Hydrothermal decomposition of xylan as a model substance for plant biomass waste – Hydrothermolysis in subcritical water

Beech wood xylan, as a model substance for hemicellulose contained in plant biomass waste, was subjected to thermohydrolysis in subcritical water. The composition of the product fractions obtained as a result of its hydrothermal decomposition was studied: the water fraction, the oil fraction and the solid fraction of charred post-reaction residue. An increase in temperature favors xylan thermohydrolysis, leading to the production of saccharides – the products of its hydrolytic depolymerization. The yield of the saccharides contained in the water-soluble product fraction reaches it maximum value at 220 °C and 235 °C, with the retention time of 0 min. Both extending reaction time up to 30 min and further increasing the temperature favor the occurring of secondary reactions – saccharide decomposition – leading to the production, among others, of carboxylic acids, furfurals and aldehydes, and their further carbonization and gasification.     

Extraction and physicochemical characterisation of polysaccharide gum from Yanang (Tiliacora triandra) leaves

Yanang (Tiliacora triandra) is a vegetable used in many cuisines of the northeast of Thailand and Lao People’s Democratic Republic. This paper reports the optimised extraction and some physicochemical characteristics of polysaccharide gum from Yanang leaves. The optimised extraction condition was at the leaf:water ratio of 1:6.6, 85 °C, and 100 min extraction time. The major monosaccharide constituent of Yanang gum was xylose, together with substantial amounts of other neutral sugars. The FT-IR spectra of Yanang gum were similar to that of xylan. Yanang gum exhibited shear-thinning flow behaviour and the extent of shear-thinning was concentration dependent. The mechanical spectra of Yanang gum at low concentration (0.5%) were typical of semi-diluted to concentrated solutions. However, with increasing concentration, the solution behaved like a weak gel.     

The hydrolysis of xylan by Cellulomonas preparations

Thin layer chromatography was demonstrated as an effective technique for observing the time course of hydrolysis of a substituted xylan (arabinoxylan) by crude preparations of Cellulomonas. The chromatograms revealed a sequential pattern of appearance of xylooligomers and arabinoxylooligomers, with early appearance of relatively large oligomers and subsequent accumulation of xylobiose and (to a lesser extent) xylose and arabinose. The pattern indicated that the dominant enzymic activity towards arabinoxylan is that of an endoxylanase.     

A kinetic study of xylose recovery from a hemicellulose-rich biomass for xylitol fermentative production

Hemicellulose in the complex structure of lignocellulosic substances is mainly composed of xylan which is a polymer based on monosaccharide xylose. Using acidic or enzymatic hydrolysis, hemicellulose can be depolymerized into its constituent monomer. The kinetics of hemicellulose depolymerization and decomposition in oat hull was investigated under moderate pressures with catalyst (H₂SO₄) concentration up to 0.55?N and temperatures of up to 130?°C for a total residence time of 150?min. Different trends of recovery or generation and kinetic mechanisms obtained for the components in the hydrolysate which could be described by different kinetic models, that is, a single-phase kinetic mechanism with product decomposition (two-step sequential reaction) could describe xylose generation. However, generation of arabinose, furfural, and acetic acid followed a single-phase mechanism with no decomposition (one-step reaction). Generation of glucose in the hydrolysate followed a biphasic mechanism due to the fast- and slow-releasing fractions into the liquid phase which was apparently with no decomposition. A pentose recovery of almost 80% was achieved under optimal conditions. Parameters of xylitol bioproduction indicated that a xylitol/xylose conversion yield of 0.80?g/g is achievable from the concentrated hydrolysate with no complementary treatment proving its low toxicity compared to other hemicellulose resources.     

Polysaccharides from Sesamum indicum meal: Isolation and structural features

Defatted Sesamum indicum seed cake was extracted, following two separate sequences, and the effects of extraction medium on yield and composition of the extracts were compared. Polysaccharides extracted sequentially with dilute acid and alkali represented 250 mg/g of defatted meal. The isolated polymers contained arabinan, rhamnogalacturonan I (RG I) and arabinogalactan proteins. Polysaccharides extracted during chlorite treatment and with dilute alkali had a higher proportion of rhamnose, suggesting a more branched variety of polymer. Three extracts, which were further characterized by size exclusion chromatography, gave two overlapping peaks. Structural characterisation of hemicellulosic polysaccharides, isolated with KOH, using specific enzyme hydrolysis, ion exchange chromatography (HPAEC) and matrix assisted laser desorption ionisation-time-of-flight (MALDI-TOF) mass spectroscopy, showed that sesame meal xyloglucan (XG) contained XXXG, XXFG and XXLG, and XLLG (named according to Fry et al., 1993) as the major building sub-units in the ratio of 1:0.9:0.3. Hydrolysis with endo-β-(1 → 4)-d-xylanase and analysis of the xylan derived oligosaccharides showed the presence of monomeric xylose (40%), xylobiose (46%) and acidic xylan oligosaccharides containing 4-O-methyl-d-glucuronic acid residues (14%).     

Dilute oxalic acid pretreatment for biorefining giant reed (Arundo donax L.)

Biomass pretreatment is essential to overcome recalcitrance of lignocellulose for ethanol production. In the present study we pretreated giant reed (Arundo donax L.), a perennial, rhizomatous lignocellulosic grass with dilute oxalic acid. The effects of temperature (170-190 °C), acid loading (2-10% w/w) and reaction time (15-40 min) were handled as a single parameter, combined severity. We explored the change in hemicellulose, cellulose and lignin composition following pretreatment and glucan conversion after enzymatic hydrolysis of the solid residue. Two different yeast strains, Scheffersomyces (Pichia) stipitis CBS 6054, which is a native xylose and cellobiose fermenter, and Saccharomyces carlsbergensis FPL-450, which does not ferment xylose or cellobiose, were used along with commercial cellulolytic enzymes in simultaneous saccharification and fermentation (SSF). S. carlsbergensis attained a maximum ethanol concentration of 15.9 g/l after 48 h at pH 5.0, while S. stipitis, at the same condition, took 96 h to reach a similar ethanol value; increasing the pH to 6.0 reduced the S. stipitis lag phase and attained 18.0 g/l of ethanol within 72 h.     

Enhancing the aromatic hydrocarbon yield from the catalytic copyrolysis of xylan and LDPE with a dual-catalytic-stage combined CaO/HZSM-5 catalyst

The high concentration of oxygenated compounds in pyrolytic products prohibits the conversion of hemicellulose to important biofuels and chemicals via fast pyrolysis. Herein CaO and HZSM-5 was developed to convert xylan and LDPE to valuable hydrocarbons by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and elucidate the reaction mechanism were also investigated in detail. The results indicated that xylan/LDPE copyrolysis was more complicated than pyrolysis of the individual components. LDPE hindered the thermal decomposition and aromatic hydrocarbon formation from xylan at temperatures under 350 °C and had a synergistic effect at high temperatures. 50% LDPE was proven to be more beneficial than other percentages for the formation of monocyclic aromatic hydrocarbons. Simultaneously, the addition of CaO/HZSM-5 significantly reduced the reaction Ea and increased the reaction rate. CaO can effectively improve the deoxygenation and aromatization reaction, enhancing the yield and selectivity of aromatics to a certain extent. The maximum yield of hydrocarbons (96.01%), mono-aromatic hydrocarbons (88.53%) and S_BTXE (85.79%) were obtained at a CaO/HZSM-5 ratio of 1:2, a pyrolysis temperature of 450 °C, a catalytic temperature of 550 °C, a catalyst dose of 1:2 and a xylan-to-LDPE ratio of 1:1 via an ex situ process. The system was dominated by toluene, xylene and alkyl benzene. Diels-Alder reactions of furans and hydrocarbon pool mechanism of nonfuranic compounds improved aromatic formation. This study provides a fundamental for recovering energy and chemicals from pyrolysis of hemicellulose.     

Heterologous expression of endo-1,4-beta-xylanaseC from Phanerochaete chrysosporium in Pichia pastoris

The cDNA of endo-1,4-β-xylanaseC, isolated from Phanerochaete chrysosporium, was expressed in Pichia pastoris, under the control of the alcohol oxidase I promoter. Using either the intrinsic leader peptide of xylanaseC or the α-factor signal peptide of Saccharomyces cerevisiae, xylanaseC is efficiently secreted into the medium, at a maximum concentration of 2500 U·l(-1).