Showing papers on "Hemicellulose published in 2005"

Xylanases from fungi: properties and industrial applications

Abstract: Xylan is the principal type of hemicellulose. It is a linear polymer of beta-D-xylopyranosyl units linked by (1-4) glycosidic bonds. In nature, the polysaccharide backbone may be added to 4-O-methyl-alpha-D-glucuronopyranosyl units, acetyl groups, alpha-L-arabinofuranosyl, etc., in variable proportions. An enzymatic complex is responsible for the hydrolysis of xylan, but the main enzymes involved are endo-1,4-beta-xylanase and beta-xylosidase. These enzymes are produced by fungi, bacteria, yeast, marine algae, protozoans, snails, crustaceans, insect, seeds, etc., but the principal commercial source is filamentous fungi. Recently, there has been much industrial interest in xylan and its hydrolytic enzymatic complex, as a supplement in animal feed, for the manufacture of bread, food and drinks, textiles, bleaching of cellulose pulp, ethanol and xylitol production. This review describes some properties of xylan and its metabolism, as well as the biochemical properties of xylanases and their commercial applications.

Biorefining of softwoods using ethanol organosolv pulping: preliminary evaluation of process streams for manufacture of fuel-grade ethanol and co-products.

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 (≤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. © 2005 Wiley Periodicals, Inc.

Understanding factors that limit enzymatic hydrolysis of biomass: characterization of pretreated corn stover.

Abstract: Spectroscopic characterization of both untreated and treated material is being performed in order to determine changes in the biomass and the effects of pretreatment on crystallinity, lignin content, selected chemical bonds, and depolymerization of hemicellulose and lignin. The methods used are X-ray diffraction for determination of cellulose crystallinity (CrI); diffusive reflectance infrared (DRIFT) for changes in C-C and C-O bonds; and fluorescence to determine lignin content. Changes in spectral characteristics and crystallinity are statistically correlated with enzymatic hydrolysis results to identify and better understand the fundamental features of biomass that govern its enzymatic conversion to monomeric sugars. Models of the hydrolysis initial rate and 72 h extent of conversion were developed and evaluated. Results show that the hydrolysis initial rate is most influenced by the cellulose crystallinity, while lignin content most influences the extent of hydrolysis at 72 h. However, it should be noted that in this study only crystallinity, lignin, and selected chemical bonds were used as inputs to the models. The incorporation of additional parameters that affect the hydrolysis, like pore volume and size and surface area accessibility, would improve the predictive capability of the models.

Understanding factors that limit enzymatic hydrolysis of biomass

Abstract: Spectroscopic characterization of both untreated and treated material is being performed in order to determine changes in the biomass and the effects of pretreatment on crystallinity, lignin content, selected chemical bonds, and depolymerization of hemicellulose and lignin. The methods used are X-ray diffraction for determination of cellulose crystallinity (CrI); diffusive reflectance infrared (DRIFT) for changes in C-C and C-O bonds; and fluorescence to determine lignin content. Changes in spectral characteristics and crystallinity are statistically correlated with enzymatic hydrolysis results to identify and better understand the fundamental features of biomass that govern its enzymatic conversion to monomeric sugars. Models of the hydrolysis initial rate and 72 h extent of conversion were developed and evaluated. Results show that the hydrolysis initial rate is most influenced by the cellulose crystallinity, while lignin content most influences the extent of hydrolysis at 72 h. However, it should be noted that in this study only crystallinity, lignin, and selected chemical bonds were used as inputs to the models. The incorporation of additional parameters that affect the hydrolysis, like pore volume and size and surface area accessibility, would improve the predictive capability of the models.

Extraction and characterization of original lignin and hemicelluloses from wheat straw.

Abstract: Original lignin and hemicelluloses were sequentially extracted with high yield/purity, using acidic dioxane/water solution and dimethyl sulfoxide, from ball-milled wheat straw. The acidic dioxane lignin fraction is distinguished by high beta-O-4' structures and by low amounts of condensed units (beta-5', 5-5', and beta-1'). Hemicelluloses contain arabinoxylans as the major polysaccharides, which are substituted by alpha-l-arabinofuranose, 4-O-methylglucuronic acid, acetyl group (DS = 0.1), and xylose at O-3 and/or O-2 of xylans. It was found that arabinoxylans form cross-links with lignins through ferulates via ether bonds, glucuronic acid via ester bonds, and arbinose/xylose via both ether and glycosidic bonds, respectively, in the cell walls of wheat straw. Diferulates are also incorporated into cross-links between lignin and hemicelluloses as well as lignification of wheat straw cell walls. The guaiacyl unit is considered to be a significant condensed structural constructor in extracted lignin and a connector between lignin and carbohydrates.

Acid hydrolysis and fermentation of brewer's spent grain to produce xylitol

Abstract: The hemicellulosic fraction of brewer's spent grain (BSG) was hydrolysed with diluted acid under different conditions of liquid/solid ratio (8–12 g g−1), sulfuric acid concentration (100–140 mg g−1 dry matter) and reaction time (17–37 min) in order to produce a liquor with a large amount of xylose and good fermentability to produce xylitol. Results showed that all the evaluated reaction conditions were able to hydrolyse xylan and arabinan with efficiencies higher than 85.8 and 95.7% respectively, and even under the mildest reaction condition a considerable amount (92.7%) of the hemicellulosic fraction could be extracted. The hydrolysates presented different fermentabilities when used as fermentation media for xylitol production by Candida guilliermondii yeast, owing to the differences in their composition. Based on statistical analysis, the best condition for BSG acid hydrolysis was the use of a liquid/solid ratio of 8 g g−1, 100 mg H2SO4 g−1 dry matter and a reaction time of 17 min. Under this condition a high extraction efficiency of hemicellulosic sugars (92.7%) and good fermentation results (YP/S = 0.70 g g−1 and QP = 0.45 g dm−3 h−1) were attained. Copyright © 2005 Society of Chemical Industry

Determination of total carbohydrates

Abstract: Plant cell walls are an intricate composite matrix consisting largely of lignin, a phenolic-derived polymer, and the structural carbohydrates, primarily cellulose and hemicelluloses. In addition, minor amounts of pectin and protein are also present, but only represent a small fraction to the secondary xylem of plants, which forms the bulk of terrestrial plant biomass and provides a substrate for litter-degrading microorganisms. Several approaches have been developed to quantify cell wall constituents. This chapter describes two analytical procedures to accurately measure total cell wall carbohydrates. Plant litter is ground in liquid nitrogen and hydrolysed in 72% H2SO4. This secondary acid hydrolysis converts the polymeric carbohydrates to their monomeric fractions, which can be separated, identified and quantified by high performance anion exchange liquid chromatography (HPAELC) with water as the mobile phase and electrochemical or refractive index detection. Alternatively, the monomers are derivatised by acetylation and separated, identified and quantified by gas chromatography (GC) with helium as carrier gas and flame ionisation detection (FID). Both chromatographic methods have been successfully applied to various types of litter originating from diverse environments and representing different degrees of decomposition.

High-performance composites from low-cost plant primary cell walls

Abstract: Our aim was to develop means to produce purified cellulose cell wall fragments and cellulose microfibrils from primary cellular material at laboratory scale, to form novel composite materials with a range of matrix binders and to determine their tensile properties. Swede root was processed to produce cell wall fragments. Separation of microfibrils from the fragments of the cellulose wall ‘skeleton’ was achieved using a severe shear treatment provided by a high-pressure food homogeniser. Composites with four types of matrix material were formed from the wet state cellulose. For composites made with purified cell wall fragments (PCWF), an acrylic matrix gave the best strength (125 MPa) while the best stiffness was produced by PCWF and PVA (15.32 GPa). The best performance from the fibrilised cell wall material (FCWM) was obtained with PVA (tensile strength 145 MPa and tensile modulus 8.9 GPa). Cellulose composites made using a plant-derived hemicellulose matrix gave tensile strength 100 MPa and tensile modulus 6.0 GPa. These performances are within the range of chopped strand mat glass fibre and polyester composites. Feasibility of extraction and application in composite form has been demonstrated.

Simultaneous Saccharification and Co-Fermentation of Crystalline Cellulose and Sugar Cane Bagasse Hemicellulose Hydrolysate to Lactate by a Thermotolerant Acidophilic Bacillus sp.

Abstract: Polylactides produced from renewable feedstocks, such as corn starch, are being developed as alternatives to plastics derived from petroleum. In addition to corn, other less expensive biomass resources can be readily converted to component sugars (glucose, xylose, etc.) by enzyme and/or chemical treatment for fermentation to optically pure lactic acid to reduce the cost of lactic acid. Lactic acid bacteria used by the industry lack the ability to ferment pentoses (hemicellulose-derived xylose and arabinose), and their growth and fermentation optima also differ from the optimal conditions for the activity of fungal cellulases required for depolymerization of cellulose. To reduce the overall cost of simultaneous saccharification and fermentation (SSF) of cellulose, we have isolated bacterial biocatalysts that can grow and ferment all sugars in the biomass at conditions that are also optimal for fungal cellulases. SSF of Solka Floc cellulose by one such isolate, Bacillus sp. strain 36D1, yielded l(+)-lactic acid at an optical purity higher than 95% with cellulase (Spezyme CE; Genencor International) added at about 10 FPU/g cellulose, with a product yield of about 90% of the expected maximum. Volumetric productivity of SSF to lactic acid was optimal between culture pH values of 4.5 and 5.5 at 50 degrees C. At a constant pH of 5.0, volumetric productivity of lactic acid was maximal at 55 degrees C. Strain 36D1 also co-fermented cellulose-derived glucose and sugar cane bagasse hemicellulose-derived xylose simultaneously (SSCF). In a batch SSCF of 40% acid-treated hemicellulose hydrolysate (over-limed) and 20 g/L Solka Floc cellulose, strain 36D1 produced about 35 g/L lactic acid in about 144 h with 15 FPU of Spezyme CE/g cellulose. The maximum volumetric productivity of lactic acid in this SSCF was 6.7 mmol/L (h). Cellulose-derived lactic acid contributed to about 30% of this total lactic acid. These results show that Bacillus sp. strain 36D1 is well-suited for simultaneous saccharification and co-fermentation of all of the biomass-derived sugars to lactic acid.

Optimization of Dilute-Acid Pretreatment of Corn Stover Using a High-Solids Percolation Reactor

Abstract: We have previously demonstrated that pretreatment of corn stover with dilute sulfuric acid can achieve high digestibility and efficient recovery of hemicellulose sugars with high yield and concentration. Further improvement of this process was sought in this work. A modification was made in the operation of the percolation reactor that the reactor is preheated under atmospheric pressure to remove moisture that causes autohydrolysis. This eliminated sugar decomposition during the preheating stage and led to a considerable improvement in overall sugar yield. In addition, liquid throughput was minimized to the extent that only one reactor void volume of liquid was collected. This was done to attain a high xylose concentration in the hydrolyzate. The optimum reaction and operating conditions were identified wherein near quantitative enzymatic digestibilities are obtained with enzyme loading of 15 FPU/g glucan. With a reduced enzyme loading of 5 FPU/g glucan, the enzymatic digestibility was decreased, but still reached a level of 92%. Decomposition of carbohydrates was extremely low as indicated by the measured glucan and xylan mass closures (recovered sugar plus unreacted) which were 98% and 94%, respectively. The data obtained in this work indicate that the digestibility is related to the extent of xylan removal.

Obtaining carbon nanotubes from grass

Abstract: Multi-walled carbon nanotubes (MCNTs) can be obtained by heating grass in the presence of a suitable amount of oxygen. Grass contains a large amount of vascular bundles in the stem and nervation. The major compositions of them are cellulose, hemicellulose and lignin. In the present approach, a rapid heat treatment (at about 600 °C) and the participation of oxygen make the vascular bundles become dehydrated and turn into carbon nanotubes. The diameters of the carbon nanotubes obtained are between 30 and 50 nm.

Evaluation of wheat stillage for ethanol production by recombinant Zymomonas mobilis

Abstract: Stillage is the main residue from the starch-to-ethanol fermentation process. Carbohydrates (hemicellulose and cellulose) comprise approximately 50% (w/w) of the total components of stillage. Conversion of the hemicellulose and cellulose to fermentable sugars and then to ethanol has the potential to significantly increase the efficiency of the process. The hydrolysis of stillage to fermentable sugars was optimised using 2% (v/v) H 2 SO 4 at 100 ∘ C for 5.5 h and produced 18 g/L xylose, 11.5 g/L arabinose and 6.5 g/L glucose from 120 g/L stillage. Further hydrolysis using enzymes increased the release of glucose by 61%. Furfural, acetate and lactate were the main inhibitors present in the acid hydrolysate of stillage. The lignin-derived inhibitors hydroxymethylfuraldehyde, hydroxybenzaldehyde, vanillin and syringaldehyde were not detected. Neutralisation of the hydrolysate with lime to pH 5 decreased the concentration of furfural by 50%. Fermentation of hydrolysate supplemented with glucose 10 g/L, by recombinant Zymomonas mobilis ZM4(pZB5), produced 11 g/L of ethanol after 70 h, with residual xylose 12 g/L. Supplementation of the hydrolysate with 5 g/L yeast extract and 40 g/L glucose produced 28 g/L ethanol with 2.6 g/L residual xylose after 18 h. Arabinose was not utilised by this particular recombinant strain. From the results, Z. mobilis ZM4(pZB5) may be a suitable candidate for the fermentation of both glucose and xylose in stillage acid hydrolysates.

Cultivation of mushroom (Volvariella volvacea) on banana leaves.

Abstract: Following the solid state fermentation of banana leaves (Musa sapientum lina) by lignin degrading mushroom (Volvariella volvacea), yield of fruiting bodies and compositional changes of the substrate were evaluated using a student parametric “T” test model. The biological efficiency was 5.21 while the total weight of fruit yield was 2.5 kg. The percentage biomass loss was 18.20%. The banana leaves treated with V. volvacea exhibited losses primarily in the polysaccharide components and with a greater percentage of the fibre components being degraded. The crude protein content was enhanced by the incubation of the mushroom due probably to the addition of microbial protein. The acid detergent lignin (ADL) was significantly reduced in the fungus treated sample. The acid detergent fibre (ADF) and neutral detergent fibre (NDF) followed similar trend but, the cellulose and hemicellulose increased. The development of this simple technology is expected to improve the yield of mushroom as well as provide sustainable feed (spent substrate) for ruminant animals.

Thermogravimetric analysis of composites obtained from sintering of rice husk-scrap tire mixtures

Abstract: The disposal of used automotive tires has caused many environmental and economical problems to most countries. We propose the use of rice husk as filler for increasing the value of recycled tire rubber. Thermal degradation of both components and their sintering mixtures is presented in this paper. Thermal decomposition of rice husk occurs in various steps in the temperature range between 150 and 550°C. This complex process is the result of the overlapping of thermal decomposition of the three major constituents common in all lignocellulosic materials, i.e., hemicellulose, lignin and cellulose. Hemicellulose is degraded at temperatures between 150 and 350°C, cellulose from 275 to 380°C and lignin from 250 to 550°C. The degradation process of major constituents of scrap tires or their composites is observed at temperatures between 150 and 550°C. For composites, the addition of rice husk (maximum 25%) produces an increase in the mass loss rate. This effect is higher as the amount of rice husk increases. However, the degradation initial temperature of elastomeric matrix is not affected with addition of rice husk. Apparent kinetic parameters were also studied by the isoconversional Friedman method. We observed that the addition of rice husk produces a decrease in apparent activation energy for low conversions (up to 0.6). For higher conversions this decrease was not so clearly observed.

Effects of Hemicellulose and Lignin on Enzymatic Hydrolysis of Cellulose from Dairy Manure

Abstract: This study focused on the effect of hemicellulose and lignin on enzymatic hydrolysis of dairy manure and hydrolysis process optimization to improve sugar yield. It was found that hemicellulose and lignin in dairy manure, similar to their role in other lignocellulosic material, were major resistive factors to enzymatic hydrolysis and that the removal of either of them, or for best performance, both of them, improved the enzymatic hydrolysis of manure cellulose. This result combined with scanning electron microscope (SEM) pictures further proved that the accessibility of cellulose to cellulase was the most important feature to the hydrolysis. Quantitatively, fed-batch enzymatic hydrolysis of fiber without lignin and hemicellulose had a high glucose yield of 52% with respect to the glucose concentration of 17 g/L at a total enzyme loading of 1300 FPU/L and reaction time of 160 h, which was better than corresponding batch enzymatic hydrolysis.