| 1. |
- Gullfot, Fredrika, 1967-
(författare)
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Synthesis of xyloglucan oligo- and polysaccharides with glycosynthase technology
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Xyloglucans are polysaccharides found as storage polymers in seeds and tubers, and as cross-linking glycans in the cell wall of plants. Their structure is complex with intricate branching patterns, which contribute to the physical properties of the polysaccharide including its binding to and interaction with other glycans such as cellulose. Xyloglucan is widely used in bulk quantities in the food, textile and paper making industries. With an increasing interest in technically more advanced applications of xyloglucan, such as novel biocomposites, there is a need to understand and control the properties and interactions of xyloglucan with other compounds, to decipher the relationship between xyloglucan structure and function, and in particular the effect of different branching patterns. However, due to the structural heterogeneity of the polysaccharide as obtained from natural sources, relevant studies have not been possible to perform in practise. This fact has stimulated an interest in synthetic methods to obtain xyloglucan mimics and analogs with well-defined structure and decoration patterns. Glycosynthases are hydrolytically inactive mutant glycosidases that catalyse the formation of glycosidic linkages between glycosyl fluoride donors and glycoside acceptors. Since its first conception in 1998, the technology is emerging as a useful tool in the synthesis of large, complex polysaccharides. This thesis presents the generation and characterisation of glycosynthases based on xyloglucanase scaffolds for the synthesis of well-defined homogenous xyloglucan oligo- and polysaccharides with regular substitution patterns.
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| 2. |
- Sunner, Hampus, 1981, et al.
(författare)
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Fungal Ferulic Acid Esterases – Specificity and Phylogeny
- 2009
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Ingår i: Italic5 Science and Technology of Biomasses Proceedings Book, M Orlandi, C Crestine (Ed.). Italic5/COST conference, Sept 1-4 2009, Varenna, Italy.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ferulic Acid Esterases (FAE) is a large heterogeneous group of enzymes with activity on esters of hydroxy- and metoxy- substituted cinnamic acid derivatives, such as ferulic acid. These ester bonds occur in the cell walls of plants and are especially common in grasses. As little systematic knowledge has been collected about this group of enzymes and only a few enzymes have been biochemically characterised to date, we have explored the phylogeny of FAEs using bioinformatic tools. We can conclude that the known Ferulic Acid Esterases belong to several evolutionary distant groups, two of which have dozens of highly related sequences, and a few groups with no members other than the known enzyme. The phylogeny also suggests certain similarities of substrate specificity within groups and proposes enzymes, whose biochemical characterisation would be especially informative for our understanding of the FAE families.
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| 3. |
- Abedinifar, S., et al.
(författare)
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Ethanol production by Mucor indicus and Rhizopus oryzae from rice straw by separate hydrolysis and fermentation
- 2009
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 0961-9534 .- 1873-2909. ; 33:5, s. 828-833
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Tidskriftsartikel (refereegranskat)abstract
- Rice straw was successfully converted to ethanol by separate enzymatic hydrolysis and fermentation by Mucor indicus, Rhizopus oryzae, and Saccharomyces cerevisiae. The hydrolysis temperature and pH of commercial cellulase and β-glucosidase enzymes were first investigated and their best performance obtained at 45 °C and pH 5.0. The pretreatment of the straw with dilute-acid hydrolysis resulted in 0.72 g g-1 sugar yield during 48 h enzymatic hydrolysis, which was higher than steam-pretreated (0.60 g g-1) and untreated straw (0.46 g g-1). Furthermore, increasing the concentration of the dilute-acid pretreated straw from 20 to 50 and 100 g L-1 resulted in 13% and 16% lower sugar yield, respectively. Anaerobic cultivation of the hydrolyzates with M. indicus resulted in 0.36-0.43 g g-1 ethanol, 0.11-0.17 g g-1 biomass, and 0.04-0.06 g g-1 glycerol, which is comparable with the corresponding yields by S. cerevisiae (0.37-0.45 g g-1 ethanol, 0.04-0.10 g g-1 biomass and 0.05-0.07 glycerol). These two fungi produced no other major metabolite from the straw and completed the cultivation in less than 25 h. However, R. oryzae produced lactic acid as the major by-product with yield of 0.05-0.09 g g-1. This fungus had ethanol, biomass and glycerol yields of 0.33-0.41, 0.06-0.12, and 0.03-0.04 g g-1, respectively.
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| 4. |
- Enoksson, Peter, 1957, et al.
(författare)
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Micro- and Nanosystems for Sensing in Medicine
- 2008
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Ingår i: Proceedings of Medicinteknikdagarna 2008, 14-15 October, Göteborg, Sweden. ; , s. 117-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Hjortmo, Sofia, 1978
(författare)
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On Folates in Yeasts -Exploring Yeasts as Vehicles for Biofortification of Folates in Food
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High intake of the B vitamin folate during pregnancy is known to decrease the risk for development of neural tube defects. In addition, a good folate status may prevent the progression of several diseases such as megaloblastic anaemia, cardiovascular disease, cancer and Alzheimer’s disease. However, reaching sufficient amounts via the diet only is complicated and new strategies must be developed to increase the mean folate intake. The aim of this thesis is to explore the use of yeasts for biofortification of folates in food. Yeasts synthesise folates de novo and may constitute potent vehicles for natural folates. Current work includes investigations of folate content and composition in yeasts as well as studies of the impact of growth rate and chemical environments on folate levels in Saccharomyces cerevisiae (Baker’s yeast). The applicability of the results was then investigated in two food model systems (bread and a cereal-based fermented porridge called togwa) to demonstrate the practical relevance. In a screening of 52 yeast strains, the folate content ranged from 40 to 145 µg per gram dry matter of yeast, showing that inherent variations in yeast folate levels exist. Several S. cerevisiae strains showed at least a two-fold higher folate content than a commercial Baker’s strain, indicating possibilities to increase folates in fermented foods simply by choosing the proper strain. With regard to cultivation conditions, folates in S. cerevisiae were demonstrated to increase linearly with growth rate in a defined medium, showing that high growth rate, i.e. respiro-fermentative metabolism, is most favourable for high folate content. Cultivation in a rich medium yielded cells containing lower amounts of folate compared to cells grown in a poor chemical environment even though the specific growth rate was higher in the rich medium. The results obtained show that the growth rate per se could not predict intracellular folate concentrations and that the chemical environment has a substantial impact on intracellular folates. By applying strain selection and cultivation at optimal conditions prior to baking we were able to increase folates five-fold in white wheat bread compared to bread leavened with commercial Baker’s yeast. In addition, folates increased at most 23-fold during yeast fermentations in a cereal-based porridge (togwa) compared to togwa raw material. Final folate levels were shown to be highly dependent on strain and cultivation time. The results demonstrate that yeasts constitute flexible and controllable vehicles for biofortification of folates in fermented food.
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| 6. |
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| 7. |
- Lennartsson, Patrik R, 1983, et al.
(författare)
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Effects of different growth forms of Mucor indicus on cultivation on dilute-acid lignocellulosic hydrolyzate, inhibitor tolerance, and cell wall composition
- 2009
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Ingår i: Journal of Biotechnology. - : Elsevier BV. - 0168-1656 .- 1873-4863. ; 143:4, s. 255-261
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Tidskriftsartikel (refereegranskat)abstract
- The dimorphic fungus Mucor indicus was grown in different forms classified as purely filamentous, mostly filamentous, mostly yeast-like and purely yeast-like, and the relationship between morphology and metabolite production, inhibitor tolerance and the cell wall composition was investigated. Low concentrations of spores in the inoculum with subsequent aeration promoted filamentous growth, whereas higher spore concentrations and anaerobic conditions promoted yeast-like growth. Ethanol was the main metabolite with glycerol next under all conditions tested. The yields of ethanol from glucose were between 0.39 and 0.42 g g(-1) with productivities of 3.2-5.0 g l(-1) h(-1). The ethanol productivity of mostly filamentous cells was increased from 3.9 to 5.0 g l(-1) h(-1) by the presence of oxygen, whereas aeration of purely yeast-like cells showed no such effect. All growth forms were able to tolerate 4.6 g l(-1) furfural and 10 g l(-1) acetic acid and assimilate the sugars, although with different consumption rates. The cell wall content of the fungus measured as alkali insoluble materials (AIM) of the purely yeast-like cells was 26% of the biomass, compared to 8% of the pure filaments. However, the chitosan concentration of the filaments was 29% of the AIM, compared to 6% of the yeast-like cells.
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| 8. |
- Millati, Ria, 1972, et al.
(författare)
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Ethanol production from xylose and wood hydrolyzate by Mucor indicus at different aeration rates
- 2008
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126 .- 1930-2126. ; 3:4, s. 1020-1029
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Tidskriftsartikel (refereegranskat)abstract
- The fungus Mucor indicus is able to produce ethanol from xylose as well as dilute-acid lignocellulosic hydrolyzates. The fungus completely assimilated 10 g/L xylose as the sole carbon and energy source within 32 to 65 h at an aeration rate of 0.1 to 1.0 vvm. The highest ethanol yield was 0.16 g/g at 0.1 vvm. Xylitol was formed intermediately with a maximum yield of 0.22 g/g at 0.5 vvm., but disappeared towards the end of experiments. During cultivation in a mixture of xylose and glucose, the fungus did not assimilate xylose as long as glucose was present in the medium. The anaerobic cultivation of the fungus in the hydrolyzate containing 20% xylose and 80% hexoses resulted in no assimilation of xylose but complete consumption of the hexoses in less than 15 h. The ethanol yield was 0.44 g/g. However, the xylose in the hydrolyzate was consumed when the media were aerated at 0.067 to 0.333 vvm. The best ethanol yield was 0.44 g/g at 0.067 vvm. The results of this study suggest that M. indicus hydrolyzate can be first fermented anaerobically for hexose assimilation and subsequently continued under oxygen-limited conditions for xylose fermentation.
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| 9. |
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| 10. |
- Taherzadeh, M.J., et al.
(författare)
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Enzymatic-based hydrolysis processes for ethanol from lignocellulosic materials : A review.
- 2007
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126 .- 1930-2126. ; 2:4, s. 707-738
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Tidskriftsartikel (refereegranskat)abstract
- This article reviews developments in the technology for ethanol production from lignocellulosic materials by “enzymatic” processes. Several methods of pretreatment of lignocelluloses are discussed, where the crystalline structure of lignocelluloses is opened up, making them more accessible to the cellulase enzymes. The characteristics of these enzymes and important factors in enzymatic hydrolysis of the cellulose and hemicellulose to cellobiose, glucose, and other sugars are discussed. Different strategies are then described for enzymatic hydrolysis and fermentation, including separate enzymatic hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), non-isothermal simultaneous saccharification and fermentation (NSSF), simultaneous saccharification and co-fermentation (SSCF), and consolidated bioprocessing (CBP). Furthermore, the by-products in ethanol from lignocellulosic materials, wastewater treatment, commercial status, and energy production and integration are reviewed.
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