| 1. |
- Anasontzis, George E, 1980
(författare)
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Biomass modifying enzymes: From discovery to application
- 2012
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Ingår i: Oral presentation at the Chalmers Life Science AoA conference.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has now been realized that the road towards the bio-based economy is a one-way street, leaving gradually the oil-based technology and driving slowly towards a more sustainable society. The current non-biodegradable hydrocarbon fuels and plastics will be replaced by new products which will derive from natural and renewable resources. The synthesis of such biofuels and biochemicals is still challenged by the difficulties to cost efficiently degrade lignocellulosic material to fermentable sugars or to isolate the intact polymers. Biomass degrading and modifying enzymes play an integral role both in the separation of the polymers from the wood network, as well as in their subsequent modification, prior to further product development.Our group interests focus on all levels of applied enzyme research of biomass acting enzymes: Discovery, assay development, production and application. Relevant examples will be provided: What is our strategy for discovering novel microorganisms and enzymes from the tropical forests and grasslands of Vietnam? How do we design novel real-world assays for enzyme activity determination? Which are the bottlenecks in the enzymatic cellulose hydrolysis? How enzymes can be used to produce high added value compounds from biomass?
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| 2. |
- Ask, Magnus, 1983
(författare)
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Towards More Robust Saccharomyces cerevisiae Strains for Lignocellulosic Bioethanol Production: Lessons from process concepts and physiological investigations
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dwindling oil reserves and the negative impacts of fossil fuels on the environment call for more sustainable energy sources. First-generation bioethanol produced from sugar cane and corn has met some of these needs, but it competes with the food supply for raw materials. Lignocellulosic biomass is an abundant non-edible raw material that can be converted to ethanol using the yeast Saccharomyces cerevisiae. However, due to the inherent recalcitrance to degradation of lignocellulosic raw materials, harsh pretreatment methods must be used to liberate fermentable sugars, resulting in the release of compounds such as acetic acid, furan aldehydes and phenolics, that inhibit yeast metabolism. This thesis research aimed to identify bottlenecks in terms of inhibitory compounds related to ethanol production from two lignocellulosic raw materials, Arundo donax and spruce, and furthermore to harness the physiological responses to these inhibitors to engineer more robust yeast strains. A comparative study of separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) revealed that acetic acid limits xylose utilization in pretreated Arundo donax, whereas the furan aldehydes furfural and 5-hydroxymethyl-2-furaldehyde (HMF) were hypothesized to be key inhibitors in pretreated spruce. The impacts of furfural and HMF on the redox and energy metabolism of S. cerevisiae were studied in detail in chemostat and batch cultivations. After adding the inhibitors to the feed medium of chemostat cultivations, the intracellular levels of NADH, NADPH, and ATP were found to decrease by 40, 75, and 19%, respectively, suggesting that furan aldehydes drain the cells of reducing power. A strong effect on redox metabolism was also observed after pulsing furfural and HMF in the xylose consumption phase in batch cultures. The drainage of reducing power was also observed in a genome-wide study of transcription that found that genes related to NADPH-requiring processes, such as nitrogen and sulphur assimilation, were significantly induced. The redox metabolism was engineered by overproducing the protective metabolite and antioxidant glutathione. Strains with an increased intracellular level of reduced glutathione were found to sustain ethanol production for longer duration in SSF of pretreated spruce, yielding 70% more ethanol than did the wild type strain.
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| 3. |
- Ylitervo, Päivi
(författare)
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Concepts for improving ethanol productivity from lignocellulosic materials : encapsulated yeast and membrane bioreactors
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignocellulosic biomass is a potential feedstock for production of sugars, which can be fermented into ethanol. The work presented in this thesis proposes some solutions to overcome problems with suboptimal process performance due to elevated cultivation temperatures and inhibitors present during ethanol production from lignocellulosic materials. In particular, continuous processes operated at high dilution rates with high sugar utilisation are attractive for ethanol fermentation, as this can result in higher ethanol productivity. Both encapsulation and membrane bioreactors were studied and developed to achieve rapid fermentation at high yeast cell density. My studies showed that encapsulated yeast is more thermotolerant than suspended yeast. The encapsulated yeast could successfully ferment all glucose during five consecutive batches, 12 h each at 42 °C. In contrast, freely suspended yeast was inactivated already in the second or third batch. One problem with encapsulation is, however, the mechanical robustness of the capsule membrane. If the capsules are exposed to e.g. high shear forces, the capsule membrane may break. Therefore, a method was developed to produce more robust capsules by treating alginate-chitosan-alginate (ACA) capsules with 3-aminopropyltriethoxysilane (APTES) to get polysiloxane-ACA capsules. Of the ACA-capsules treated with 1.5% APTES, only 0–2% of the capsules broke, while 25% of the untreated capsules ruptured within 6 h in a shear test. In this thesis membrane bioreactors (MBR), using either a cross-flow or a submerged membrane, could successfully be applied to retain the yeast inside the reactor. The cross-flow membrane was operated at a dilution rate of 0.5 h-1 whereas the submerged membrane was tested at several dilution rates, from 0.2 up to 0.8 h-1. Cultivations at high cell densities demonstrated an efficient in situ detoxification of very high furfural levels of up to 17 g L-1 in the feed medium when using a MBR. The maximum yeast density achieved in the MBR was more than 200 g L-1. Additionally, ethanol fermentation of nondetoxified spruce hydrolysate was possible at a high feeding rate of 0.8 h-1 by applying a submerged membrane bioreactor, resulting in ethanol productivities of up to 8 g L-1 h-1. In conclusion, this study suggests methods for rapid continuous ethanol production even at stressful elevated cultivation temperatures or inhibitory conditions by using encapsulation or membrane bioreactors and high cell density cultivations.
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| 4. |
- Ylitervo, Päivi, et al.
(författare)
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Continuous Ethanol Production with a Membrane Bioreactor at High Acetic Acid Concentrations
- 2014
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Ingår i: Membranes. - : MDPI. - 2077-0375. ; 4:3, s. 372-387
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Tidskriftsartikel (refereegranskat)abstract
- The release of inhibitory concentrations of acetic acid from lignocellulosic raw materials during hydrolysis is one of the main concerns for 2nd generation ethanol production. The undissociated form of acetic acid can enter the cell by diffusion through the plasma membrane and trigger several toxic effects, such as uncoupling and lowered intracellular pH. The effect of acetic acid on the ethanol production was investigated in continuous cultivations by adding medium containing 2.5 to 20.0 g•L−1 acetic acid at pH 5.0, at a dilution rate of 0.5 h−1. The cultivations were performed at both high (~25 g•L−1) and very high (100–200 g•L−1) yeast concentration by retaining the yeast cells inside the reactor by a cross-flow membrane in a membrane bioreactor. The yeast was able to steadily produce ethanol from 25 g•L−1 sucrose, at volumetric rates of 5–6 g•L−1•h−1 at acetic acid concentrations up to 15.0 g•L−1. However, the yeast continued to produce ethanol also at a concentration of 20 g•L−1 acetic acid but at a declining rate. The study thereby demonstrates the great potential of the membrane bioreactor for improving the robustness of the ethanol production based on lignocellulosic raw materials.
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| 5. |
- Olofsson, Martin, 1975-, et al.
(författare)
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Combined Effects of Nitrogen Concentration and Seasonal Changes on the Production of Lipids in Nannochloropsis oculata
- 2014
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Ingår i: Marine Drugs. - Basel, Switzerland : MDPI AG. - 1660-3397. ; 12:4, s. 1891-1910
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Tidskriftsartikel (refereegranskat)abstract
- Instead of sole nutrient starvation to boost algal lipid production, we addressed nutrient limitation at two different seasons (autumn and spring) during outdoor cultivation in flat panel photobioreactors. Lipid accumulation, biomass and lipid productivity and changes in fatty acid composition of Nannochloropsis oculata were investigated under nitrogen (N) limitation (nitrate:phosphate N:P 5, N:P 2.5 molar ratio). N. oculata was able to maintain a high biomass productivity under N-limitation compared to N-sufficiency (N:P 20) at both seasons, which in spring resulted in nearly double lipid productivity under N-limited conditions (0.21 g L−1 day−1) compared to N-sufficiency (0.11 g L−1 day−1). Saturated and monounsaturated fatty acids increased from 76% to nearly 90% of total fatty acids in N-limited cultures. Higher biomass and lipid productivity in spring could, partly, be explained by higher irradiance, partly by greater harvesting rate (~30%). Our results indicate the potential for the production of algal high value products (i.e., polyunsaturated fatty acids) during both N-sufficiency and N-limitation. To meet the sustainability challenges of algal biomass production, we propose a dual-system process: Closed photobioreactors producing biomass for high value products and inoculum for larger raceway ponds recycling waste/exhaust streams to produce bulk chemicals for fuel, feed and industrial material.
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| 6. |
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Measurement, Monitoring, Modelling and Control of Bioprocesses
- 2013
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Samlingsverk (redaktörskap) (refereegranskat)abstract
- Automated Measurement and Monitoring of Bioprocesses: Key Elements of the M3C Strategy, by Bernhard Sonnleitner Automatic Control of Bioprocesses, by Marc Stanke, Bernd Hitzmann An Advanced Monitoring Platform for Rational Design of Recombinant Processes, by G. Striedner, K. Bayer Modelling Approaches for Bio-Manufacturing Operations, by Sunil Chhatre Extreme Scale-Down Approaches for Rapid Chromatography Column Design and Scale-Up During Bioprocess Development, by Sunil Chhatre Applying Mechanistic Models in Bioprocess Development, by Rita Lencastre Fernandes, Vijaya Krishna Bodla, Magnus Carlquist, Anna-Lena Heins, Anna Eliasson Lantz, Gürkan Sin and Krist V. Gernaey Multivariate Data Analysis for Advancing the Interpretation of Bioprocess Measurement and Monitoring Data, by Jarka Glassey Design of Pathway-Level Bioprocess Monitoring and Control Strategies Supported by Metabolic Networks, by Inês A. Isidro, Ana R. Ferreira, João J. Clemente, António E. Cunha, João M. L. Dias, Rui Oliveira Knowledge Management and Process Monitoring of Pharmaceutical Processes in the Quality by Design Paradigm, by Anurag S Rathore, Anshuman Bansal, Jaspinder Hans The Choice of Suitable Online Analytical Techniques and Data Processing for Monitoring of Bioprocesses, by Ian Marison, Siobhán Hennessy, Róisín Foley, Moira Schuler, Senthilkumar Sivaprakasam, Brian Freeland
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| 7. |
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| 8. |
- Bonander, Nicklas, 1968, et al.
(författare)
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Optimizing yeast as a host for recombinant protein production
- 2011
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Having access to suitably stable, functional recombinant protein samples underpins diverse academic and industrial research efforts to understand the workings of the cell in health and disease. Synthesizing a protein in recombinant host cells typically allows the isolation of the pure protein in quantities much higher than those found in the protein's native source. Yeast is a popular host as it is a eukaryote with similar synthetic machinery to the native human source cells of many proteins of interest, whilst also being quick, easy and cheap to grow and process. Even in these cells the production of some proteins can be plagued by low functional yields. We have identified molecular mechanisms and culture parameters underpinning high yields and have consolidated our findings to engineer improved yeast cell factories. In this chapter we provide an overview of the opportunities available to improve yeast as a host system for recombinant protein production.
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| 9. |
- Nilsson, Robert, et al.
(författare)
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Techno-economics of carbon preserving butanol production using a combined fermentative and catalytic approach
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 161, s. 263-269
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel process for n-butanol production which combines a fermentation consuming carbon dioxide (succinic acid fermentation) with subsequent catalytic reduction steps to add hydrogen to form butanol. Process simulations in Aspen Plus have been the basis for the techno-economic analyses performed. The overall economy for the novel process cannot be justified, as production of succinic acid by fermentation is too costly. Though, succinic acid price is expected to drop drastically in a near future. By fully integrating the succinic acid fermentation with the catalytic conversion the need for costly recovery operations could be reduced. The hybrid process would need 22% less raw material than the butanol fermentation at a succinic acid fermentation yield of 0.7 g/g substrate. Additionally, a carbon dioxide fixation of up to 13 ktonnes could be achieved at a plant with an annual butanol production of 10 ktonnes
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| 10. |
- Westman, Johan, 1983, et al.
(författare)
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Effects of encapsulation of microorganisms on product formation during microbial fermentations
- 2012
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 96:6, s. 1441-1454
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Forskningsöversikt (refereegranskat)abstract
- This paper reviews the latest developments in microbial products by encapsulated microorganisms in a liquid core surrounded by natural or synthetic membranes. Cells can be encapsulated in one or several steps using liquid droplet formation, pregel dissolving, coacervation, and interfacial polymerization. The use of encapsulated yeast and bacteria for fermentative production of ethanol, lactic acid, biogas, l-phenylacetylcarbinol, 1,3-propanediol, and riboflavin has been investigated. Encapsulated cells have furthermore been used for the biocatalytic conversion of chemicals. Fermentation, using encapsulated cells, offers various advantages compared to traditional cultivations, e.g., higher cell density, faster fermentation, improved tolerance of the cells to toxic media and high temperatures, and selective exclusion of toxic hydrophobic substances. However, mass transfer through the capsule membrane as well as the robustness of the capsules still challenge the utilization of encapsulated cells. The history and the current state of applying microbial encapsulation for production processes, along with the benefits and drawbacks concerning productivity and general physiology of the encapsulated cells, are discussed.
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| 11. |
- Sánchez I Nogué, Violeta, et al.
(författare)
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Isolation and characterization of a resident tolerant Saccharomyces cerevisiae strain from a spent sulfite liquor fermentation plant
- 2012
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Ingår i: AMB Express. - : Springer Science and Business Media LLC. - 2191-0855. ; 2:1, s. 68-
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Tidskriftsartikel (refereegranskat)abstract
- Spent Sulfite Liquor (SSL) from wood pulping facilities is a sugar rich effluent that can be used as feedstock for ethanol production. However, depending on the pulping process conditions, the release of monosaccharides also generates a range of compounds that negatively affect microbial fermentation. In the present study, we investigated whether endogenous yeasts in SSL-based ethanol plant could represent a source of Saccharomyces cerevisiae strains with a naturally acquired tolerance towards this inhibitory environment. Two isolation processes were performed, before and after the re-inoculation of the plant with a commercial baker’s yeast strain. The isolates were clustered by DNA fingerprinting and a recurrent Saccharomyces cerevisiae strain, different from the inoculated commercial baker’s yeast strain, was isolated. The strain, named TMB3720, flocculated heavily and presented high furaldehyde reductase activity. During fermentation of undiluted SSL, TMB3720 displayed a 4-fold higher ethanol production rate and 1.8-fold higher ethanol yield as compared to the commercial baker’s yeast. Another non-Saccharomyces cerevisiae species, identified as the pentose utilizing Pichia galeiformis, was also recovered in the last tanks of the process where the hexose to pentose sugar ratio and the inhibitory pressure are expected to be the lowest.
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| 12. |
- Tomas-Pejo, Elia, 1980, et al.
(författare)
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EVALUATION OF EVOLVED AND BARCODED XYLOSE FERMENTING STRAINS FOR BIOETHANOL PRODUCTION FROM LIGNOCELLULOSE
- 2012
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Ingår i: Science and Technology Day 2012, Chalmers University of Technology, 27th March 2012.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Lignocellulosic raw materials for bioethanol production are today the basis for many ethanol production sites around the world. However, the utilization of engineered yeast strains for second generation ethanol production at large-scale can still be improved. Yeasts mainly use the sugars present in the lignocellulosic biomass but, toxic compounds derived from cellulose, hemicellulose and lignin degradation during pretreatment are also found in the media and inhibit yeast growth. Furthermore, wild type Saccharomyces cerevisiae is not able to ferment xylose which could constitute up to 40% of the lignocellulose material. Hence the recombinant yeast strains must be robust and ferment xylose to ethanol with high yields in the presence of inhibitors.In this study, different evolved xylose fermenting Saccharomyces cerevisiae strains have been compared in ethanol production processes from lignocellulosic hydrolysates. The differences between using single cell transformants and mixed populations will be evaluated in terms of ethanol production in large scale bioreactors.Furthermore, we have established a method to barcode the evolved yeast strains in order to be able to verify their origin. It is of outmost importance that after barcoding the original characteristics of a yeast strain are maintained. Those requirements can only be fulfilled by using a dominant selection principle. We have obtained a few hundred transformants that were shown to contain the new unique barcode DNA sequence via DNA isolation and DNA sequencing. The transformed strains must be able to grow on the lignocellulosic material and consume xylose at the same rate as before the transformation which also was tested in this study.
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| 13. |
- Martinez Avila, Hector, 1985, et al.
(författare)
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Biocompatibility evaluation of densified bacterial nanocellulose hydrogel as an implant material for auricular cartilage regeneration
- 2014
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 98:17, s. 7423-7435
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial nanocellulose (BNC), synthesized by the bacterium Gluconacetobacter xylinus, is composed of highly hydrated fibrils (99 % water) with high mechanical strength. These exceptional material properties make BNC a novel biomaterial for many potential medical and tissue engineering applications. Recently, BNC with cellulose content of 15 % has been proposed as an implant material for auricular cartilage replacement, since it matches the mechanical requirements of human auricular cartilage. This study investigates the biocompatibility of BNC with increased cellulose content (17 %) to evaluate its response in vitro and in vivo. Cylindrical BNC structures (48 Au 20 mm) were produced, purified in a built-in house perfusion system, and compressed to increase the cellulose content in BNC hydrogels. The reduction of endotoxicity of the material was quantified by bacterial endotoxin analysis throughout the purification process. Afterward, the biocompatibility of the purified BNC hydrogels with cellulose content of 17 % was assessed in vitro and in vivo, according to standards set forth in ISO 10993. The endotoxin content in non-purified BNC (2,390 endotoxin units (EU)/ml) was reduced to 0.10 EU/ml after the purification process, level well below the endotoxin threshold set for medical devices. Furthermore, the biocompatibility tests demonstrated that densified BNC hydrogels are non-cytotoxic and cause a minimal foreign body response. In support with our previous findings, this study concludes that BNC with increased cellulose content of 17 % is a promising non-resorbable biomaterial for auricular cartilage tissue engineering, due to its similarity with auricular cartilage in terms of mechanical strength and host tissue response.
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| 14. |
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| 15. |
- Bergenholtz, Sa Schoug, et al.
(författare)
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A case study on stress preconditioning of a Lactobacillus strain prior to freeze-drying
- 2012
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Ingår i: Cryobiology. - : Elsevier BV. - 0011-2240 .- 1090-2392. ; 64:3, s. 152-159
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Tidskriftsartikel (refereegranskat)abstract
- Freeze-drying of bacterial cells with retained viability and activity after storage requires appropriate formulation, i.e. mixing of physiologically adapted cell populations with suitable protective agents, and control of the freeze-drying process. Product manufacturing may alter the clinical effects of probiotics and it is essential to identify and understand possible factor co-dependencies during manufacturing. The physical solid-state behavior of the formulation and the freeze-drying parameters are critical for bacterial survival and thus process optimization is important, independent of strain. However, the maximum yield achievable is also strain-specific and strain survival is governed by e.g. medium, cell type, physiological state, excipients used, and process. The use of preferred compatible solutes for cross-protection of Lactobacilli during industrial manufacturing may be a natural step to introduce robustness, but knowledge is lacking on how compatible solutes, such as betaine, influence formulation properties and cell survival. This study characterized betaine formulations, with and without sucrose, and tested these with the model lactic acid bacteria Lactobacillus coryniformis Si3. Betaine alone did not act as a lyo-protectant and thus betaine import prior to freeze-drying should be avoided. Differences in protective agents were analyzed by calorimetry, which proved to be a suitable tool for evaluating the characteristics of the freeze-dried end products.
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| 16. |
- Janssen, Mathias, 1973, et al.
(författare)
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Influence of high gravity process conditions on the environmental impact of ethanol production from wheat straw
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 173, s. 148-158
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Tidskriftsartikel (refereegranskat)abstract
- Biofuel production processes at high gravity are currently under development. Most of these processes however use sugars or first generation feedstocks as substrate. This paper presents the results of a life cycle assessment (LCA) of the production of bio-ethanol at high gravity conditions from a second generation feedstock, namely, wheat straw. The LCA used lab results of a set of 36 process configurations in which dry matter content, enzyme preparation and loading, and process strategy were varied. The LCA results show that higher dry matter content leads to a higher environmental impact of the ethanol production, but this can be compensated by reducing the impact of enzyme production and use, and by polyethylene glycol addition at high dry matter content. The results also show that the renewable and non-renewable energy use resulting from the different process configurations ultimately determine their environmental impact.
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| 17. |
- Mesfun, Sennai, et al.
(författare)
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Black liquor fractionation for biofuels production : A techno-economic assessment
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 166, s. 508-517
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Tidskriftsartikel (refereegranskat)abstract
- The hemicelluloses fraction of black liquor is an underutilized resource in many chemical pulp mills. It is possible to extract and separate the lignin and hemicelluloses from the black liquor and use the hemicelluloses for biochemical conversion into biofuels and chemicals. Precipitation of the lignin from the black liquor would consequently decrease the thermal load on the recovery boiler, which is often referred to as a bottleneck for increased pulp production. The objective of this work is to techno-economically evaluate the production of sodium-free lignin as a solid fuel and butanol to be used as fossil gasoline replacement by fractionating black liquor. The hydrolysis and fermentation processes are modeled in Aspen Plus to analyze energy and material balances as well as to evaluate the plant economics. A mathematical model of an existing pulp and paper mill is used to analyze the effects on the energy performance of the mill subprocesses.
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| 18. |
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| 19. |
- Nordgren, Daniel, et al.
(författare)
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Ash transformations in pulverised fuel co-combustion of straw and woody biomass
- 2013
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Ingår i: Fuel processing technology. - : Elsevier BV. - 0378-3820 .- 1873-7188. ; 105, s. 52-58
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Tidskriftsartikel (refereegranskat)abstract
- Ash transformation processes have been studied during co-firing of wheat straw and pine stem wood and softwood bark. Pilot-scale trials in a 150kW pulverised-fuel-fired burner were performed. Thermodynamic equilibrium calculations were made to support the interpretation of the results. The results show that reactions involving condensed phases are kinetically limited compared to reactions between gaseous ash compounds. Accordingly, the conditions promote gas phase reactions resulting in the formation of chlorides, sulphates and carbonates whereas reactions involving condensed reactants are suppressed. Both the slagging and fouling propensities of all co-firing mixes were reduced compared to that for pure straw. For the wood/straw mixes this was mainly due to a dilution of the ash forming elements of straw whereas for straw/bark, an additional effect from interaction between the fuel ash components was observed to reduce slagging. In general it can be concluded that under powder combustion conditions equilibrium is approached selectively and that the ash matter is strongly fractionated. The general results in this paper are useful for straw-fired power stations looking for alternative co-firing fuels.
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| 20. |
- Mayers, Joshua, 1988, et al.
(författare)
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Influence of the N: P supply ratio on biomass productivity and time-resolved changes in elemental and bulk biochemical composition of Nannochloropsis sp.
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 169, s. 588-595
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Tidskriftsartikel (refereegranskat)abstract
- This work reports for the first time the detailed impacts of dual nitrogen (N) and phosphorus (P) stress on growth dynamics and biochemical composition in the Eustigmatophyte Nannochloropsis sp. P-stress concurrent with N-stress had subtle effects on culture bulk biochemical composition, but negatively influenced biomass productivity. However, the N:P supply ratio can be raised to at least 32:1 without compromising productivity (yielding a maximum lipid content of 52% of dry weight and volumetric lipid concentration of 233mgL-1). The maximum biomass and lipid yields per unit of cell-P were 1.2kgDW (gP)-1 and 0.54kglipid (gP)-1. The P concentration of many common media is thus in surplus for optimal Nannochloropsis sp. biomass and lipid production, offering potential for significant savings in P usage and improving the sustainability of algal cultivation. © 2014 Elsevier Ltd.
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| 21. |
- Anasontzis, George E, 1980, et al.
(författare)
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Constitutive homologous expression of phosphoglucomutase and transaldolase increases the metabolic flux of Fusarium oxysporum
- 2014
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Ingår i: Microbial Cell Factories. - : Springer Science and Business Media LLC. - 1475-2859. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Fusarium oxysporum is among the few filamentous fungi that have been reported of being able to directly ferment biomass to ethanol in a consolidated bioprocess. Understanding its metabolic pathways and their limitations can provide some insights on the genetic modifications required to enhance its growth and subsequent fermentation capability. In this study, we investigated the hypothesis reported previously that phosphoglucomutase and transaldolase are metabolic bottlenecks in the glycolysis and pentose phosphate pathway of the F. oxysporum metabolism.Results: Both enzymes were homologously overexpressed in F. oxysporum F3 using the gpdA promoter of Aspergillus nidulans for constitutive expression. Transformants were screened for their phosphoglucomutase and transaldolase genes expression levels with northern blot. The selected transformant exhibited high mRNA levels for both genes, as well as higher specific activities of the corresponding enzymes, compared to the wild type. It also displayed more than 20 and 15% higher specific growth rate upon aerobic growth on glucose and xylose, respectively, as carbon sources and 30% higher biomass to xylose yield. The determination of the relative intracellular amino and non-amino organic acid concentrations at the end of growth on glucose revealed higher abundance of most determined metabolites between 1.5- and 3-times in the recombinant strain compared to the wild type. Lower abundance of the determined metabolites of the Krebs cycle and an 68-fold more glutamate were observed at the end of the cultivation, when xylose was used as carbon source.Conclusions: Homologous overexpression of phosphoglucomutase and transaldolase in F. oxysporum was shown to enhance the growth characteristics of the strain in both xylose and glucose in aerobic conditions. The intracellular metabolites profile indicated how the changes in the metabolome could have resulted in the observed growth characteristics. © 2014 Anasontzis et al.; licensee BioMed Central Ltd.
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| 22. |
- Faisal, Abrar, et al.
(författare)
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MFI zeolite as adsorbent for selective recovery of hydrocarbons from ABE fermentation broths
- 2014
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Ingår i: Adsorption. - : Springer Science and Business Media LLC. - 0929-5607 .- 1572-8757. ; 20:2-3, s. 465-470
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Tidskriftsartikel (refereegranskat)abstract
- 1-Butanol and butyric acid are two interesting compounds that may be produced by acetone, butanol, and ethanol fermentation using e.g. Clostridium acetobutylicum. The main drawback, restricting the commercialization potential of this process, is the toxicity of butanol for the cell culture resulting in low concentrations of this compound in the broth. To make this process economically viable, an efficient recovery process has to be developed. In this work, a hydrophobic MFI type zeolite with high silica to alumina ratio was evaluated as adsorbent for the recovery of butanol and butyric acid from model solutions. Dual component adsorption experiments revealed that both butanol and butyric acid showed a high affinity for the hydrophobic MFI zeolite when adsorbed from aqueous model solutions. Multicomponent adsorption experiments using model solutions, mimicking real fermentation broths, revealed that the adsorbent was very selective to the target compounds. Further, the adsorption of butyric and acetic acid was found to be pH dependent with high adsorption below, and low adsorption above, the respective pKa values of the acids. Thermal desorption of butanol from MFI type zeolite was also studied and a suitable desorption temperature was identified.
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| 23. |
- Janssen, Mathias, 1973, et al.
(författare)
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Simulation and LCA of a bioethanol process technology in development
- 2013
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Ingår i: Proceedings of the 7th International Society for Industrial Ecology Biennial Conference.
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Konferensbidrag (refereegranskat)abstract
- The development of sustainable processes for the production of second generation biofuels is an ongoing effort. Not only does such a process need to be economically feasible, it should also produce a biofuel that has a lower environmental impact compared to first generation biofuels or fossil fuels. In this work, Life cycle assessment (LCA) is used for the evaluation of such a process along its development path. The objectives of this evaluation are to help improve and/or optimize the process in development from an environmental perspective and to help guide this development. In particular, the process under study uses high-gravity fermentation, i.e. a process with a high solids concentration in the fermentation reactor, for the production of ethanol from wood and straw. A simulation model of a plant with an industrially relevant capacity using the high-gravity technology has been set up in order to address issues of scaling up the process in development (process-level scale). Data from lab experiments are used by this model and the simulation results are subsequently used in the LCA model in order to calculate the environmental impact of the technology at an industrial scale. Furthermore, the scale at which biofuels are applied in land transport, partly due to targets set in e.g. the EU Renewable Energy Directive, needs to be accounted for (biofuel sector-level scale). The consequent feedstock use, and resulting land use and land use change impacts, as well as biogenic carbon emissions need to be included in the LCA. This paper discusses the modeling at the aforementioned process level and results are presented in order to demonstrate the importance of considering scale issues at this level. The inclusion of scale issues at the biofuel sector level in LCA will be discussed.
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- Tomas-Pejo, Elia, 1980, et al.
(författare)
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Effect of inhibitors present n lignocellulosic hydrolysates on evolved xylose fermenting Saccharomyces cerevisiae strains
- 2012
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Ingår i: 34th Symposium for Biofuels and Chemicals. New Orleans, USA. 30th April – 3rd May 2012.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The development of inhibitor tolerant ethanologenic yeasts is one of the important challenges for a successful bioethanol production process from lignocellulose. Furthermore, an efficient microorganism for bioethanol production has to be able to ferment xylose together with glucose since xylose represents a large fraction in the lignocellulosic biomass. Weak acids and phenolic compounds are some of the prevalent inhibitors generated during pretreatment of lignocellulose and they will be present in the fermentation broth stressing the yeast affecting the fermentation performance. Although some studies on the effect of organic acids on fermenting microorganisms have been published, there is a lack of knowledge on the effect of phenolic compounds on yeast and more concretely about the effect on the xylose fermentation performance. In this study, the effect of acetic acid and vanillin on yeast growth on glucose and xylose will be elucidated using synthetic media mimicking lignocellulosic hydrolysates. It is known that one of general stress responses in yeast is the accumulation and mobilization of energy reserves (trehalose and glycogen). Trehalose protects cells from damage, increasing cell viability, however, when inhibitors are present in the media the trehalose synthesis and degradation could be affected. Furthermore differences in gene expression of key genes involved in acetic acid and vanillin tolerance and xylose fermentation will be studied. In this work we will also compare different evolved strains and evaluate mixed populations compared to single clones, in terms of trehalose and glycogen content and inhibitor tolerance.
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