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  • Articles  (34)
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  • yeast  (34)
  • 1990-1994  (34)
  • Process Engineering, Biotechnology, Nutrition Technology  (34)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    World journal of microbiology and biotechnology 10 (1994), S. 410-413 
    ISSN: 1573-0972
    Keywords: Enterobacteriaceae ; fermentation ; lactic acid bacteria ; maize ; mawè ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Lactic acid bacteria increased from 3.2 × 106 and 1.6 × 107 c.f.u./g (wet wt) to 2 × 109 and 1.6 × 109 c.f.u./g after 12 to 24 h of fermentation of home-produced mawè (a dough produced from dehulled maize) and commercial mawè, respectively. In commercial mawè, the yeast count increased from 1.3 × 105 to 2.5 × 107 c.f.u./g after 48 h of fermentation before decreasing, whereas in the home-produced mawè it increased from 2.5 × 104 to 3.2 × 107 c.f.u./g after 72 h of fermentation; the dominant yeasts were mainly Candida krusei, although C. kefyr, C. glabrata and Saccharomyces cerevisiae were also present. Enterobacteriaceae counts increased slightly during the initial stage ofthe fermentation, but decreased below the detection level after 24 to 48 h. Enterobacter cloacae was mostly found in commercial mawè and Escherichia coli mostly in homeproduced mawè.
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  • 2
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    Springer
    World journal of microbiology and biotechnology 10 (1994), S. 354-355 
    ISSN: 1573-0972
    Keywords: Inulinase ; Kluyveromyces marxianus ; sauerkraut brine ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Kluyveromyces marxianus NRRL Y-1196 produced the highest inulinase activity (38 U/mg protein) of six yeasts examined after 24 h growth in sauerkraut brine in shaking flasks at 30°C with 0.3% inulin as an enzyme inducer. The enzyme was recovered by acetone fractionation, with a yield of 81%. It had maximum activity at pH 4.4 and 55°C with K m values for inulin and sucrose of 3.92 mm and 11.9 mm, respectively. The yeast raised the pH from 3.4 to above 7.0, using all the lactic acid in the brine. Growth of K. marxianus in sauerkraut brine with a small amount of inulin may usefully decrease the BOD and concomitantly produce inulinase.
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  • 3
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    Springer
    World journal of microbiology and biotechnology 10 (1994), S. 385-387 
    ISSN: 1573-0972
    Keywords: Diacetyl reductase ; enzyme ; Kluyveromyces marxianus ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Kluyveromyces marxianus had a higher specific activity of diacetyl reductase (EC 1.1.1.5) than all other organisms previously reported. The enzyme was NADH-dependent and irreversibly catalysed the conversion of diacetyl to acetoin with an optimum pH of 7.0. It was stable at 40°C but lost 50% of its activity at 50°C in 30 min. The K m and V max values for diacetyl were 1.8 mm and 0.053 mm/min, respectively.
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  • 4
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    Springer
    World journal of microbiology and biotechnology 10 (1994), S. 488-490 
    ISSN: 1573-0972
    Keywords: Bacteria ; microbial load ; moulds ; non-alcoholic drinks ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract When microbiological analyses were conducted on 90 samples of soft drinks representing 30 different products commercially available in Nigeria, contaminants were detected in 50% of them. The isolates were mainly saprophytic and non-pathogenic: Bacillus spp. (35%), Lactobacillus spp. (26%), Pediococcus spp. (6%), Staphylococcus epidermidis (6%) and Micrococcus spp. (3%) accounted for the bacterial isolates while Aspergillus niger (6%) and Saccharomyces spp. (16%) accounted for the fungal isolates.
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  • 5
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    Springer
    World journal of microbiology and biotechnology 10 (1994), S. 505-509 
    ISSN: 1573-0972
    Keywords: Acetic acid ; chemostat ; Geotrichum ingens ; growth ; inhibition ; kinetics ; monocarboxylic acids ; propionic acid ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Growth of Geotrichum ingens in batch cultures was completely inhibited by 47 g acetic acid/l or 33 g propionic acid/I. With mixtures of acetic and propionic acids, however, growth only ceased at 55 g/l. Acetic acid inhibited growth linearly, whereas propionic acid inhibited growth non-linearly. In continuous culture, two steady states at each dilution rate were observed at high dilution rates for acetic acid and propionic acid. The highest yield coefficient (0.69 g cells/g substrate) was achieved with propionic acid as substrate. On both substrates and their mixtures, the protein content of the biomass increased when the dilution rate was increased.
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  • 6
    Electronic Resource
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 165-170 
    ISSN: 0006-3592
    Keywords: visualization chamber ; osmotic pressure ; yeast ; image analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A visualization chamber has been developed to analyze potential correlations between osmotic step increase on yeasts and the resultant cell volume decreases. Image analysis was used to characterize the step increases in the center of the chamber and to measure the changes in the cell volume. Step increases of different intensities have been performed on the yeast Saccharomyces cerevisiae. This device has allowed the kinetics of the volumetric evolution of the cells to be observed. The water exit flow rate from the cell was found to occur in the first 10 s following the hypertonic step change. Comparison of the time constants of the chamber and of the cell volume variations allowed to conclude that the time constant of the water transfer across the membrane was short (about 1 s). © 1994 John Wiley & Sons, Inc.
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  • 7
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 155-158 
    ISSN: 0006-3592
    Keywords: Zymomonas ; yeast ; ethanol ; inhibition ; adaptation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In high cell density batch fermentations, Zymomonas mobilis produced 91 g L-1 ethanol in 90 min but culture viability fell significantly. Similar viability losses in rapid fermentations by yeast have recently been shown to be attributable in part to the high rate of change of the extracellular ethanol concentration. However, in simulated rapid fermentations in which ethanol was pumped continuously to low cell density Z. mobilis suspensions, increases in the rate of change of ethanol concentration in the range 21-83 g L-1 h-1 did not lead to accelerated viability losses. The lag phase of Zymomonas cultures exposed to a 30-g L-1 step change in ethanol concentration was much shorter than that of Saccharomyces cerevisiae, providing evidence that the comparative insensitivity of Zymomonas to high rates of change of ethanol concentration is due to its ability to adapt to changes in ethanol concentration more rapidly than yeast. © 1994 John Wiley & Sons, Inc.
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  • 8
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 888-894 
    ISSN: 0006-3592
    Keywords: Rhodotorula glutinis ; Lactobacillus helveticus ; yeast ; whey ; carotenoids ; carotenogenesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The growth and carotenoid biosynthesis of the yeast Rhodotorula glutinis was studied by cocultivation with Lactobacillus helveticus in cheese ultrafiltrate containing 3.9% and 7.1% lactose. By growing this mixed culture in a 15-L fermentor MBR AG (Switzerland) at an air flow rate of 0.5 L/L min and agitation at 220 rpm for 6 days, a total yield of carotenoids of 268 μg/g dry cells wasobtained. Carotenoids were formed almost parallel with the cell growth, anda maximum production was reached at an early stationary phase. A high-performance liquid chromatographic system (HPLC) permitting simultaneous determination of major carotenoid pigments was used. The three main pigments (torularhodin, β-carotene, and torulene) were formed in Rhodotorula glutinis, and reached a maximum concentration as follows: 182.0, 43.9, 23.0 μg,g dry cells. © 1994 John Wiley & Sons, Inc.
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  • 9
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 297-302 
    ISSN: 0006-3592
    Keywords: cell walls ; metal binding ; polymers ; yeast ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Isolated cell walls of the yeast Saccharomyces cerevisiae were treated by either chemical (alkali and acid) or enzymatic (protease, mannanase or β-glucuronidase) processes to yield partially purified products. These products were partially characterized by infrared analysis. They were subsequently reacted with heavy metal cation solutions and the quantity of metal accumulated by the cell wall material determined. The Cu2+ ion (0.24, 0.36, 1.12, and 0.60 μmol/mg) was accumulated to a greater extent than either Co2+ (0.13, 0.32, 0.43, and 0.32 μmol/mg) or Cd2+ (0.17, 0.34, 0.39, and 0.32 μmol/mg) by yeast cell walls, glucan, mannan, and chitin, respectively The isolated components each accumulated greater quantities of the cations than the intact cell wall. Removal of the protein component of the yeast cell walls by Pronase caused a 29.5% decrease in metal accumulation by yeast cell walls per mass, indicating the protein is a heavy metal accumulating component. The data indicate that the outer mannan-protein layer of the yeast cell wall is more important than the inner glucan-chitin layer in heavy metal action accumulation. © 1994 John Wiley & Sons, Inc.
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  • 10
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 337-341 
    ISSN: 0006-3592
    Keywords: yeast ; on-line ; capacitance ; viable biomass ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A commercially available biomass monitor has been employed in a number of applications. For capacitance monitors, a relationship between capacitance measurement and cell counts or colony forming units has been reported in the literature. However, for use as an online instrument, a more practical correlation with the biomass concentration is needed. In this study, we followed the batch growth of brewer's yeast and a correlation with viable biomass concentration (g DW/L) was demonstrated. This correlation was utilized with the capacitance biomass monitor in a control loop to maintain setpoint biomass levels in a cyclic reactor under perturbations. Not only did the system demonstrate the capability of the biomass monitor to control biomass in such a system, but it also confirmed the correlation reported in our earlier work. © 1994 John Wiley & Sons, Inc.
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  • 11
    ISSN: 1573-0972
    Keywords: Ethanol ; fermentation ; modelling ; molasses ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Batch fermentations of sugar-cane blackstrap molasses to ethanol, using pressed yeast as inoculum, demonstrated an exponential relationship between the time necessary to complete the fermentation and the initial concentrations of sugar and yeast cells. The parameters of the derived exponential equations depended on the experimental conditions.
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  • 12
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    World journal of microbiology and biotechnology 9 (1993), S. 153-155 
    ISSN: 1573-0972
    Keywords: Catabolite repression ; dextranase ; mutant ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A mutant strain of Lipomyces kononenkoae 2896-3 synthesizing dextranase but resistant to catabolite repression was obtained using N-nitroso-N-methylurea treatment. Enzyme biosynthesis in media with dextran and other carbon sources was then characterized. The capacity of the mutant to produce dextranase when grown on hydrolysed corn starch is demonstrated.
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  • 13
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    World journal of microbiology and biotechnology 9 (1993), S. 338-341 
    ISSN: 1573-0972
    Keywords: Absence of nutritional supplements ; ethanol ; starch ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Static fermentation of starch to ethanol by a co-culture of Saccharomycopsis fibuligera and Saccharomyces cerevisiae without addition of nutritional supplements was investigated with respect to initial starch concentration, pH of the media and initial dry weight ratio of Sps. fibuligera to Sacc. cerevisiae biomass (I R).Optimal conditions for ethanol production were: starch from 20 to 30 g/l; initial pH values from 5.8 to 6.0; and I R values of 2.0 or 3.0. The highest attained ethanol concentration, 13.7 g/l, represented 88% of the theoretical yield.
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  • 14
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    World journal of microbiology and biotechnology 9 (1993), S. 662-663 
    ISSN: 1573-0972
    Keywords: Biosynthesis ; invertase ; molasses ; Saccharomyces cerevisiae ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Biosynthesis of invertase by Saccharomyces cerevisiae 01K32 was inversely proportional to the concentration of sugarcane blackstrap molasses included in the medium. In a fermenter, an intracellular invertase activity of 440 U/g dry cells was obtained.
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  • 15
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    World journal of microbiology and biotechnology 9 (1993), S. 308-312 
    ISSN: 1573-0972
    Keywords: Fermentation variation ; growth ; inoculation ; Saccharomyces ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Substantial losses occur in the fermentation industry each year due to variability in yields and productivity. As the first stage in the process, inoculum consistency, in terms of size and quality, is clearly important. Yet, despite this, most inoculum development processes involve at least one highly variable transfer step, usually by wire loop, from a culture grown on a solid (agar) substrate. It is likely, then, that at least some of the variability in the production process can be attributed to a poorly controlled initial inoculation process. Experiments to determine the inherent variability of the conventional loop transfer technique showed a 12-fold variation in inoculum size. Although this can be improved by adopting a more rigid protocol, consistency is still poor. A simple alternative system, based on liquid transfers, leads to substantial improvements in the reproducibility of inoculum size and quality.
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  • 16
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    World journal of microbiology and biotechnology 9 (1993), S. 357-360 
    ISSN: 1573-0972
    Keywords: Candida utilis ; inhibition ; kinetics ; regulation ; sugar ; transport ; xylose ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Low-affinity (K m=67.6±3.2 mM) and high-affinity (K m=1.9±1.2 mM) D-xylose transport occur in Candida utilis grown, respectively, on D-glucose or D-xylose. Starvation of glucose-grown cells decreases the K m value (10.5±2.6 mm). The high-affinity system appearing during starvation required protein synthesis and it was inactivated when cells were exposed to glucose, by a process independent of protein synthesis. High-affinity transport was accompanied by transient alkalinization of yeast suspensions, indicating that it is a proton symport, whereas low-affinity transport was not. Both systems, however, were inhibited by metabolic inhibitors and by replacing H2O in the transport assay with D2O, indicating that both may be proton symports. Glucose and acetic acid also inhibited both high-and low-affinity xylose transport.
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  • 17
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    World journal of microbiology and biotechnology 9 (1993), S. 514-520 
    ISSN: 1573-0972
    Keywords: Astaxanthin ; mannitol ; mutants ; NTG ; Phaffia rhodozyma ; succinate ; valine ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Mutagenesis of Phaffia rhodozyma with NTG yielded a mutant with an astaxanthin content of 1688 μg (g dry biomass)-1, a cell yield coefficient of 0.47 on glucose and a maximum specific growth rate of 0.12 h-1. Re-mutation of the mutant decreased the cell yield and maximum specific growth rate but increased the astaxanthin content. The use of mannitol or succinate as carbon sources enhanced pigmentation, yielding astaxanthin contents of 1973 μg g-1 and 1926 μg g-1, respectively. The use of valine as sole nitrogen source also increased astaxanthin production, but severely decreased the maximum specific growth rate and cell yield coefficient. The optimum pH for growth of P. rhodozyma was between pH 4.5 and 5.5, whereas the astaxanthin content remained constant above pH 3.
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  • 18
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    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 42 (1993), S. 295-302 
    ISSN: 0006-3592
    Keywords: intracellular pH ; bioreactors ; cultivation ; yeast ; 9-aminoacridine ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Intracellular pH (pHi) was measured on-line in a bioreactor using a fluorescent pHi indicator, 9-aminoacridine, and controlled fed-batch cultivations of yeast cells based on pHi (FB-pHi) were performed. In FB-pHi cultivations, automated glucose additions were made to the culture in response to culture pHi. The average ethanol (an-aerobic product) yield was significantly lower [0.12 g g-1 glucose in fed-batch pHi cultivations with 100 ppm glucose additions (FB-pHi-100 cultivation) vs. 0.48 g g-1 glucose in batch] and cell yield was higher (0.54 g g-1 glucose in FB-pHi-100 cultivation vs. 0.3 g g-1 glucose in batch) compared to batch cultivation. An expression has been derived to calculate changes in pHi from measured fluorescence values when the cell concentration increases during growth. Cultivations based on pHi, performed with different magnitudes of glucose addition (100, 50, and 10 ppm additions), showed that lower magnitudes of glucose addition resulted in lower ethanol yields while cell yield remained unaffected. The ratio of specific oxygen uptake rate to specific glucose uptake rate (OUR/GUR) increased with decreased in magnitude of glucose additions in FB-pHi cultivations, suggesting that the culture aerobic state was higher when the magnitude of glucose addition was lower. The average cell productivity in FB-pHi cultivations was 29% higher than in batch cultivation. Cells were also cultivated at high OUR conditions, and the results are compared with other cultivations. © 1993 John Wiley & Sons, Inc.
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  • 19
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    Biotechnology and Bioengineering 42 (1993), S. 351-356 
    ISSN: 0006-3592
    Keywords: microencapsulation ; selection ; secretion ; yeast ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have developed a microencapsulation selection method which allows the rapid and quantitative screening of 〉106 yeast cells for enhanced secretion of Aspergillus awamori glucoamylase. The method provides a 400-fold single-pass enrichment for high-secreting mutants, and can be straightforwardly adapted for application to growth-based selection schemes with other microorganisms and enzymes. © 1993 John Wiley & Sons, Inc.
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  • 20
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    Biotechnology and Bioengineering 42 (1993), S. 1151-1156 
    ISSN: 0006-3592
    Keywords: fatty acid synthesis ; yeast ; Rhodotorula glutinis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In nitrogen-limited media, growth and fatty acid formation by the oleaginous yeast Rhodotorula glutinis, i.e., yield and fatty acid cell content, have been characterized regarding carbon and nitrogen availabilities. It was shown that the formation of fatty acid free biomass was limited by nitrogen availability, whereas the fatty acid production was directly dependent on the consumed C/N ratio. According to these observations, the fraction of substrate consumed for fatty acid synthesis was estimated by using a simple method based on the actual yields, i.e., the mass of carbon source strictly converted into fatty acids and fatty acid free biomass. From these results, relationships were established allowing to predict in a simple and performing manner the maximal attainable fatty acid cell content and yield from the available carbon and nitrogen. These relationships were validated by using experimental data obtained by various authors with different yeast strains, and the proposed method was compared to the energetic and mass balance method previously described. © 1993 John Wiley & Sons, Inc.
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  • 21
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    Biotechnology and Bioengineering 42 (1993), S. 43-49 
    ISSN: 0006-3592
    Keywords: calcium alginate reactor ; NADH regeneration ; Saccharomyces cerevisiae ; yeast ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Saccharomyces cerevisiae cells immobilized in a calcium alginate fiber reactor were used as a source of alcohol dehydrogenase for the NAD+-to-NADH reaction. The reaction was catalyzed by enzyme in cells on the surface of the fiber. Internal diffusional effects were present. The enzyme cell concentration was optimized by harvesting cells finally grown under anaerobic conditions. The results were expressed as an apparent reaction rate constant that was independent of NAD+ and excess ethanol concentration, was slightly affected by flow rate above a minimum value, and increased with immobilized cell concentration in the fiber. The reaction was complete after 6 to 7 h under optimal conditions of 36°C and 9.5 pH. The latter was 0.5 pH units above the free enzyme optimum, indicating that microenvironmental effects were in evidence. © 1993 John Wiley & Sons, Inc.
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  • 22
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    Biotechnology and Bioengineering 42 (1993), S. 836-842 
    ISSN: 0006-3592
    Keywords: acid phosphatase ; yeast ; enzyme induction ; electrochemical modulation ; PHO gene ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel modulating method of the expression of Saccharomyces PHO 5 gene, responsible for acid phosphatase (APase), is proposed. The method is based on electrochemical modulation of an effector (inorganic phosphate) concentration, as the gene expression is initiated below a threshold concentration of phosphate and is terminated above the threshold value. By positioning the yeast in the close neighborhood of a conducting polymer, the authors show the effectiveness of the electrochemical approach toward PHO 5 induction. Based on the approach, phosphate concentration is easily modulated at the boundary concentration by taking advantage of anion doping-undoping at a conducting polymer and the resulting anion localization-delocalization in the polymer, as the local enrichment of phosphate in the polymer results in the lowering of phosphate in the vicinity of polypyrrole. External phosphate concentration is thus electrochemically modulated when the conducting polymer is positioned in the close neighborhood of the yeast cells; thereby the PHO gene is induced. Here an electrochemical approach for the APase expression as a strategy of selective induction of specific genetic information is described. © 1993 John Wiley & Sons, Inc.
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  • 23
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    Biotechnology and Bioengineering 42 (1993), S. 24-29 
    ISSN: 0006-3592
    Keywords: acetaldehyde ; intracellular accumulation ; inhibition ; transport ; yeast ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The rate of acetaldehyde efflux from yeast cells and its intracellular concentration were studied in the light of recent suggestions that acetaldehyde inhibition may be an important factor in yeast ethanol fermentations. When the medium surrounding cells containing ethanol and acetaldehyde was suddenly diluted, the rate of efflux of acetaldehyde was slow relative to the rate of ethanol efflux, suggesting that acetaldehyde, unlike ethanol, may accumulate intracellularly. Intracellular acetaldehyde concentrations were measured during high cell density fermentations, using direct injection gas chromatography to avoid the need to concentrate or disrupt the cells. Intracellular acetaldehyde concentrations substantially exceeded the extracellular concentrations throughout fermentation and were generally much higher than the acetaldehyde concentrations normally recorded in the culture broth in ethanol fermentations. The technique used was sensitive to the time taken to cool and freeze the samples. Measured intracellular acetaldehyde concentrations fell rapidly as the time taken to freeze the suspensions was extended beyond 2 s. The results add weight to recent claims that acetaldehyde toxicity is responsible for some of the effects previously ascribed to ethanol in alcohol fermentations, especially Zymomonas fermentations. Further work is required to confirm the importance of acetaldehyde toxicity under other culture conditions. © 1993 John Wiley & Sons, Inc.
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  • 24
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    Biotechnology and Bioengineering 41 (1993), S. 118-128 
    ISSN: 0006-3592
    Keywords: intracellular pH ; 9-aminoacridine ; bioreactor ; on-line measurement ; yeast ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A method has been developed to continuously measure the intracellular pH (pHi) of cells cultivated in a bioreactor in an on-line fashion over extend time periods. The methods is attractive in its simplicity and involves the use of a fluorescent pHi indicator 9-aminoacridine (9A A) which is a week base. An expression has been derived to calculate changes in pHi from measured 9AA-fluorescence changes. The indicator 9AA was found t be nontoxic to yeast cells at concentrations used to measure pHi (7 μM). The fluorescence of nicotinamide adenine dinucleotide (NADH) molecules did not interfere significantly with the measurement of 9AA-fluorescence. The pHi change in yeast cell following the addition of a proton ionophore carbonyl cyanide m-chlorophenyl hydrazone (CCCP) measured by 9AA compared favorably with that measured by the well-established pHi, indicator (which is however unsuitable for on-line applications in a bioreactor) bis-carboxyethyl carboxy fluorescein (BCECF). The pHi of yeast under substrate starved conditions was 6.4 units. The responses of pHi of yeast cells to induced metabolic transitions were studied. Under aerobic condition, pHi increased by 0.12 unit following a 100-ppm glucose pulse addition and by 0.25 unit following a 300-ppm ethanol pulse addition. Under anaerobic condition, pHi increased by 0.1 unit following a 500-ppm glucose pulse addition. Comparison of pHi with other indicators of cellular metabolic state suggests that pHi is a cellular metabolic state indicator. © 1993 John Wiley & Sons, Inc.
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  • 25
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    Biotechnology and Bioengineering 41 (1993), S. 647-653 
    ISSN: 0006-3592
    Keywords: yeast ; continuous-flow 31P NMR ; intracellular pH ; immobilization ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Phosphorus-31 nuclear magnetic resonance (31P NMR) was used to compare the anaerobic metabolism of glucose by suspended and gel-entrapped Saccharomyces bayanus cells. The fermentation of glucose was carried out in a reaction system with continuous circulation through the NMR sample tube. The intracellular pH and the levels of some phosphorylated compounds were the levels of some phosphorylated compounds were noninvasively monitored by 31P NMR while glucose, fermentation products, and biomass were determined by analytic techniques comparisons showed that no significant differences are observed in the relative concentrations in the spectra, but distinct profiles for the variation of both intracellular and extracellular pH are found. The internal pH of immobilized cells is maintained at a constant value throughout the fermentation as opposed to freely suspended cells for which a steady decrease in the internal pH occurs. A faster and stronger acidification is also observed in the external medium of the assays with suspended cells. Furthermore, higher yields for ethanol and biomass production and lower yields of fermentation by-products are obtained with immobilized cells. It is concluded that the higher intracellular pH achieved in the presence of the gel matrix had a regulatory effect on the metabolism which favored the ethanol production pathway. © 1993 John Wiley & Sons, Inc.
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  • 26
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    World journal of microbiology and biotechnology 8 (1992), S. 416-422 
    ISSN: 1573-0972
    Keywords: Amylase ; Candida utilis ; grain sorghum ; Lipomyces kononenkoae ; protein ; Schwanniomyces occidentalis ; starch ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Cultivation of aSchwanniomyces occidentalis derepressed mutant in a 10% (w/v) gelatinized grain sorghum slurry increased the crude protein content of the biomass from an initial value of 12% to 41% (dry) within 20 h, with no detectable residual starch. Co-cultivation ofCandida utilis with theS. occidentalis mutant improved the final crude protein content to 47% within 18 h, whereas a co-culture ofC. utilis with aLipomyces kononenkoae mutant resulted in a cultivation time of 50 h with a significantly lower protein content and a low final α-amylase activity. In a 15% (w/v) grain sorghum slurry aC. utilis/S. occidentalis co-culture increased the protein content to about 44% within 30 h. Yeast cultivation increased the lysine and threonine content of the final biomass considerably.
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  • 27
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    World journal of microbiology and biotechnology 8 (1992), S. 14-20 
    ISSN: 1573-0972
    Keywords: Candida apicola ; protoplast ; vesicles ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract The optimal conditions for protoplast formation ofCandida apicola were by using an enzyme fromArthrobacter sp. in combination with 2-mercaptoethanol. The kinetic data support the two-layered structure model of cell wall for this yeast but the structure of the cell wall depended on the age of cells and culture conditions. To regenerate the protoplasts, the type of osmotic stabilizer was important: sorbitol gave 16 to 30% regeneration. Electron microscopy revealed the presence of vesicles in the sections of protoplasts and whole cells ofCandida apicola grown in production medium and producing glycolipids. In sections of whole cells, vesicle-like structures are located in the periplasmic space and in protoplasts they can either be attached to, or released from, the cell surface. These vesicles are thought to be involved in the transport of the surface-active glycolipids and in the protection of the cell against denaturing effects.
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  • 28
    ISSN: 1573-0972
    Keywords: Fatty acids ; lipid ; Rhodotorula ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Microbial lipids produced byRhodotorula glutinis grown in continuous culture with molasses under nitrogen-limiting conditions were evaluated and the effects of growth rate on fatty acid composition were studied. As the growth rate decreased, cell biomass, lipid content and lipid yield gradually increased. The maximum lipid content recorded was 39% (w/w) of dry cell biomass at a dilution rate of 0.04 h−1. The growth rate also affected fatty acid composition: oleic acid decreased with decreasing growth rate while stearic acid increased.
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  • 29
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    World journal of microbiology and biotechnology 8 (1992), S. 382-384 
    ISSN: 1573-0972
    Keywords: Lipid ; oleaginous ; pH effect ; Rhodotorula glutinis ; yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Maximum lipid production (66% w/w dry wt) inRhodotorula glutinis IIP-30 utilizing glucose in a fed-batch fermentation under N-limiting conditions at 30°C, was at pH 4. At pH 3, 5 and 6, the lipid contents were 12%, 48% and 44%, respectively. There was only a small change in the fatty acid profile over the pH range examined, although the ergosterol content decreased by a third as the pH increased.
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  • 30
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    Biotechnology and Bioengineering 40 (1992), S. 475-482 
    ISSN: 0006-3592
    Keywords: yeast ; diffusion ; mass transfer ; sucrose ; floc structure ; fractal ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The sucrose hydrolysis activity of dense spherical yeast flocs, cultivated on a sucrose medium in a continuous reactor with internal settler, is nearly proportional to the particle surface. From computer simulation, in good agreement with experimental determinations, the calculated sucrose penetration depth is in the range 0.2-0.3 mm, a dimension smaller than the usual diameter of strongly flocculating yeast particles. From specific gravity determinations, the flocs can be considered as homogeneous and cannot exhibit a fractal structure, reported in the literature for a number of microbial aggregates. However, the analysis of the sucrose hydrolysis rates reveals that the cell density may be lower in the outer layer of the flocs. © 1992 John Wiley & Sons, Inc.
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  • 31
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    Biotechnology and Bioengineering 40 (1992), S. 835-843 
    ISSN: 0006-3592
    Keywords: yeast ; aggregation ; separation ; lectin ; concanavalin A ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Specific aggregation and separation of microorganisms was investigated using yeasts and concanavalin A as a model system. Cells of Saccharomyces cerevisiae were specifically aggregated and so separated from those of Schizosaccharomyces pombe. Optimum aggregation with over 99% of cells aggregated was achieved by adjustment to pH value and applied agitation. Dimeric lectin structure caused a far higher degree of aggregation than did tetrameric. Degree of aggregation was also strongly influenced by the ratio of lectin/cell concentrations, optimum aggregation occurring in the middle range of ratios. A high ratio of lectin to cells inhibited aggregation, occupation of most of the available receptors preventing intercellular bonding by divalent lectins. Detachment and reuse of concanavalin A was demonstrated using switching from moderate to low pH value. Potential uses for species-specific-separation of microorganisms are discussed. © 1992 John Wiley & Sons, Inc.
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  • 32
    ISSN: 0006-3592
    Keywords: bioreactor ; tower loop bioreactor ; yeast ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The local properties of the dispersed gas phase (gasholdup, bubble diamater, and bubble velocity) were measured and evaluated at different positions in the riser and downcomer of a pilot plant reactor and, for comparison, in a laboratory reactor. These were described in Parts I and II of this series of articles during yeast cultivation and with model media. In the riser of the pilot plant reactor, the local gas holdup and bubble velocities varied only slightly in axial direction. The gas holdup increased considerably, while the bubble velocity increased only slightly with aeration rate. The bubble size diminished with increasing distance from the aerator in the riser, since the primary bubble size was larger than the equilibrium bubble size. In the downcomer, the mean bubble size was smaller than in the riser. The mean bubble size varied only slightly, the bubble velocity was accelerated, and the gas holdup decreased from top to bottom in the downcomer. In pilot plant at constant aeration rate, the properties of the dispersed phase were nearly constant during the batch cultivation, i.e., they depended only slightly on the cell concentration. In the laboratory reactor, the mean bubble sizes were much larger than in the pilot plant reactor. In the laboratory reactor, the bubble velocities in the riser and downcomer increased, and the mean gas holdup and bubble diameter in the downcomer remained constant as the aeration rate was increased.
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  • 33
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    Biotechnology and Bioengineering 37 (1991), S. 869-875 
    ISSN: 0006-3592
    Keywords: scu-PA ; pro-urokinase ; yeast ; respiratory quotient ; fermentation ; Saccharomyces cerevisiae ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Secretion of a nonglycosylated form of human pro-urokinase, also known as single-chain urinary plasminogen activator (scu-PA), from Saccharomyces cerevisiae is described. A “supersecreting” yeast strain harboring multiple copies of integrated plasmids was grown batchwise and at constant respiratory quotient (RQ) in 20-L fermenters. Because the promoters used to drive expression of the pro-urokinase genes are not tightly regulated, secretion into the culture supernatant was growth associated. Although the final cell density achieved in the perturbed-batch fermentation (45 g dry wt/L) was less than that observed in the RQ-controlled culture (77 g dry wt/L), the scu-PA titer in the perturbed-batch fermentation (1863 IU/mL) was nearly twice that attained at constant RQ (1108 IU/mL). The effects on cell growth and scu-PA titer of other process variables (pH, temperature, phosphate concentration, and medium composition) are also discussed.
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  • 34
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    Biotechnology and Bioengineering 38 (1991), S. 1331-1336 
    ISSN: 0006-3592
    Keywords: plasmid ; yeast ; detection ; sensor ; image ; analysis ; 5-fluoro-orotic acid ; determination ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel imaging sensor system for the determination of plasmid carrying yeast cells was developed. The sensor system consisted of an Silicon Intensifier Target (SIT) video camera, a fluorescent microscope, and a personal computer system equipped with an image memory board. This system was based on the fact that the membrane integrity of only plasmid-carrying cells is lost following cell growth in 5-fluoro-orotic acid (5-FOA) containing medium, and consequently these target cell can be stained with fluorescent probes and detected. In this study, plasmid-carrying cells were detected and their fraction determined in a mixture of both plasmid-carring and plasmid-free cells. A good correlation was observed between the values determined by this sensor system and the conventional method in the 30%-80% range, and one assay was possible within 4 h. This sensor system could be used for the monitoring of plasmid-carrying fraction in recombinant yeast cells during cultivation.
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