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| 2. |
- Berglund, Jennie
(författare)
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Wood Hemicelluloses - Fundamental Insights on Biological and Technical Properties
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hemicelluloses are a group of heterogeneous polysaccharides representing around 30 % of wood where the dominating types are xylans, glucomannans and xyloglucans. Hemicelluloses complex molecular structure makes it difficult to understand the relationship between structure and properties entirely, and their biological role is not yet fully verified. Additionally, hemicelluloses are sensitive to chemical processing and are not utilized to their full potentials for production of value-added products such as materials, additives to food and pharmaceutical products, etc. Increased knowledge regarding their functions is important for the development of both processes and products. The aim with this work has therefore been to increase the fundamental understanding about how the structure and properties of wood hemicelluloses are correlated, and properties such as flexibility, interaction with cellulose, solubility, resistance to chemical-, thermal-, and enzymatic degradation have been explored.Molecular dynamics (MD) simulations were used to, in detail, study the structures found in wood hemicelluloses. The flexibility was evaluated by comparing the impact of backbone sugars on the conformational space and also the impact of side groups was considered. Based on the conformational space of backbone glycosidic linkages the flexibility order of hemicelluloses in an aqueous environment was determined to be: xylan > glucomannan > xyloglucan. Additionally, the impact of xylan structure on cellulose interaction was evaluated by MD methods.Hemicelluloses were extracted from birch and spruce, and were used to fabricate different composite hydrogels with bacterial cellulose. These materials were studied with regards to mechanical properties, and it was shown that galactoglucomannans mainly contributed to an increased modulus in compression, whereas the most significant effect from xylan was increased strain under uniaxial tensile testing. Besides, other polysaccharides of similar structure as galactoglucomannans were modified and used as pure, well defined, models. Acetyl groups are naturally occurring decorations of wood hemicelluloses and can also be chemically introduced. Here, mannans with different degrees of acetylation were prepared and the influence of structure on solubility in water and the organic solvent DMSO were evaluated. Furthermore, the structure and water solubility influenced the interaction with cellulose. Acetylation also showed to increase the thermal and biological stability of mannans.With chemical pulping processes in mind, the degradability of spruce galactoglucomannans in alkaline solution were studied with regards to the structure, and the content of more or less stable structural regions were proposed.
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| 3. |
- Buchert, Johanna, et al.
(författare)
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Effect of pulping and bleaching on pulp carbohydrates and technical properties.
- 1996
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Ingår i: Proceedings Int. Pulp Bleaching. ; , s. 39-42
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Konferensbidrag (refereegranskat)abstract
- Pulping and bleaching have a profound effect on the carbohydrate chem. of kraft pulps. The chem. structure of xylan is modified due to the conversion of methylglucuronic acid side groups to hexenuronic acid side groups. Pulping conditions strongly affect the amt. of hexenuronic acid present in the pulp and subsequently modified kraft pulps have different carboxyl group profiles as compared with conventionally cooked pulps. Due to its reactivity, hexenuronic acid is readily degraded when chlorine dioxide or ozone are used as bleaching chems. However, TCF-pulps bleached with peroxide and oxygen contain high amts. of hexenuronic acid. Thus, depending on the pulping and bleaching method, the quality and quantity of carboxylic acids in different types of pulps varies significantly. The differences in the uronic acid content are in turn reflected in the macroscale properties of the pulps, such as brightness stability.
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| 5. |
- Höije, Anders, 1980, et al.
(författare)
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Material properties of films from enzymatically tailored arabinoxylans
- 2008
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Ingår i: Biomacromolecules. - 1525-7797 .- 1526-4602. ; :9, s. 2042-2047
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Tidskriftsartikel (refereegranskat)abstract
- Rye arabinoxylan with an initial arabinose to xylose (Ara/Xyl) ratio of 0.50 was enzymatically modified with α-L-arabinofuranosidase. Different enzyme dosages were used to prepare arabinoxylan samples with a gradient of arabinose content varying from Ara/Xyl ratio 0.50 to 0.20. The degree of polymerization of the arabinoxylans was not affected by the enzymatic treatment, as detected with SEC-MALLS. Arabinoxylan samples with an Ara/Xyl ratio of 0.30 and below agglomerated in a water solution as seen by changes in light scattering. All samples, however, formed cohesive films upon drying, without addition of external plasticisers. The film from untreated arabinoxylan was completely amorphous; whereas films of the enzyme treated arabinoxylans were semi-crystalline with an increasing degree of crystallinity with decreasing arabinose content as determined by WAXS. Oxygen permeability measurements of the films showed that decreased arabinose content also resulted in lower oxygen permeability of the films. All films were strong and relatively stiff, but showed variations in strain at break. The moderately debranched film with an Ara/Xyl ratio of 0.37 had highest strain at break among all the films tested, yet was stiff and strong. This material also exhibited yielding, and had stress/strain behavior similar to synthetic semi-crystalline polymers, with a tendency to strain induced crystallization. Such combination of mechanical properties combined with oxygen barrier properties is very attractive for packaging applications.
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| 6. |
- Karlsson, Johan, et al.
(författare)
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Enzymatic properties of the low molecular mass endoglucanases Cel12A (EG III) and Cel45A (EG V) of Trichoderma reesei
- 2002
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Ingår i: Journal of Biotechnology. - 1873-4863. ; 99:1, s. 63-78
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Tidskriftsartikel (refereegranskat)abstract
- Trichoderma reesei produces five known endoglucanases. The most studied are Cel7B (EG I) and Cel5A (EG II) which are the most abundant of the endoglucanases. We have performed a characterisation of the enzymatic properties of the less well-studied endoglucanases Cel12A (EG III), Cel45A (EG V) and the catalytic core of Cel45A. For comparison, Cel5A and Cel7B were included in the study. Adsorption studies on microcrystalline cellulose (Avicel) and phosphoric acid swollen cellulose (PASC) showed that Cel5A, Cel7B, Cel45A and Cel45Acore adsorbed to these substrates. In contrast, Cel12A adsorbed weakly to both Avicel and PASC. The products formed on Avicel, PASC and carboxymethylcellulose (CMC) were analysed. Cel7B produced glucose and cellobiose from all substrates. Cel5A and Cel12A also produced cellotriose, in addition to glucose and cellobiose, on the substrates. Cel45A showed a clearly different product pattern by having cellotetraose as the main product, with practically no glucose and cellobiose formation. The kinetic constants were determined on cellotriose, cellotetraose and cellopentaose for the enzymes. Cel12A did not hydrolyse cellotriose. The kCat values for Cel12A on cellotetraose and cellopentaose were significantly lower compared with Cel5A and Cel7B. Cel7B was the only endoglucanase which rapidly hydrolysed cellotriose. Cel45Acore did not show activity on any of the three studied cello-oligosaccharides. The four endoglucanases' capacity to hydrolyse @b-glucan and glucomannan were studied. Cel12A hydrolysed @b-glucan and glucomannan slightly less compared with Cel5A and Cel7B. Cel45A was able to hydrolyse glucomannan significantly more compared with @b-glucan. The capability of Cel45A to hydrolyse glucomannan was higher than that observed for Cel12A, Cel5A and Cel7B. The results indicate that Cel45A is a glucomannanase rather than a strict endoglucanase.
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| 7. |
- Karlsson, Johan, et al.
(författare)
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Homologous expression and characterization of Cel61A (EG IV) of Trichoderma reesei
- 2001
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Ingår i: European Journal of Biochemistry. - : Wiley. - 0014-2956. ; 268:24, s. 6498-6507
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Tidskriftsartikel (refereegranskat)abstract
- There are currently four proteins in family 61 of the glycoside hydrolases, from Trichoderma reesei, Agaricus bisporus, Cryptococcus neoformans and Neurospora crassa. The enzymatic activity of these proteins has not been studied thoroughly. We report here the homologous expression and purification of T. reesei Cel61A [previously named endoglucanase (EG) IV]. The enzyme was expressed in high amounts with a histidine tag on the C-terminus and purified by metal affinity chromatography. This is the first time that a histidine tag has been used as a purification aid in the T. reesei expression system. The enzyme activity was studied on a series of carbohydrate polymers. The only activity exhibited by Cel61A was an endoglucanase activity observed on substrates containing β-1,4 glycosidic bonds, e.g. carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC) and β-glucan. The endoglucanase activity on CMC and β-glucan was determined by viscosity analysis, by measuring the production of reducing ends and by following the degradation of the polymer on a size exclusion chromatography system. The formation of soluble sugars by Cel61A from microcrystalline cellulose (Avicel; Merck), phosphoric acid swollen cellulose (PASC), and CMC were analysed on a HPLC system. Cel61A produced small amounts of oligosaccharides from these substrates. Furthermore, Cel61A showed activity against cellotetraose and cellopentaose. The activity of Cel61A was several orders of magnitude lower compared to Cel7B (previously EG I) of T. reesei on all substrates. One significant difference between Cel61A and Cel7B was that cellotriose was a poor substrate for Cel61A but was readily hydrolysed by Cel7B. The enzyme activity for Cel61A was further studied on a large number of carbohydrate substrates but the enzyme showed no activity towards any of these substrates.
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| 8. |
- Kisonen, Victor, et al.
(författare)
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Composite films of nanofibrillated cellulose and O-acetyl galactoglucomannan (GGM) coated with succinic esters of GGM showing potential as barrier material in food packaging
- 2015
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 50:8, s. 3189-3199
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Tidskriftsartikel (refereegranskat)abstract
- Nanofibrillated cellulose (NFC)-Norway spruce O-acetyl-galactoglucomannan (GGM) composite films were coated either with a novel succinic ester of GGM or with native GGM. NFC films were made for reference. The succinic ester of GGM was synthesised at low (GGM-Su1) and high (GGM-Su2) degree of substitution to obtain different level of water repellence. GGM and its succinic esters had good affinity with NFC substrate. This made it possible to implement the barrier functionality on the NFC network with the adequate mechanical properties. The coatings further enhanced the already excellent oxygen permeability properties, achieving 0.1 [(cm(3) A mu m)(m(2) kPa d)] as the lowest value with the NFC-GGM film double-coated with GGM-Su2. The films demonstrated pronounced stiffness by adding GGM to the NFC, as well as coating of GGM-Su2 on the NFC-GGM films at 0-90 % relative humidity. The films turned out to be impenetrable with grease even at high temperatures. NFC-GGM film with GGM-Su2 coating exhibited hydrophobic characteristics according to the water contact angle measurements. It was shown that adding 5.5 wt% of GGM to a NFC film and further 5.4 wt% of coating of GGM-Su or GGM on the film may highly enhance the feasibility of the biocomposites to be used for food packaging to replace typical oil-based non-biodegradable plastics currently used.
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| 9. |
- Kotiranta, Pia, et al.
(författare)
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Adsorption and Activity of Trichoderma reesei Cellobiohydrolase I, Endoglucanase II, and the Corresponding Core Proteins on Steam Pretreated Willow
- 1999
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Ingår i: Applied Biochemistry and Biotechnology. - 1559-0291. ; 81:2, s. 81-90
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption and the hydrolytic action of purified cellulases of Trichoderma reesei, namely, cellobiohydrolase I (CBH I), endoglucanase II (EG II), and their core proteins, on steam-pretreated willow were compared. The two enzymes differed clearly in their adsorption and hydrolytic behavior. CBH I required the cellulose-binding domain (CBD) for efficient adsorption and hydrolysis, whereas EG II was able to adsorb to steam pretreated willow without its CBD. Absence of the CBD decreased the hydrolysis of cellulose by EG II, but the decrease was less pronounced than with CBH I. A linear relationship was observed between the amount of enzyme adsorbed and the degree of hydrolysis of cellulose only for CBH I. EG II and EG II core appeared to be able to hydrolyze only 1 to 2% of the substrate regardless of the amount of protein adsorbed.
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| 10. |
- Leppänen, Ann-Sofie, et al.
(författare)
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Targeted allylation and propargylation of galactose-containing polysaccharides in water
- 2014
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 100, s. 46-54
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Tidskriftsartikel (refereegranskat)abstract
- Galactose units of spruce galactoglucomannan (GGM), guar galactomannan (GM), and tamarind (galacto)xyloglucan (XG) were selectively allylated. Firstly aldehyde functionalities were formed at the C-6 position via enzymatic oxidation by galactose oxidase. The formed aldehydes were further derivatized by an indium mediated Barbier-Grignard type reaction, resulting in the formation of homoallylic alcohols. In addition to allylic halides, the same reaction procedure was also applicable for GGM, when using propargyl bromide as halide. All reaction steps were done in water, thus the polysaccharides were modified in a one-pot reaction. The formation of the allylated, or propargylated, product was identified by MALDI-TOF-MS. All polysaccharide products were isolated and further characterized by GC-MS or NMR spectroscopy. By this chemo-enzymatic process, we have demonstrated a novel method for derivatization of GGM and other galactose-containing polysaccharides. The derivatized polysaccharides are potential platforms for further functionalizations.
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