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Chemical and structural factors influencing enzymatic saccharification of wood from aspen, birch and spruce
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2018 (English)In: Biomass and Bioenergy, ISSN 0961-9534, E-ISSN 1873-2909, Vol. 109, p. 125-134Article in journal (Refereed) Published
Abstract [en]

The susceptibility of untreated and sulfuric-acid-pretreated aspen, birch, and spruce to analytical enzymatic saccharification was studied in relation to their chemical composition and physical-structural features. The analytical data collected covered the mass fractions of lignin, carbohydrates, and extractives, the release of acetic acid, formic acid, and uronic acids by acid and alkaline hydrolysis, crystallinity and crystallite size, syringyl: guaiacyl (S:G) ratio of lignin, cellulose accessibility, FTIR spectra, images from SEM and fluorescence microscopy, and susceptibility to enzymatic saccharification using enzyme mixtures with and without supplementary xylanase.In the absence of pretreatment the mass fraction yield of Glc on the original dry wood in the analytical enzymatic saccharification increased in the order birch (16 g kg−1) < spruce (35 g kg−1) < aspen (150 g kg−1). After acid pretreatment, the order changed to spruce (170 g kg−1) < aspen (290 g kg−1), birch (290 g kg−1). The relatively high recalcitrance of untreated birch was not possible to relate to mass fraction of lignin, S:G ratio, cellulose crystallinity, or mass fraction of acetyl, but rather to structural features, such as a more compact surface structure with high density and low cellulose accessibility. The relatively high sugar yields from both untreated and pretreated aspen suggest that aspen wood is well suited as feedstock for production of liquid biofuels and green chemicals in forest-based biorefineries.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 109, p. 125-134
Keywords [en]
Hardwood, Softwood, Chemical composition, Dilute-acid pretreatment, Enzymatic saccharification, Physical structure
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:umu:diva-143889DOI: 10.1016/j.biombioe.2017.12.020ISI: 000424939200015OAI: oai:DiVA.org:umu-143889DiVA, id: diva2:1173562
Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-08-06Bibliographically approved
In thesis
1. Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability
Open this publication in new window or tab >>Recalcitrance of wood to biochemical conversion: feedstock properties, pretreatment, saccharification, and fermentability
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lignocellulose is an inexpensive and abundant renewable resource that can be used to produce advanced biofuels, green chemicals, and other bio-based products. Pretreatment and efficient enzymatic saccharification are essential features of bioconversion of lignocellulosic biomass. The aims of the research were to achieve a better understanding of the recalcitrance of woody biomass to bioconversion, to explore different pretreatment techniques that can be used to decrease the recalcitrance of the biomass and improve the digestibility of the cellulose, and to investigate by-products of acid pretreatment that cause enzymes and microorganisms to work less efficiently.

The recalcitrance of wood from aspen, birch, and spruce was investigated before and after acid pretreatment. Before pretreatment, birch exhibited the highest recalcitrance, which was attributed to structural factors. After pretreatment, spruce showed the highest recalcitrance, which was attributed to chemical factors, such as high lignin content. Deacetylation of hybrid aspen in planta by a CE5 acetyl xylan esterase decreased the recalcitrance, and the glucose yield of enzymatic saccharification of non-pretreated wood increased with 27%.

Pretreatment options based on ionic liquids and steam explosion were further explored. The effects of the anionic constituents of a series of imidazolium-based ionic liquids on pretreatment of aspen and spruce were investigated. [HSO4]− was efficient only for aspen, which was attributed to acid degradation of xylan. [MeCO2]− was efficient for both aspen and spruce, which was attributed to its capability to create a disordered cell wall structure rather than to removal of lignin and hemicellulose. A comparison was made between using sulfuric acid and sulfur dioxide for pretreatment of spruce. Although sulfur dioxide resulted in a pretreatment liquid that was more inhibitory to both enzymes and yeast, it was still superior to pretreatment with sulfuric acid, a phenomenon that was attributed to the particle size of the pretreated material.

In a comparison of microbial inhibitors in pretreatment liquids from steam explosion of spruce, formaldehyde was found to be the most important inhibitor of yeast. Enzyme inhibition by catalytically non-productive adsorption to lignins and pseudo-lignin was investigated using quantitative proteomics. The results indicate that protein adsorption to pseudo-lignin can be as extensive as adsorption to real lignin. 

Place, publisher, year, edition, pages
Umeå: Umeå University, 2018. p. 59
Keywords
Recalcitrance, Pretreatment, Enzymatic saccharification, Ionic liquid, Steam explosion, Enzyme inhibition, Non-productive binding, Microbial inhibitors
National Category
Bioprocess Technology Wood Science Biochemicals
Identifiers
urn:nbn:se:umu:diva-145045 (URN)978-91-7601-853-8 (ISBN)
Public defence
2018-03-16, KBC-huset, Lilla Hörsalen, KB.E3.01, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2018-02-23 Created: 2018-02-19 Last updated: 2018-06-09Bibliographically approved

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