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Wood Hemicelluloses - Fundamental Insights on Biological and Technical Properties
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Wood Chemistry and Pulp Technology. Wallenberg Wood Science Center.ORCID iD: 0000-0003-0277-2269
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Abstract [sv]

Hemicellulosor är en grupp av heterogena polysackarider som utgör ca 30 % av trä och där de vanligaste typerna är xylaner, glukomannaner och xyloglukaner. Den komplexa strukturen gör det svårt att fullständigt förstå förhållandet mellan struktur och egenskaper, och deras biologiska roll är ännu inte fullständigt kartlagd. Dessutom är hemicellulosor känsliga för kemiska processer och tas inte tillvara på bästa sätt för att tillverka förädlade produkter så som nya material eller användas som additiv till livsmedel och farmaceutiska produkter etc. En ökad kunskap om deras funktion är viktig för utvecklingen av både processer och material. Målet med detta arbete har därför varit att öka den fundamentala förståelsen för hur struktur och egenskaper hos hemicellulosor från trä hänger ihop. Egenskaper så som flexibilitet, interaktion med cellulosa, löslighet, samt kemisk-, termisk- och biologisk stabilitet har utvärderats.

Molekyldynamiska (MD) simuleringar användes för att studera strukturer som återfinns i hemicellulosor på detaljnivå. Flexibiliteten utvärderades med avseende på hur konformationsrymden påverkades av vilka monosackarider som ingick i huvudkedjan, samt påverkan från sidogrupper. Baserat på huvudkedjan bör flexibilitetsordningen för studerade hemicellulosor i vattenlösning vara: xylan > glukomannan > xyloglukan. Dessutom användes MD simuleringar för att analysera hur strukturen hos xylaner påverkar interaktionen med cellulosa.

Hemicellulosor extraherades från björk och gran, och användes för att producera flera olika komposithydrogeler med bakteriell cellulosa. Dessa material studerades bland annat med avseende på de mekaniska egenskaperna och de tydligaste observationerna var att galaktoglukomannan bidrog till en ökad kompressionsmodul, medan xylan framförallt ökade töjbarheten i dragprov. Dessutom modifierades modellpolysackarider med liknande struktur som galaktoglukomannan och användes som extra rena och väldefinierade modellsystem. Acetylgrupper förekommer naturligt som sidogrupper på hemicellulosor och de kan även introduceras via kemisk modifiering. I detta projekt tillverkades mannaner med olika acetyleringsgrad och hur strukturen påverkade lösligheten i vatten och det organiska lösningsmedlet DMSO utvärderades. Det visade sig även att strukturen och lösligheten i vatten påverkade interaktionen med cellulosa. Acetyleringen hade också en positiv effekt på den biologiska och termiska stabiliteten.

Med kemiska massaprocesser i åtanke studerades nedbrytbarheten hos galaktoglukomannaner från gran i alkalisk lösning med avseende på strukturen och förekomsten av mer eller mindre stabila strukturella regioner föreslogs.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2018. , p. 82
Series
TRITA-CBH-FOU ; 2018:63
Keywords [en]
hemicellulose, wood, glucomannan, xylan, structure, acetylation, flexibility, solubility, interaction with cellulose, stability.
Keywords [sv]
hemicellulosa, trä, glukomannan, xylan, struktur, acetylering, flexibilitet, löslighet, interaktion med cellulosa, stabilitet.
National Category
Wood Science Chemical Sciences Paper, Pulp and Fiber Technology Plant Biotechnology
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-240982ISBN: 978-91-7873-068-1 (print)OAI: oai:DiVA.org:kth-240982DiVA, id: diva2:1275732
Public defence
2019-02-01, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20190107

Available from: 2019-01-07 Created: 2019-01-07 Last updated: 2019-01-07Bibliographically approved
List of papers
1. A molecular dynamics study of the effect of glycosidic linkage type in the hemicellulose backbone on the molecular chain flexibility
Open this publication in new window or tab >>A molecular dynamics study of the effect of glycosidic linkage type in the hemicellulose backbone on the molecular chain flexibility
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2016 (English)In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313XArticle in journal (Refereed) Published
Abstract [en]

The macromolecular conformation of the constituent polysaccharides in lignocellulosic biomass influences their supramolecular interactions, and therefore their function in plants and their performance in technical products. The flexibility of glycosidic linkages from the backbone of hemicelluloses was studied by evaluating the conformational freedom of the φ and ψ dihedral angles using molecular dynamic simulations, additionally selected molecules were correlated with experimental data by nuclear magnetic resonance spectroscopy. Three types of β-(1→4) glycosidic linkages involving the monosaccharides (Glcp, Xylp and Manp) present in the backbone of hemicelluloses were defined. Different di- and tetrasaccharides with combinations of such sugar monomers from hemicelluloses were simulated, and free energy maps of the φ – ψ space and hydrogen-bonding patterns were obtained. The glycosidic linkage between Glc-Glc or Glc-Man (C-type) was the stiffest with mainly one probable conformation; the linkage from Man-Man or Man-Glc (M-type) was similar but with an increased probability for an alternative conformation making it more flexible, and the linkage between two Xyl-units (X-type) was the most flexible with two almost equally populated conformations. Glycosidic linkages of the same type showed essentially the same conformational space in both disaccharides and in the central region of tetrasaccharides. Different probabilities of glycosidic linkage conformations in the backbone of hemicelluloses can be directly estimated from the free energy maps, which to a large degree affect the overall macromolecular conformations of these polymers. The information gained contributes to an increased understanding of the function of hemicelluloses both in the cell wall and in technical products.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
glucomannan, xylan, xyloglucan, computer simulation, nuclear magnetic resonance spectroscopy
National Category
Wood Science
Identifiers
urn:nbn:se:kth:diva-192894 (URN)10.1111/tpj.13259 (DOI)000388442100005 ()2-s2.0-84987605339 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Note

QC 20160927

Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2019-01-08Bibliographically approved
2. Regular Motifs in Xylan Modulate Molecular Flexibility and Interactions with Cellulose Surfaces
Open this publication in new window or tab >>Regular Motifs in Xylan Modulate Molecular Flexibility and Interactions with Cellulose Surfaces
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2017 (English)In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 175, no 4, p. 1579-1592Article in journal (Refereed) Published
Abstract [en]

Xylan is tightly associated with cellulose and lignin in secondary plant cell walls, contributing to its rigidity and structural integrity in vascular plants. However, the molecular features and the nanoscale forces that control the interactions among cellulose microfibrils, hemicelluloses, and lignin are still not well understood. Here, we combine comprehensive mass spectrometric glycan sequencing and molecular dynamics simulations to elucidate the substitution pattern in softwood xylans and to investigate the effect of distinct intramolecular motifs on xylan conformation and on the interaction with cellulose surfaces in Norway spruce (Picea abies). We confirm the presence of motifs with evenly spaced glycosyl decorations on the xylan backbone, together with minor motifs with consecutive glucuronation. These domains are differently enriched in xylan fractions extracted by alkali and subcritical water, which indicates their preferential positioning in the secondary plant cell wall ultrastructure. The flexibility of the 3-fold screw conformation of xylan in solution is enhanced by the presence of arabinofuranosyl decorations. Additionally, molecular dynamic simulations suggest that the glycosyl substitutions in xylan are not only sterically tolerated by the cellulose surfaces but that they increase the affinity for cellulose and favor the stabilization of the 2-fold screw conformation. This effect is more significant for the hydrophobic surface compared with the hydrophilic ones, which demonstrates the importance of nonpolar driving forces on the structural integrity of secondary plant cell walls. These novel molecular insights contribute to an improved understanding of the supramolecular architecture of plant secondary cell walls and have fundamental implications for overcoming lignocellulose recalcitrance and for the design of advanced wood-based materials.

Place, publisher, year, edition, pages
American Society of Plant Biologists, 2017
National Category
Plant Biotechnology
Identifiers
urn:nbn:se:kth:diva-220477 (URN)10.1104/pp.17.01184 (DOI)000417083900007 ()2-s2.0-85037747688 (Scopus ID)
Note

QC 20171222

Available from: 2017-12-22 Created: 2017-12-22 Last updated: 2019-01-07Bibliographically approved
3. The influence of acetylation and sugar composition on the (in)solubility of mannans, their interaction with cellulose surfaces and thermal properties.
Open this publication in new window or tab >>The influence of acetylation and sugar composition on the (in)solubility of mannans, their interaction with cellulose surfaces and thermal properties.
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(English)Manuscript (preprint) (Other academic)
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-240496 (URN)
Note

QC 20190108

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-01-08Bibliographically approved
4. Wood Hemicelluloses Exert Distinct Biomechanical Contributions in Bacterial Cellulose Hydrogels
Open this publication in new window or tab >>Wood Hemicelluloses Exert Distinct Biomechanical Contributions in Bacterial Cellulose Hydrogels
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(English)Manuscript (preprint) (Other academic)
National Category
Materials Engineering Biological Sciences Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-240497 (URN)
Note

QC 20190108

Available from: 2018-12-19 Created: 2018-12-19 Last updated: 2019-01-08Bibliographically approved
5. The degree of acetylation affects the microbial degradability of mannans
Open this publication in new window or tab >>The degree of acetylation affects the microbial degradability of mannans
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2016 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 133, p. 36-46Article in journal (Refereed) Published
Abstract [en]

Hemicelluloses as major components of plant cell walls are acetylated to different extents. The biologicalfunctions of acetylation are not completely understood but suggested that one reason is to decrease themicrobial degradability of cell walls. Model seed galactomannan and glucomannan, which are structurallysimilar to an abundant class of wood hemicelluloses, were acetylated to various degrees and usedas sole carbon source on agar plates for microbial growth. When soil samples were inoculated on theplates, significantly fewer strains grew on the agar plates with highly acetylated mannans than withslightly acetylated or non-acetylated mannans. One filamentous fungus isolated and identified as aPenicillium species was shown to grow faster and stronger on non-acetylated than on highly acetylatedmannan. The data therefore support the hypothesis that a high degree of acetylation (DSac) can decreasethe microbial degradability of hemicelluloses. Possible mechanisms and the technological significance ofthis are discussed.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Wood biodegradation, Acetylation, Hemicellulose, Mannan, Microorganism, Biodegradability
National Category
Wood Science
Identifiers
urn:nbn:se:kth:diva-192902 (URN)10.1016/j.polymdegradstab.2016.07.009 (DOI)000386403100005 ()2-s2.0-84989832176 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20160926

Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2019-01-07Bibliographically approved
6. Mannanase hydrolysis of spruce galactoglucomannan focusing on the influence of acetylation on enzymatic mannan degradation
Open this publication in new window or tab >>Mannanase hydrolysis of spruce galactoglucomannan focusing on the influence of acetylation on enzymatic mannan degradation
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2018 (English)In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 11, article id 114Article in journal (Refereed) Published
Abstract [en]

Background: Galactoglucomannan (GGM) is the most abundant hemicellulose in softwood, and consists of a backbone of mannose and glucose units, decorated with galactose and acetyl moieties. GGM can be hydrolyzed into fermentable sugars, or used as a polymer in films, gels, and food additives. Endo-beta-mannanases, which can be found in the glycoside hydrolase families 5 and 26, specifically cleave the mannan backbone of GGM into shorter oligosaccharides. Information on the activity and specificity of different mannanases on complex and acetylated substrates is still lacking. The aim of this work was to evaluate and compare the modes of action of two mannanases from Cellvibrio japonicus (CjMan5A and CjMan26A) on a variety of mannan substrates, naturally and chemically acetylated to varying degrees, including naturally acetylated spruce GGM. Both enzymes were evaluated in terms of cleavage patterns and their ability to accommodate acetyl substitutions. Results: CjMan5A and CjMan26A demonstrated different substrate preferences on mannan substrates with distinct backbone and decoration structures. CjMan5A action resulted in higher amounts of mannotriose and mannotetraose than that of CjMan26A, which mainly generated mannose and mannobiose as end products. Mass spectrometric analysis of products from the enzymatic hydrolysis of spruce GGM revealed that an acetylated hexotriose was the shortest acetylated oligosaccharide produced by CjMan5A, whereas CjMan26A generated acetylated hexobiose as well as diacetylated oligosaccharides. A low degree of native acetylation did not significantly inhibit the enzymatic action. However, a high degree of chemical acetylation resulted in decreased hydrolyzability of mannan substrates, where reduced substrate solubility seemed to reduce enzyme activity. Conclusions: Our findings demonstrate that the two mannanases from C. japonicus have different cleavage patterns on linear and decorated mannan polysaccharides, including the abundant and industrially important resource spruce GGM. CjMan26A released higher amounts of fermentable sugars suitable for biofuel production, while CjMan5A, producing higher amounts of oligosaccharides, could be a good candidate for the production of oligomeric platform chemicals and food additives. Furthermore, chemical acetylation of mannan polymers was found to be a potential strategy for limiting the biodegradation of mannan-containing materials.

Place, publisher, year, edition, pages
BIOMED CENTRAL LTD, 2018
Keywords
Lignocellulose, Spruce, Galactoglucomannan, Endo-beta-mannanases, GH5, GH26, Cellvibrio japonicus, Polysaccharide acetylation, Enzymatic degradation pattern, Acetyl esterases
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-227774 (URN)10.1186/s13068-018-1115-y (DOI)000430977200001 ()29713374 (PubMedID)2-s2.0-85045688074 (Scopus ID)
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 621-2014-5295
Note

QC 20180514

Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2019-01-07Bibliographically approved
7. The structure of galactoglucomannan impacts the degradation under alkaline conditions
Open this publication in new window or tab >>The structure of galactoglucomannan impacts the degradation under alkaline conditions
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2018 (English)In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882XArticle in journal (Refereed) Published
Abstract [en]

Galactoglucomannan (GGM) from sprucewas studied with respect to the degradation behavior inalkaline solution. Three reference systems includinggalactomannan from locust bean gum, glucomannanfrom konjac and the linear water-soluble carboxymethylcellulose were studied with focus onmolecular weight, sugar composition, degradationproducts, as well as formed oligomers, to identifyrelative structural changes in GGM. Initially allmannan polysaccharides showed a fast decrease inthe molecular weight, which became stable in the laterstage. The degradation of the mannan polysaccharidescould be described by a function corresponding to thesum of two first order reactions; one slow that wasascribed to peeling, and one fast that was connectedwith hydrolysis. The galactose side group wasstable under conditions used in this study (150 min,90 C, 0.5 M NaOH). This could suggest that, apartfrom the covalent connection to C6 in mannose, thegalactose substitutions also interact non-covalentlywith the backbone to stabilize the structure againstdegradation. Additionally, the combination of differentbackbone sugars seems to affect the stability of thepolysaccharides. For carboxymethyl cellulose thedegradation was linear over time which furthersuggests that the structure and sugar composition playan important role for the alkaline degradation. Moleculardynamics simulations gave details about theconformational behavior of GGM oligomers in watersolution, as well as interaction between the oligomersand hydroxide ions.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
Hemicellulose, Spruce, Alkaline hydrolysis, Peeling, Structural analysis, Molecular dynamics simulations
National Category
Polymer Technologies Wood Science
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-225161 (URN)10.1007/s10570-018-1737-z (DOI)2-s2.0-85043365333 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20180405

Available from: 2018-04-03 Created: 2018-04-03 Last updated: 2019-01-08Bibliographically approved

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The full text will be freely available from 2019-12-31 20:00
Available from 2019-12-31 20:00

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7891011121310 of 17
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