| 1. |
- Faryar, Reza
(författare)
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Conversion of xylan into value-added products
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today’s high demand on finding sustainable energy sources, replacing petroleum-based products and the needfor healthier food alternatives have forced us to search for natural recoverable resources and explore their manyhidden applications. One such resource is xylan, which has gained much attention as possible raw material forvarious exploitations. However, its wider industrial application puts demand on research achievements to reacha marketable product. The work throughout this thesis was focused on studying some of these applications withthe aim to improve the final product or its production process.Production of alkyl xylobioside and alkyl xylotrioside was achieved using a highly thermostable recombinantendoxylanase from Thermotoga neapolitana. This enzyme made it possible to directly react xylan with an alcoholto produce surfactant without the need for its hydrolysis to xylooligosaccharides (XOS). Furthermore, the effectof xylan concentration, enzyme dose, reaction water content, reaction temperature and initial pH on the yield ofthese surfactants was studied (Paper I).XOS as prebiotic, another remarkable product from xylan, was produced from wheat straw. Xylan was firstextracted with alkali and later hydrolysed to XOS using a variant of an alkali-tolerant endoxylanase from Bacillushalodurans S7. Its prebiotic properties were confirmed by growth of a putative probiotic strain; Lactobacillusbrevis DSM 1269 (Paper II). To further study this strain and understand how it utilizes the XOS we studied oneof its enzymes, a β-xylosidase from glycoside hydrolase family 43 (GH43). The kinetic studies using XOS ofdifferent chain length revealed that the enzyme displayed a higher catalytic efficiency for shorter chain lengthsubstrate, in line with data showing that XOS of short chain length can be taken up by L. brevis. Moreover, themolecular structure of this enzyme was solved using X ray crystallography showing a tetrameric structure, whichfurther assisted to better understand its catalytic activity in relation to its structure (Paper III).The potential application of xylan as film and coating was the driving force for our final study. For this purpose,arabinoxylan was mixed with tragacanth as a second polymer and cross-linked with malic acid. Based on theinitial type of arabinoxylan used, two types of films were produced with similar tensile strength and thermaldecomposition curves but significantly different elongation at break and swelling ratios. With further studies thesefilms have the potential to be used as edible films, wound dressing or drug coating (Paper IV).
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| 2. |
- Faryar, Reza, et al.
(författare)
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Production of prebiotic xylooligosaccharides from alkaline extracted wheat straw using the K80R-variant of a thermostable alkali-tolerant xylanase
- 2015
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Ingår i: Food and Bioproducts Processing. - : Elsevier BV. - 1744-3571 .- 0960-3085. ; 93:Online 22 November 2014, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural by-products are raw materials of importance for increased utilization of renewable biomass. Wheat straw is a raw material of significant production volume and is in this work used for production of xylooligosaccharides (XOS). Extraction of xylan by dilute alkali was followed by hydrolysis using a variant of the alkali-tolerant Bacillus halodurans S7 endoxylanase A mutated at K80R. The xylan yield was on average 56.5 g xylose equivalents per kg dried, ground wheat straw, with 1 arabinose per 12 xylose residues. The K80R variant, which displayed higher specific activity than the wild-type enzyme, was added at a load of 96 U/g extracted xylan. The XOS-yield (xylobiose – xylopentaose) was evaluated at time intervals in the temperature range of 50 to 65 degrees C, at pHs from 7 to 10. The enzyme was optimally active at 60 degrees C up to pH 9. Hydrolysis was completed within 7 h, resulting in 36 % conversion of the xylan to predominantly xylobiose. Xylose content was low (2.4%) despite extended incubation, which is desirable for XOS-production. The XOS-containing hydrolysate was confirmed as a suitable carbon source for the putative probiotic strain Lactobacillus brevis DSM 1269, showing the applicability of the method to obtain prebiotic XOS.
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| 3. |
- Mamo, Gashaw, et al.
(författare)
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Microbial glycoside hydrolases for biomass utilization in biofuels application
- 2013
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Ingår i: Biofuel Technologies: Recent Developments. - 9783642345180 ; , s. 171-188
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Bokkapitel (refereegranskat)abstract
- Renewable biomass is predicted to have the potential to meet at least a quarter of the world demand for transportation fuel, but to do so both terrestrial lignocellulosic as well as marine algal resources need to be efficiently utilized. In the processes where these biomasses are converted to different types of energy-carriers (for example fuel alcohols e.g. ethanol or butanol) microbial glycoside hydrolases have a role in the saccharification process. During saccharification polymeric carbohydrate resources (e.g. starch, cellulose or hemicellulose) are hydrolysed into mono and oligosaccharides that can be utilized by the organism selected to ferment these carbohydrates into the desired energy-carrier. This chapter aims to shed light on different processing alternatives for the conversion of lignocellulose or algal starch into mono or oligosaccharides, and what roles the microbial glycoside hydrolases have as processing aids in these conversions.
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| 4. |
- Mamo, Gashaw, et al.
(författare)
-
Microbial glycoside hydrolases for biomass utilization in biofuels applications
- 2014
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Ingår i: Biofuel Technologies : Recent Developments - Recent Developments. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 3642345182 - 9783642345180 - 9783642345197 ; , s. 171-188
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Bokkapitel (refereegranskat)abstract
- Renewable biomass is predicted to have the potential to meet at least a quarter of the world demand for transportation fuel, but to do so both terrestrial lignocellulosic as well as marine algal resources need to be efficiently utilized. In the processes where these biomasses are converted into different types of energy carriers (for example fuel-alcohols e.g. ethanol or butanol) microbial glycoside hydrolases (GHs) have a role in the saccharification process. During saccharification polymeric carbohydrate resources (e.g. starch, cellulose or hemicellulose) are hydrolyzed into mono and oligosaccharides that can be utilized by the organism selected to ferment these carbohydrates into the desired energy-carrier. This chapter aims to shed light on different processing alternatives for the conversion of lignocellulose or algal starch into mono or oligosaccharides, and what roles the microbial GHs have as processing aids in these conversions.
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| 5. |
- Mamo, Gashaw, et al.
(författare)
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Surfactants from xylan: Production of n-octyl xylosides using a highly thermostable xylanase from Thermotoga neapolitana
- 2010
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Ingår i: Process Biochemistry. - : Elsevier BV. - 1873-3298 .- 1359-5113. ; 45:5, s. 700-705
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Tidskriftsartikel (refereegranskat)abstract
- A highly thermostable recombinant xylanase from Thermotoga neapolitana was used as a catalyst for single-step synthesis of n-octyl xylobioside and n-octyl xylotrioside from xylan and n-octanol. Effect of xylan concentration, enzyme dose, reaction water content, reaction temperature and initial pH on the yield of these surfactants has been studied. The optimal conditions for n-octyl xylobioside and n-octyl xylotrioside synthesis are found to be different. The maximum n-octyl xylobioside and n-octyl xylotrioside yield were 120 and 38 mg/g of xylan, respectively. The n-octyl xylobioside yield achieved in this study was better than the yield achieved in all other enzymatic synthesis studies reported so far except what is achieved with the use of supercritical fluoroform under high pressure. The n-octyl xylotrioside yield is the highest ever achieved through enzymatic synthesis. An integrated system of production and recovery of n-octyl xylosides has improved the yield of n-octyl xylobioside and n-octyl xylotrioside by a factor of 1.7 and 2.4, respectively. (C) 2010 Elsevier Ltd. All rights reserved.
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