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The degree of acetylation affects the microbial degradability of mannans
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0001-8135-588X
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0003-0277-2269
KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0003-3572-7798
KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0002-3372-8773
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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. Vol. 133, p. 36-46
Keywords [en]
Wood biodegradation, Acetylation, Hemicellulose, Mannan, Microorganism, Biodegradability
National Category
Wood Science
Identifiers
URN: urn:nbn:se:kth:diva-192902DOI: 10.1016/j.polymdegradstab.2016.07.009ISI: 000386403100005Scopus ID: 2-s2.0-84989832176OAI: oai:DiVA.org:kth-192902DiVA, id: diva2:972826
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20160926

Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2019-01-07Bibliographically approved
In thesis
1. Wood Hemicelluloses - Fundamental Insights on Biological and Technical Properties
Open this publication in new window or tab >>Wood Hemicelluloses - Fundamental Insights on Biological and Technical Properties
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
hemicellulose, wood, glucomannan, xylan, structure, acetylation, flexibility, solubility, interaction with cellulose, stability., 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:nbn:se:kth:diva-240982 (URN)978-91-7873-068-1 (ISBN)
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

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