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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Chromatography B: Biomedical Sciences and Applications 584 (1992), S. 129-133 
    ISSN: 0378-4347
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 57 (1998), S. 95-108 
    ISSN: 0006-3592
    Keywords: Xanthan fermentation ; impeller type ; power consumption ; mixing ; oxygen transfer ; Xanthan productivity ; product quality ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The rheological complexity of Xanthan fermentations presents an interesting problem from a mixing viewpoint, because the phenomena of poor bulk blending and low oxygen mass transfer rates inherent in highly viscous fermentations (and their consequences) can be systematically investigated, even at the pilot plant scale. This study in a 150 L fermentor compares the physical and biological performance of four pairs of impellers: a standard Rushton turbine, a large diameter Rushton turbine, a Prochem Maxflo T, and a Scaba 6SRGT. Accurate in-fermentor power measurements, essential for the comparison of impellers in relation to operating costs are also reported. It is demonstrated that the agitator performance in Xanthan fermentations is very specific and the choice of which impeller to use in bioreactors to obtain enhanced performance is dependant on the applied criterion. None of the criterion favored the use of the standard Rushton turbine, therefore suggesting that there are strong grounds for retrofitting these impellers with either large diameter impellers of similar design or with novel agitators. In addition, fluid dynamic modeling of cavern formation has clearly highlighted the importance of a well mixed and oxygenated region for providing the capacity for high microbial oxygen uptake rates which govern Xanthan productivity and quality. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 95-108, 1998.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0178-515X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  Three impeller-sparger configurations were used to evaluate the effect of different hydrodynamic conditions over fungal growth in rheologically complex cultures of Trichoderma harzianum using castor oil as sole carbon source. Three spargers (ring, sintered and 5-orifice) in combination with a turbine impeller system “TIS” (two Rushton turbines) or a hybrid impeller system “HIS” (Rushton turbine and a marine propeller as lower and upper impellers) were used. Their performance was assessed in terms of the response towards disturbance (PID oxygen control settings) and oxygen mass transfer (k L a). To avoid oxygen limitations, all cultures were controlled at 10% DOT by gas blending. Top to bottom mixing, and hence bulk blending, was improved when the – axial flow – HIS was used, ensuring phase interaction and substrate (oil) circulation. The 5-orifice sparger in combination with the TIS configuration yielded the longest lag phase and lowest k L a due to poor bulk blending and to the low gas–liquid interfacial area developed. The highest k L a was achieved with the sintered sparger-HIS probably due to considerable interfacial bubble area enhancement. However, growth limitation occurred as consequence of poor substrate availability as a stable air–oil emulsion was formed at the top of the tank. The best compromise between bulk blending (phase interaction), oxygen transfer (k L a) and fungal growth (growth rate) was achieved with the ring sparger-HIS configuration.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Biosynthesis of 6-pentyl-α-pyrone byTrichoderma harzianum in two different media was evaluated. Best yields were found in nitrogen deficient medium (C/N=60). Limited growth seems to favour the production of this lactone. When fungal cells, precultured in low nitrogen medium, were incubated on methyl ricinoleate (10 g/l, C/N=60) an increase in 6-pentyl-α-pyrone production was observed in comparison with the media containing methyl oleate or methyl linoleate.
    Type of Medium: Electronic Resource
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