readily hydrolyzed without further delignification. More than 90% of the cellulose in low lignin pulps (< or =18.4% residual lignin) was hydrolyzed to glucose in 48 h using an enzyme loading of 20 filter paper units/g cellulose. Cellulose in a high lignin pulp (27.4% residual lignin) was hydrolyzed to >90% conversion within 48 h using 40 filter paper units/g. The pulps performed well in both sequential and simultaneous saccharification and fermentation trials indicating an absence of metabolic inhibitors. Chemical and physical analyses showed that lignin extracted during organosolv pulping of softwood is a suitable feedstock for production of lignin-based adhesives and other products due to its high purity, low molecular weight, and abundance of reactive groups. Additional co-products may be derived from the hemicellulose sugars and furfural recovered from the water-soluble stream.

An organosolv process involving extraction with hot aqueous ethanol has been evaluated for bioconversion of hybrid poplar to ethanol. The process resulted in fractionation of poplar chips into a cellulose-rich solids fraction, an ethanol organosolv lignin (EOL) fraction, and a water-soluble fraction containing hemicellulosic sugars, sugar breakdown products, degraded lignin, and other components. The influence of four independent process variables (temperature, time, catalyst dose, and ethanol concentration) on product yields was analyzed over a broad range using a small composite design and response surface methodology. Center point conditions for the composite design (180 degrees C, 60 min, 1.25% H(2)SO(4), and 60% ethanol), yielded a solids fraction containing approximately 88% of the cellulose present in the untreated poplar. Approximately 82% of the total cellulose in the untreated poplar was recovered as monomeric glucose after hydrolysis of the solids fraction for 24 h using a low enzyme loading (20 filter paper units of cellulase/g cellulose); approximately 85% was recovered after 48 h hydrolysis. Total recovery of xylose (soluble and insoluble) was equivalent to approximately 72% of the xylose present in untreated wood. Approximately 74% of the lignin in untreated wood was recovered as EOL. Other cooking conditions resulted in either similar or inferior product yields although the distribution of components between the various fractions differed markedly. Data analysis generated regression models that describe process responses for any combination of the four variables.

Multidimensional, multinuclear nuclear magnetic resonance spectroscopy combined with dynamical simulated annealing has been used to determine the structure of a 110 amino acid cellulose-binding domain (CBD) from Cex, a beta-1,4-glycanase from the bacterium Cellulomonas fimi (CBDcex). An experimental data set comprising 1795 interproton NOE-derived restraints, 50 phi, 34 chi 1, and 106 hydrogen bond restraints was used to calculate 20 final structures. The calculated structures have an average root-mean-square (rms) deviation about the mean structure of 0.41 A for backbone atoms and 0.67 A for all heavy atoms when fitted over the secondary structural elements. Chromatography, ultracentrifugation, and 15N NMR relaxation experiments demonstrate that CBDcex is a dimer in solution. While attempts to measure NOEs across the dimer interface were unsuccessful, a computational strategy was employed to generate dimer structures consistent with the derived data set. The results from the dimer calculations indicate that, while the monomer topologies produced in the context of the dimer can be variable, the relative positioning of secondary structural elements and side chains present in the monomer are restored upon dimer formation. CBDcex forms an extensive beta-sheet structure with a beta-barrel fold. Titration with cellohexaose, [beta-D-glucopyranosyl-(1,4)]5-D-glucose, establishes that Trp 54 and 72 participate in cellulose binding. Analysis of the structure shows that these residues are adjacent in space and exposed to solvent. Together with other proximate hydrophilic residues, these residues form a carbohydrate-binding cleft, which appears to be a feature common to all CBDs of the same family.

The ability of a commercial Trichoderma reesei cellulase preparation (Celluclast 1.5L), to hydrolyze the cellulose and xylan components of pretreated corn stover (PCS) was significantly improved by supplementation with three types of crude commercial enzyme preparations nominally enriched in xylanase, pectinase, and beta-glucosidase activity. Although the well-documented relief of product inhibition by beta-glucosidase contributed to the observed improvement in cellulase performance, significant benefits could also be attributed to enzymes components that hydrolyze non-cellulosic polysaccharides. It is suggested that so-called "accessory" enzymes such as xylanase and pectinase stimulate cellulose hydrolysis by removing non-cellulosic polysaccharides that coat cellulose fibers. A high-throughput microassay, in combination with response surface methodology, enabled production of an optimally supplemented enzyme mixture. This mixture allowed for a approximately twofold reduction in the total protein required to reach glucan to glucose and xylan to xylose hydrolysis targets (99% and 88% conversion, respectively), thereby validating this approach towards enzyme improvement and process cost reduction for lignocellulose hydrolysis.