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- Horváth, I. S., et al.
(författare)
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Effects of furfural on anaerobic continuous cultivation of Saccharomyces cerevisiae
- 2001
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 0006-3592 .- 1097-0290. ; 75:5, s. 540-549
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Tidskriftsartikel (refereegranskat)abstract
- Furfural is an important inhibitor of yeast metabolism in lignocellulose-derived substrates. The effect of furfural on the physiology of Saccharomyces cerevisiae CBS 8066 was investigated using anaerobic continuous cultivations. Experiments were performed with furfural in the feed medium (up to 8.3 g/L) using three dierent dilution rates (0.095, 0.190, and 0.315 h-1). The measured concentration of furfural was low (<0.1 g/L) at all steady states obtained. However, it was not possible to achieve a steady state at a specific conversion rate of furfural, qf, higher than approximately 0.15 g/g·h. An increased furfural concentration in the feed caused a decrease in the steady-state glycerol yield. This agreed well with the decreased need for glycerol production as a way to regenerate NAD+, i.e., to function as a redox sink because furfural was reduced to furfuryl alcohol. Transient experiments were also performed by pulse addition of furfural directly into the fermentor. In contrast to the situation at steady-state conditions, both glycerol and furfuryl alcohol yields increased after pulse addition of furfural to the culture. Furthermore, the maximum specific conversion rate of furfural (0.6 g/g·h) in dynamic experiments was significantly higher than what was attainable in the chemostat experiments. The dynamic furfural conversion could be described by the use of a simple Michaelis-Menten-type kinetic model. Also furfural conversion under steady-state conditions could be explained by a Michaelis-Menten-type kinetic model, but with a higher anity and a lower maximum conversion rate. This indicated the presence of an additional component with a higher anity, but lower maximum capacity, either in the transport system or in the conversion system of furfural.
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| 2. |
- Horvath, I. S., et al.
(författare)
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Selection of anion exchangers for detoxification of dilute-acid hydrolysates from spruce
- 2004
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Ingår i: Applied Biochemistry and Biotechnology. - 0273-2289 .- 1559-0291. ; 113, s. 525-538
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Tidskriftsartikel (refereegranskat)abstract
- Six anion-exchange resins with different properties were compared with respect to detoxification of a dilute-acid hydrolysate of spruce prior to ethanolic fermentation with Saccharomyces cerevisiae. The six resins encompassed strong and weak functional groups as well as styrene-, phenol-, and acrylic-based matrices. In an analytical experimental series, fractions from columns packed with the different resins were analyzed regarding pH, glucose, furfural, hydroxymethylfurfural, phenolic compounds, levulinic acid, acetic acid, formic acid, and sulfate. An initial adsorption of glucose occurred in the strong alkaline environment and led to glucose accumulation at a later stage. Acetic and levulinic acid passed through the column before formic acid, whereas sulfate had the strongest affinity. In a preparative experimental series, one fraction from each of six columns packed with the different resins was collected for assay of the fermentability and analysis of glucose, mannose, and fermentation inhibitors. The fractions collected from strong anion-exchange resins with styrene-based matrices displayed the best fermentability: a sevenfold enhancement of ethanol productivity compared with untreated hydrolysate. Fractions from a strong anion exchanger with acrylic-based matrix and a weak exchanger with phenol-based resin displayed an intermediate improvement in fermentability, a four- to fivefold increase in ethanol productivity. The fractions from two weak exchangers with styrene- and acrylic-based matrices displayed a twofold increase in ethanol productivity. Phenolic compounds were more efficiently removed by resins with styrene- and phenol-based matrices than by resins with acrylic-based matrices.
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| 3. |
- Horvath, ZJ, et al.
(författare)
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Electrical peculiarities in Al/Si/Ge/... /Ge/Si and Al/SiGe/Si structures
- 2002
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 190:1-4, s. 403-407
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Tidskriftsartikel (refereegranskat)abstract
- The current-voltage (I-V) and capacitance-voltage (C-V) behaviour of different Si/Ge multilayers and SiGe single layers prepared on p-type Si substrates by magnetron sputtering and annealing, has been studied in the temperature rang, of 80-320 K by using Al Schottky contacts as test structures. Although a significant influence of the microstructure of the Si/Ge multilayers and SiGe layers was obtained on the electrical behaviour of the structures, the structures exhibited similar specific features. (C) 2002 Elsevier Science B.V. All rights reserved.
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