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  • 1.
    Lennartsson, Patrik
    et al.
    University of Borås, School of Engineering.
    Karimi, Keikhosro
    University of Borås, School of Engineering.
    Edebo, Lars
    Taherzadeh, Mohammad
    University of Borås, School of Engineering.
    Effects of different growth forms of Mucor indicus on cultivation on dilute-acid lignocellulosic hydrolyzate, inhibitor tolerance, and cell wall composition2009In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 143, no 4, p. 225-261Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Nilsson, A.
    et al.
    Department of Chemical Engineering II, Lund University of Technology.
    Taherzadeh, Mohammad J
    Department of Chemical Engineering II, Lund University of Technology.
    Lidén, G.
    Department of Chemical Engineering II, Lund University of Technology.
    Use of dynamic step response for control of fed-batch conversion of lignocellulosic hydrolyzates to ethanol2001In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 89, no 1, p. 41-53Article in journal (Refereed)
    Abstract [en]

    Optimization of fed-batch conversion of lignocellulosic hydrolyzates by the yeast Saccharomyces cerevisiae was studied. The feed rate was controlled using a step response strategy, in which the carbon dioxide evolution rate was used as input variable. The performance of the control strategy was examined using both an untreated and a detoxified dilute acid hydrolyzate, and the performance was compared to that obtained with a synthetic medium. In batch cultivation of the untreated hydrolyzate, only 23% of the hexose sugars were assimilated. However, by using the feed-back controlled fed-batch technique, it was possible to obtain complete conversion of the hexose sugars. Furthermore, the maximal specific ethanol productivity (qE, max) increased more than 10-fold, from 0.06 to 0.70 g g-1 h-1. In addition, the viability of the yeast cells decreased by more than 99% in batch cultivation, whereas a viability of more than 40% could be maintained during fed-batch cultivation. In contrast to untreated hydrolyzate, it was possible to convert the sugars in the detoxified hydrolyzate also in batch cultivation. However, a 50% higher specific ethanol productivity was obtained using fed-batch cultivation. During batch cultivation of both untreated and detoxified hydrolyzate a gradual decrease in specific ethanol productivity was observed. This decrease could largely be avoided in fed-batch cultivations.

  • 3.
    Purwadi, R.
    et al.
    Dept. Chem. Eng. and Environ. Sci., Chalmers University of Technology.
    Niklasson, C.
    Dept. Chem. Eng. and Environ. Sci., Chalmers University of Technology.
    Taherzadeh, Mohammad J
    Dept. Chem. Eng. and Environ. Sci., Chalmers University of Technology.
    Kinetic study of detoxification of dilute-acid hydrolyzates by Ca(OH) 22004In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 114, no 1-2, p. 187-198Article in journal (Refereed)
    Abstract [en]

    Detoxification of dilute-acid hydrolyzates by addition of Ca(OH) 2 (overliming) and cultivation of the detoxified hydrolyzates by Saccharomyces cerevisiae were examined. The examined overliming involves increasing the pH of the hydrolyzates to 9, 10, 11 or 12, keeping up to 90 min at different temperatures of 30, 45 and 60°C, followed by readjustment of the pH to 5. Increasing the pH, time and/or temperature resulted in more effective degradation of furans and resulted in better fermentability for both of the tested hydrolyzates, but higher loss of the sugars was observed as well. Overliming of glucose and furfural solution at pH 12 showed a rapid decrease in concentration of these chemicals followed by a slow degradation process. Therefore, a kinetic model was proposed for the detoxification, where the sugars or furans make transient complexes with calcium ions and this complex will then be converted to the degradation product. The ANOVA analysis of the model resulted in an average R 2 of 0.99 for the model fitted to all the experimental data points.

  • 4.
    Talebnia, F.
    et al.
    Chalmers University of Technology.
    Taherzadeh, Mohammad J
    University of Borås, Faculty of Textiles, Engineering and Business.
    In situ detoxification and continuous cultivation of dilute-acid hydrolyzate to ethanol by encapsulated S. cerevisiae2006In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 125, no 3, p. 377-384Article in journal (Refereed)
    Abstract [en]

    Dilute-acid lignocellulosic hydrolyzate was successfully fermented to ethanol by encapsulated Saccharomyces cerevisiae at dilution rates up to 0.5 h-1. The hydrolyzate was so toxic that freely suspended yeast cells could ferment it continuously just up to dilution rate 0.1 h-1, where the cells lost 75% of their viability measured by colony forming unit (CFU). However, encapsulation increased their capacity for in situ detoxification of the hydrolyzate and protected the cells against the inhibitors present in the hydrolyzate. While the cells were encapsulated, they could successfully ferment the hydrolyzate at tested dilution rates 0.1-0.5 h-1, and keep more than 75% cell viability in the worst conditions. They produced ethanol with yield 0.44 ± 0.01 g/g and specific productivity 0.14-0.17 g/(g h) at all dilution rates. Glycerol was the main by-product of the cultivations, which yielded 0.039-0.052 g/g. HMF present in the hydrolyzate was converted 48-71% by the encapsulated yeast, while furfural was totally converted at dilution rates 0.1 and 0.2 h-1 and partly at the higher rates. Continuous cultivation of encapsulated yeast was also investigated on glucose in synthetic medium up to dilution rate 1.0 h-1. At this highest rate, ethanol and glycerol were also the major products with yields 0.43 and 0.076 g/g, respectively. The experiments lasted for 18-21 days, and no damage in the capsules was detected. 

  • 5. Ylitervo, Päivi
    et al.
    Franzen, Carl Johan
    Taherzadeh, Mohammad J.
    University of Borås, School of Engineering.
    Ethanol production at elevated temperatures using encapsulation of yeast2011In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 156, no 1, p. 22-29Article in journal (Refereed)
    Abstract [en]

    The ability of macroencapsulated Saccharomyces cerevisiae CBS 8066 to produce previous termethanolnext term at previous termelevatednext termprevious termtemperaturesnext term was investigated in consecutive batch and continuous cultures. Prior to cultivation previous termyeastnext term was confined inside alginate–chitosan capsules composed of an outer semi-permeable membrane and an inner liquid core. The encapsulated previous termyeastnext term could successfully ferment 30 g/L glucose and produce previous termethanolnext term at a high yield in five consecutive batches of 12 h duration at 42 °C, while freely suspended previous termyeastnext term was completely inactive already in the third batch. A high previous termethanolnext termprevious termproductionnext term was observed also through the first 48 h at 40 °C during continuous cultivation at D = 0.2 h−1 when using encapsulated cells. The previous termethanolnext termprevious termproductionnext term slowly decreased in the following days at 40 °C. The previous termethanolnext termprevious termproductionnext term was also measured in a continuous cultivation in which the previous termtemperaturenext term was periodically increased to 42–45 °C and lowered to 37 °C again in periods of 12 h. Our investigation shows that a non-thermotolerant previous termyeastnext term strain improved its heat tolerance upon previous termencapsulationnext term, and could produce previous termethanolnext term at previous termtemperaturesnext term as high as 45 °C for a short time. The possibility of performing fermentations at higher previous termtemperaturesnext term would greatly improve the enzymatic hydrolysis in simultaneous saccharification and fermentation (SSF) processes and thereby make the bioethanol previous termproductionnext term process more economically feasible.

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