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  • 51.
    Teghammar, Anna
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Karimi, Keikhosro
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Sárvári Horváth, Ilona
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Saddler, Jack
    Taherzadeh, Mohammad
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Pretreatment of soft wood spruce and triticale straw by NMMO for enhanced biogas production2010Konferensbidrag (Övrigt vetenskapligt)
  • 52.
    Westman, Johan
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ethanol production from lignocellulose using high local cell density yeast cultures. Investigations of flocculating and encapsulated Saccharomyces cerevisiae2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Efforts are made to change from 1st to 2nd generation bioethanol production, using lignocellulosics as raw materials rather than using raw materials that alternatively can be used as food sources. An issue with lignocellulosics is that a harsh pretreatment step is required in the process of converting them into fermentable sugars. In this step, inhibitory compounds such as furan aldehydes and carboxylic acids are formed, leading to suboptimal fermentation rates. Another issue is that lignocellulosics may contain a large portion of pentoses, which cannot be fermented simultaneously with glucose by Saccharomyces cerevisiae. In this thesis, high local cell density has been investigated as a means of overcoming these two issues. Encapsulation of yeast in semi-permeable alginate-chitosan capsules increased the tolerance towards furan aldehydes, but not towards carboxylic acids. The selective tolerance can be explained by differences in the concentration of compounds radially through the cell pellet inside the capsule. For inhibitors, gradients will only be formed if the compounds are readily convertible, like the furan aldehydes. Conversion of inhibitors by cells close to the membrane leads to decreased concentrations radially through the cell pellet. Thus, cells closer to the core experience subinhibitory levels of inhibitors and can ferment sugars. Carbohydrate gradients also give rise to nutrient limitations, which in turn trigger a stress response in the yeast, as was observed on mRNA and protein level. The stress response is believed to increase the robustness of the yeast and lead to improved tolerance towards additional stress. Glucose and xylose co-consumption by a recombinant strain, CEN.PK XXX, was also improved by encapsulation. Differences in affinity of the sugar transporters normally result in that glucose is taken up preferentially to xylose. However, when encapsulated, cells in different parts of the capsule experienced high and low glucose concentrations simultaneously. Xylose and glucose could thus be taken up concurrently. This improved the co-utilisation of the sugars by the system and led to 50% higher xylose consumption and 15% higher final ethanol titres. A protective effect by the capsule membrane itself could not be shown. Hence, the interest in flocculation was triggered, as a more convenient way to keep the cells together. To investigate whether flocculation increases the tolerance, like encapsulation, recombinant flocculating yeast strains were constructed and compared with the non-flocculating parental strain. Experiments showed that strong flocculation did not increase the tolerance towards carboxylic acids. However, the tolerance towards a spruce hydrolysate and especially against furfural was indeed increased. The results of this thesis show that high local cell density yeast cultures have the potential to aid against two of the major problems for 2nd generation bioethanol production: inhibitors and simultaneous hexose and pentose utilisation.

  • 53.
    Westman, Johan
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Mapelli, Valeria
    Taherzadeh, Mohammad
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzén, Carl Johan
    High local cell density for efficient 2nd generation bioethanol production by Saccharomyces cerevisiae2013Konferensbidrag (Övrigt vetenskapligt)
  • 54.
    Westman, Johan
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Mapelli, Valeria
    Taherzadeh, Mohammad
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzén, Carl Johan
    Together we are strong: Yeast flocculation for efficient fermentation of toxic hydrolysates2013Konferensbidrag (Övrigt vetenskapligt)
  • 55.
    Westman, Johan O.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Together we are strong! Second generation bioethanol production by flocculating and encapsulated yeast2011Konferensbidrag (Övrigt vetenskapligt)
  • 56.
    Westman, Johan O.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Babikondu, Ramesh Babu
    Franzén, Carl Johan
    Taherzadeh, Mohammad J
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Encapsulation-Induced Stress Helps Saccharomyces cerevisiae Resist Convertible Lignocellulose Derived Inhibitors2012Ingår i: International Journal of Molecular Sciences, ISSN 1422-0067, E-ISSN 1422-0067, Vol. 13, nr 9, s. 11881-11894Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ability of macroencapsulated Saccharomyces cerevisiae CBS8066 to withstand readily and not readily in situ convertible lignocellulose-derived inhibitors was investigated in anaerobic batch cultivations. It was shown that encapsulation increased the tolerance against readily convertible furan aldehyde inhibitors and to dilute acid spruce hydrolysate, but not to organic acid inhibitors that cannot be metabolized anaerobically. Gene expression analysis showed that the protective effect arising from the encapsulation is evident also on the transcriptome level, as the expression of the stress-related genes YAP1, ATR1 and FLR1 was induced upon encapsulation. The transcript levels were increased due to encapsulation already in the medium without added inhibitors, indicating that the cells sensed low stress level arising from the encapsulation itself. We present a model, where the stress response is induced by nutrient limitation, that this helps the cells to cope with the increased stress added by a toxic medium, and that superficial cells in the capsules degrade convertible inhibitors, alleviating the inhibition for the cells deeper in the capsule.

  • 57.
    Westman, Johan O.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzen, CJ
    Taherzadeh, Mohammad
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Characterization of Domsjö flocculating yeast strain2009Konferensbidrag (Övrigt vetenskapligt)
  • 58.
    Westman, Johan O.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzén, Carl Johan
    Taherzadeh, Mohammad J.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Phenotypical and Physiological Characterization of a Flocculating Yeast Strain2010Konferensbidrag (Övrigt vetenskapligt)
  • 59.
    Westman, Johan O.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Taherzadeh, Mohammad J
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzén, Car Johan
    Encapsulated vs. free yeast: A comparative proteomic study2011Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    In the search for a replacement for fossil fuels, due to their depletion as well as an increased concern about our environment, 2nd generation bioethanol comes out as one of the most promising alternatives. There are challenges in several steps of lignocellulose processing – especially due to the formation of for yeast inhibitory compounds during pretreatment and hydrolysis. It has previously been shown that encapsulation of the yeast in membranes made of an alginate gel enables the yeast to survive otherwise toxic hydrolysates. The physiological changes arising from encapsulation are however largely unknown, although it has been shown that the macromolecular composition of the yeast changes during prolonged cultivation. In this study we have therefore performed a comparative proteomic study of yeast grown in capsules and in suspension in anaerobic batch cultivations.

  • 60.
    Westman, Johan O.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Taherzadeh, Mohammad J
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzén, Carl Johan
    Inhibitor tolerance and flocculation: Characterization of a yeast strain suitable for 2nd generation bioethanol production2011Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Robust second generation bioethanol processes require microorganisms able to obtain high yields and production rates while fermenting inhibiting hydrolysates. However, tolerance towards inhibitors like, carboxylic acids, furan aldehydes and phenolic compounds, is still an issue and the factors contributing to improved tolerance are not well known. In this study, the constitutively flocculating Saccharomyces cerevisiae strain CCUG 53310, with good ability to ferment toxic hydrolysates, was compared with S. cerevisiae CBS 8066 in order to characterize the mechanisms of flocculation and the fermentative performance in different inhibitory media. The flocculation of CCUG 53310 depended on cell wall proteins and was partly inhibited by mannose. The flocculating cells also exhibited a significantly higher hydrophobicity than the cells of the non-flocculating strain CBS 8066, which might contribute to the flocculation. The flocculating strain was more tolerant to carboxylic acids and furan aldehydes, but more sensitive to phenolic compounds. Surprisingly, the expression increase of YAP1, ATR1 and FLR1, known to confer resistance against lignocellulose-derived inhibitors, upon addition of various inhibitors to the fermentation medium, was less in CCUG 53310 than in CBS 8066 in most cases. This indicates that the flocculating strain experienced the cultivation conditions as less stressful. The flocculation in itself is a likely cause of this by creating subinhibitory local levels of inhibitors for most cells, allowing the cells in flocs to experience a lower collective stress level.

  • 61.
    Westman, Johan O.
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Talebnia, Farid
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzén, Carl Johan
    Taherzadeh, Mohammad J.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Together we are strong! Inhibitor tolerance conferred by good neighbors?2010Konferensbidrag (Övrigt vetenskapligt)
  • 62.
    Wikandari, Rachma
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Effect of fruit flavors on anaerobic digestion: inhibitions and solutions2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Fruits are among the most important commodities in global trading due to its fundamental nutritional values. In 2012, the fruits supply was 115 kg/person/year, however, only 50 % of the fruits reached their consumers and the rest ended up as waste during the long fruit supply chain. The waste from fruits is mostly dumped or burned, creating a serious environmental problem. A more sustainable handling of the waste is therefore highly desirable. One of them is conversion of the fruits wastes into biogas through anaerobic digestion. One challenge with the conversion of fruits wastes into biogas is the presence of antimicrobial compounds in the fruits, which reduce the biogas yield or even cause a total failure of the process. Fruit flavors have been reported to have antimicrobial activity against several microorganisms and being responsible for the defense system in the fruits. However, there is only scarce information about the effect of fruit flavors on anaerobic digesting microbia. The objectives of the present thesis were: 1) to investigate the inhibitory activity of the fruit flavors on anaerobic digestion; 2) to remove the flavor compound by pretreatment; and 3) to protect the cell from the flavor compounds using a membrane bioreactor. The inhibitory activity of the fruit flavors was examined from different groups of flavors by adding a single flavor compound into the batch anaerobic digesting system, at three different concentrations. Among the flavors added, myrcene and octanol were found to exhibit a strong inhibitory activity, with 50 % reduction of the methane production at low concentrations, ca. 0.005–0.05 %. These flavors can be found in oranges, strawberries, grapes, plums, and mangoes. The other flavors tested showed moderate and low inhibitory activity, which might not affect the anaerobic digestion of the fruits wastes. In order to overcome the inhibitory effects of the fruit flavor, two approaches were proposed in this thesis, namely, fruit flavor removal by leaching pretreatment and cell protection from fruit flavor using a membrane bioreactor. Orange peel waste and D-limonene were used as a model of fruit waste and inhibitor, respectively. The leaching pretreatment uses solvent to extract the limonene from the orange peel. The methane yield increased by 356 % from 0.061 Nm3/kg VS to 0.217 Nm3/kg VS, by pretreating the peel using hexane with peel and a hexane ratio of 1:12 at room temperature for 10 min. Alternative to limonene removal, the cells were encased in a hydrophilic membrane, which is impermeable to hydrophobic limonene. This method yielded more than six times higher methane yield, compared to the free cell. At the highest organic loading rate, examined in this work, 3 g VS/L/day, the methane yield of the reactor containing the free cell was only 0.05 Nm3/kg VS, corresponding to 10 % of the theoretical yield, whereas 0.33 Nm3/kg VS methane yield was achieved using a membrane bioreactor corresponding to 75 % of the theoretical yield.

  • 63.
    Ylitervo, Päivi
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Concepts for improving ethanol productivity from lignocellulosic materials: encapsulated yeast and membrane bioreactors2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    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.

  • 64.
    Ylitervo, Päivi
    et al.
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Franzen, CJ
    Taherzadeh, Mohammad
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Ethanol production from lignocellulosic raw materials by encapsulated Saccharomyces cerevisiae2009Konferensbidrag (Övrigt vetenskapligt)
  • 65.
    Zamani, Akram
    Högskolan i Borås, Institutionen Ingenjörshögskolan.
    Superabsorbent Polymers from the Cell Wall of Zygomycetes Fungi2010Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    The present thesis presents new renewable, antimicrobial and biodegradable superabsorbent polymers (SAPs), produced from the cell wall of zygomycetes fungi. The cell wall was characterized and chitosan, being one of the most important ingredients, was extracted, purified, and converted to SAP for use in disposable personal care products designed for absorption of different body fluids. The cell wall of zygomycetes fungi was characterized by subsequent hydrolysis with sulfuric and nitrous acids and analyses of the products. The main ingredients of the cell wall were found to be polyphosphates (4-20%) and copolymers of glucosamine and N-acetyl glucosamine, i.e. chitin and chitosan (45-85%). The proportion of each of these components was significantly affected by the fungal strain and also the cultivation conditions. Moreover, dual functions of dilute sulfuric acid in relation to chitosan, i.e. dissolution at high temperatures and precipitation at lowered temperatures, were discovered and thus used as a basis for development of a new method for extraction and purification of the fungal chitosan. Treatment of the cell wall with dilute sulfuric acid at room temperature resulted in considerable dissolution of the cell wall polyphosphates, while chitosan and chitin remained intact in the cell wall residue. Further treatment of this cell wall residue, with fresh acid at 120°C, resulted in dissolution of chitosan and its separation from the remaining chitin/chitosan of the cell wall skeleton which was not soluble in hot acid. Finally, the purified fungal chitosan (0.34 g/g cell wall) was recovered by precipitation at lowered temperatures and pH 8-10. The purity and the yield of fungal chitosan in the new method were significantly higher than that were obtained in the traditional acetic acid extraction method. As a reference to pure chitosan, SAP from shellfish chitosan, was produced by conversion of this biopolymer into water soluble carboxymethyl chitosan (CMCS), gelation of CMCS with glutaraldehyde in aqueous solutions (1-2%), and drying the resultant gel. Effects of carboxymethylation, gelation and drying conditions on the water binding capacity (WBC) of the final products, were investigated. Finally, choosing the best condition, a biological superabsorbent was produced from zygomycetes chitosan. The CMCS-based SAPs were able to absorb up to 200 g water/g SAP. The WBC of the best SAP in urine and saline solutions was 40 and 32 g/g respectively, which is comparable to the WBC of commercially acceptable SAPs under identical conditions (34-57 and 30-37 g/g respectively).

12 51 - 65 av 65
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