Oligosaccharides obtained by enzymatic hydrolysis of birch kraft pulp xylan: analysis by capillary zone electrophoresis and mass spectrometry

Analysis of monosaccharides and oligosaccharides in the pulp and paper industry by use of capillary zone electrophoresis: a review

Carbohydrate analysis is an important source of the information required for understanding and control of pulp and paper processes. The behavior of cellulose and hemicelluloses in the process, carbohydrate-lignin interactions, and the enzymatic treatment of fibers are examples of situations for which reliable, fast, qualitative, and quantitative methods are required. New uses of lignocellulosic material have further increased the need for carbohydrate analysis. This review collates and summarizes the most important findings and approaches in the analysis of wood-based carbohydrates by use of capillary zone electrophoresis and provides an analysis of the effect of different conditions on the separation, showing the advantages and limitations of the methods used. It provides guidelines for achieving higher quality and improved separation efficiency in carbohydrate analysis.

Enzyme-aided alkaline extraction of oligosaccharides and polymeric xylan from hardwood kraft pulp

In this paper we describe the effect of enzyme treatments on the production of polymeric xylan, oligosaccharides and hemicellulose lean pulp by alkaline extraction of bleached hardwood kraft pulp. Enzyme treatments were carried out before one or in between two subsequent alkaline extractions by purified Trichoderma reesei xylanase and endoglucanase II (Cel 5a) as well as by a commercial monocomponent endoglucanase (FibreCareR). Without enzyme pre-treatment 61% and 7% of the pulp xylan was extracted in high purity in the first and second alkaline stage, respectively. Higher molecular mass xylan was obtained in the second than in the first alkaline extraction. Xylanase treatment before alkaline extraction hydrolyzed up to 12% of xylan to xylooligosaccharides. According to our results, preparation of polymeric xylan, and/or oligosaccharides as well as hemicellulose lean pulp with cellulose content of 93-94%, is possible by enzyme-aided alkaline extraction process.

Xylan and Xylan Derivatives – Basis of Functional Polymers for the Future

This review highlights xylan and xylan derivatives. It depicts the occurrence and structural diversity of the biopolymer, followed by a presentation of different ways of isolation from biomass. The determination of characteristics, i.e., molecular weight, interaction with other polysaccharides, thermal behaviour, and the biological activity of xylan are reviewed. The application potential arising from the structural features of the unmodified xylan is pointed out. Special attention is concentrated on the possibilities of the modification of functional properties by chemical functionalization of the biopolymers in order to design advanced materials. Within this review recent results in the field are accompanied with selected results of our own work.

Optimization of CZE for analysis of phytochemical bioactive compounds

Advantages of CZE such as high efficiency, low cost, short analysis time, and easy implementation result in its wide applications for analysis of phytochemical bioactive compounds (e.g. flavonoids, alkaloids, terpenoids, phenolic acid, saponins, anthraquinones and coumarins). However, several aspects, including sample preparation, separation, and detection have significant effects on CZE analysis. Therefore, optimization of these procedures is necessary for development of the method. In this review, sample preparation such as extraction method and preconcentration, separation factors including buffer type, concentration and pH, additives, voltage and temperature, as well as detection, e.g. direct and indirect UV detection, LIF and MS were discussed for optimization of CZE analysis on phytochemical bioactive compounds. The optimized strategies were also reviewed.

Characterization of XynC from Bacillus subtilis subsp. subtilis strain 168 and analysis of its role in depolymerization of glucuronoxylan

Secretion of xylanase activities by Bacillus subtilis 168 supports the development of this well-defined genetic system for conversion of methylglucuronoxylan (MeGAXn [where n represents the number of xylose residues]) in the hemicellulose component of lignocellulosics to biobased products. In addition to the characterized glycosyl hydrolase family 11 (GH 11) endoxylanase designated XynA, B. subtilis 168 secretes a second endoxylanase as the translated product of the ynfF gene. This sequence shows remarkable homology to the GH 5 endoxylanase secreted by strains of Erwinia chrysanthemi. To determine its properties and potential role in the depolymerization of MeGAXn, the ynfF gene was cloned and overexpressed to provide an endoxylanase, designated XynC, which was characterized with respect to substrate preference, kinetic properties, and product formation. With different sources of MeGAXn as the substrate, the specific activity increased with increasing methylglucuronosyl substitutions on the beta-1,4-xylan chain. With MeGAXn from sweetgum as a preferred substrate, XynC exhibited a Vmax of 59.9 units/mg XynC, a Km of 1.63 mg MeGAXn/ml, and a k(cat) of 2,635/minute at pH 6.0 and 37 degrees C. Matrix-assisted laser desorption ionization-time of flight mass spectrometry and 1H nuclear magnetic resonance data revealed that each hydrolysis product has a single glucuronosyl substitution penultimate to the reducing terminal xylose. This detailed analysis of XynC from B. subtilis 168 defines the unique depolymerization process catalyzed by the GH 5 endoxylanases. Based upon product analysis, B. subtilis 168 secretes both XynA and XynC. Expression of xynA was subject to MeGAXn induction; xynC expression was constitutive with growth on different substrates. Translation and secretion of both GH 11 and GH 5 endoxylanases by the fully sequenced and genetically malleable B. subtilis 168 recommends this bacterium for the introduction of genes required for the complete utilization of products of the enzyme-catalyzed depolymerization of MeGAXn. B. subtilis may serve as a model platform for development of gram-positive biocatalysts for conversion of lignocellulosic materials to renewable fuels and chemicals.

Analysis of chitin oligosaccharides by capillary electrophoresis with laser-induced fluorescence

A method, using capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection for analyzing chitin oligosaccharides is described. Chitin oligosaccharides were derivatized with 9-aminopyrene-1,4,6-trisulfonate (APTS) via reductive amination at 37 degrees C for 16 h (optimized conditions). The APTS-chitin oligosaccharides were analyzed using either an acidic citric acid-phosphate buffer or an alkaline borate buffer. The effects of buffer types, buffer pH values, and buffer concentrations on the separation were examined. The analytes were successfully separated by using a pH 4.6 citric acid-phosphate within 19 min. The APTS-derivatized chitin monosaccharide (D-glucosamine) migrated first. The analytes were also completely separated by using a pH 9.0 borate buffer within 24 min. Moreover, the specificity of enzyme digestion on chitin polysaccharides using the optimized APTS labeling procedure and the CE-LIF method was demonstrated.

Capillary zone electrophoresis of syringyl and guaiacyl monomers resulting from lignin thioacidolysis

A capillary zone electrophoretic method has been developed for the quantitative determination of syringyl (S) and guaiacyl (G) monomers resulting from lignin thioacidolysis. The effects on the separation of altering a number of parameters have been investigated, resulting in an efficient and rapid separation. Analysis times were about 10 min instead of 50 min for the conventional GC methods, with no requirement for a derivatisation step prior to analysis. Relative standard deviations ranged between 8 and 12% for the absolute determination of S and G monomers, and between 1.4 and 3.5% for the S/G ratio.

Functional characterization of a novel xylanase from a corn strain of Erwinia chrysanthemi

A beta-1,4-xylan hydrolase (xylanase A) produced by Erwinia chrysanthemi D1 isolated from corn was analyzed with respect to its secondary structure and enzymatic function. The pH and temperature optima for the enzyme were found to be pH 6.0 and 35 degrees C, with a secondary structure under those conditions that consists of approximately 10 to 15% alpha-helices. The enzyme was still active at temperatures higher than 40 degrees C and at pHs of up to 9.0. The loss of enzymatic activity at temperatures above 45 degrees C was accompanied by significant loss of secondary structure. The enzyme was most active on xylan substrates with low ratios of xylose to 4-O-methyl-D-glucuronic acid and appears to require two 4-O-methyl-D-glucuronic acid residues for substrate recognition and/or cleavage of a beta-1,4-xylosidic bond. The enzyme hydrolyzed sweetgum xylan, generating products with a 4-O-methyl-glucuronic acid-substituted xylose residue one position from the nonreducing terminus of the oligoxyloside product. No internal cleavages of the xylan backbone between substituted xylose residues were observed, giving the enzyme a unique mode of action in the hydrolysis compared to all other xylanases that have been described. Given the size of the oligoxyloside products generated by the enzyme during depolymerization of xylan substrates, the function of the enzyme may be to render substrate available for other depolymerizing enzymes instead of producing oligoxylosides for cellular metabolism and may serve to produce elicitors during the initiation of the infectious process.

Enhancement of the quality of MALDI mass spectra of highly acidic oligosaccharides by using a nafion-coated probe

Spectra of highly acidic oligosaccharides obtained by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) can be greatly enhanced in quality by coating the MALDI probe surface with a film consisting of a perfluorosulfonated ionomer (Nafion) prior to the addition of the sample-matrix mixture. For comparison, three mixtures containing highly acidic oligo- and polysaccharides derived from partial acidic hydrolysis of alginate, pectin, or carboxymethyl cellulose (CMC) were analyzed by employing probes with an uncoated gold surface or a surface coated with a Nafion or nitrocellulose film. The negative ion-mode MALDI spectra of the oligouronates (oligomers containing mannuronic/guluronic and galacturonic acid residues) obtained using uncoated or nitrocellulose-coated probes consisted of a series of broad, multiple peaks. These multiple peaks were assigned to the molecular ions of the nondissociated [M - H]- and partially sodiated [MnNa - H]-, where n = 1, 2, or 3, oligomers. In contrast, the corresponding spectra obtained with Nafion-coated probes contained only a single series of sharp peaks originating from the molecular ions ([M - H]-) of nondissociated oligomers exhibiting chain lengths of as many as approximately 15 uronic acid residues. The Nafion coating was apparently capable of removing the sodium counterions remaining in the deposit of the sample-matrix mixture on the probe, thereby greatly enhancing the signal-to-noise ratios of the peaks in the spectra. In a similar manner, higher quality spectra could also be obtained by using Nafion-coated probes for analysis of the oligouronates and CMC oligomers by positive ion-mode MALDI-MS.

Analysis of carbohydrates in wood and pulps employing enzymatic hydrolysis and subsequent capillary zone electrophoresis

An efficient method for determining the carbohydrate composition of extractive-free delignified wood and pulp is described here. The polysaccharides in the sample are first hydrolyzed using a mixture of commercially available preparations of cellulase and hemicellulase. The reducing saccharides in the hydrolysate thus obtained are subsequently derivatized with 4-aminobenzoic acid ethyl ester and thereafter quantitated by capillary zone electrophoresis (CZE) in an alkaline borate buffer with monitoring of the absorption at 306 nm. All reducing sugars (i.e., neutral monosaccharides and uronic acids) which occur as structural elements in the polysaccharides of wood and pulp can be quantitated in a single such analytical run, which can also determine the contents of 4-deoxy-beta-L-threo-hex-4-enopyranosyluronic acid (HexA) residues present in pulps obtained from alkaline processes. CZE analyses were performed using linear regression of standard curves over a concentration range spanning approximately three orders of magnitude. Carbohydrate constituents constituting approximately 0.1% of the dry mass of the sample could be quantitated. The overall precision of this analytical procedure--involving enzymatic hydrolysis, derivatization and CZE--was good (RSD=2.2-7.5%), especially considering the heterogeneity of the wood and pulp samples. The total yield of carbohydrates (93-97%) obtained employing the procedure developed here was consistently higher than that obtained upon applying the traditional procedure for carbohydrate analysis (85-93%) (involving acid hydrolysis and gas chromatographic analysis) to the same pulps. The trisaccharide HexA-xylobiose was the only HexA-containing saccharide detected using the conditions for enzymatic hydrolysis developed here (i.e., 30 h incubation at pH 4 and 40 degrees C); whereas mixtures of HexA-xylobiose and HexA-xylotriose were obtained when the incubation was performed at pH 5 or 6.

Matrix-assisted laser desorption/ionization mass spectrometry of carbohydrates

This review describes the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to carbohydrate analysis and covers the period 1991-1998. The technique is particularly valuable for carbohydrates because it enables underivatised, as well as derivatised compounds to be examined. The various MALDI matrices that have been used for carbohydrate analysis are described, and the use of derivatization for improving mass spectral detection limits is also discussed. Methods for sample preparation and for extracting carbohydrates from biological media prior to mass spectrometric analysis are compared with emphasis on highly sensitive mass spectrometric methods. Quantitative aspects of MALDI are covered with respect to the relationship between signal strength and both mass and compound structure. The value of mass measurements by MALDI to provide a carbohydrate composition is stressed, together with the ability of the technique to provide fragmentation spectra. The use of in-source and post-source decay and collision-induced fragmentation in this context is described with emphasis on ions that provide information on the linkage and branching patterns of carbohydrates. The use of MALDI mass spectrometry, linked with exoglycosidase sequencing, is described for N-linked glycans derived from glycoproteins, and methods for the analysis of O-linked glycans are also covered. The review ends with a description of various applications of the technique to carbohydrates found as constituents of glycoproteins, bacterial glycolipids, sphingolipids, and glycolipid anchors.

Structure of neutral branched xylooligosaccharides produced by xylanase from in situ reduced hardwood xylan

Two neutral oligosaccharides from in situ reduced hardwood xylan were isolated and completely characterized by methylation analysis and 2D NMR spectroscopy (COSY, HOHAHA, HMQC, HMQC-TOCSY, NOESY, and HMBC techniques). The oligosaccharides are the xylotetrasaccharide, 4-O-methyl-alpha-D-glucopyranosyl-(1-->2)-D-xylotriose and the xylopentasaccharide 4-O-methyl-alpha-D-glucopyranosyl-(1-->2)-D-xylotetraose. From reactivities observed with these compounds, the mode of action of beta-xylanase is described.