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    Levan production by Zymomonas mobilis in batch and continuous fermentation systems
    (Elsevier Sci Ltd, 2014) Silbir, Selim; Dagbagli, Seval; Yegin, Sirma; Baysal, Taner; Goksungur, Yekta
    Levan production in batch and continuous fermentation systems by Zymomonas mobilis B-14023 was investigated. The culture medium used in both of the fermentation systems contained sucrose and various organic nitrogen sources. Maximum concentration of levan was produced with yeast extract among the nitrogen sources tested. Response surface methodology was used to investigate the effects of three factors on the concentration of levan in batch cultures of Z. mobilis. Maximum levan concentration was 40.2 g/L and this concentration was reached at the optimum levels of process variables, which were 299.1 g/L initial substrate concentration, 42.3 h incubation time, and initial pH 6.0. Continuous fermentation experiments were done in packed bed bioreactor using Ca-alginate immobilized Z. mobilis cells. The highest levan concentration (31.8 +/- 0.21 g/L) was obtained at a dilution rate of 0.14 h(-1) while maximum volumetric productivity (6.556 g/(Lh)) was obtained at a dilution rate of 0.22 h(-1). Increasing the dilution rate resulted in decreased levan and increased residual sugar concentrations. (C) 2013 Elsevier Ltd. All rights reserved.
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    Optimization of beta-Galactosidase Production in Stirred Tank Bioreactor Using Kluyveromyces lactis NRRL Y-8279
    (Korean Society Food Science & Technology-Kosfost, 2009) Dagbagli, Seval; Goksungur, Yekta
    This paper investigates the production and optimization of beta-galactosidase enzyme using synthetic medium by Kluyveromyces lactis NRRL Y-8279 in stirred tank bioreactor. Response surface methodology was used to investigate the effects of fermentation parameters on P-galactosidase enzyme production. Maximum specific enzyme activity of 4,622.7 U/g was obtained at the optimum levels of process variables (aeration rate 2.21 vvm, agitation speed 173.4 rpm, initial sugar concentration 33.8 g/L, incubation time 24.0 hr). The optimum temperature and pH of the P-galactosidase enzyme produced under optimized conditions were 37 degrees C and pH 7.0, respectively. The enzyme was stable over a pH range of 6.0-7.5 and a temperature range of 25-37 degrees C. The K-m and V-max values for O-nitrophenol-beta-D-galactopyranoside (ONPG) were 1.20 mM and 1,000 mu mol/min.mg protein, respectively. The response surface methodology was found to be useful in optimizing and determining the interactions among process variables in beta-galactosidase enzyme production. Hence, this study fulfills the lack of using mathematical and statistical techniques in optimizing beta-galactosidase enzyme production in stirred tank bioreactor.
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    Optimization of beta-Galactosidase Production in Stirred Tank Bioreactor Using Kluyveromyces lactis NRRL Y-8279
    (Korean Society Food Science & Technology-Kosfost, 2009) Dagbagli, Seval; Goksungur, Yekta
    This paper investigates the production and optimization of beta-galactosidase enzyme using synthetic medium by Kluyveromyces lactis NRRL Y-8279 in stirred tank bioreactor. Response surface methodology was used to investigate the effects of fermentation parameters on P-galactosidase enzyme production. Maximum specific enzyme activity of 4,622.7 U/g was obtained at the optimum levels of process variables (aeration rate 2.21 vvm, agitation speed 173.4 rpm, initial sugar concentration 33.8 g/L, incubation time 24.0 hr). The optimum temperature and pH of the P-galactosidase enzyme produced under optimized conditions were 37 degrees C and pH 7.0, respectively. The enzyme was stable over a pH range of 6.0-7.5 and a temperature range of 25-37 degrees C. The K-m and V-max values for O-nitrophenol-beta-D-galactopyranoside (ONPG) were 1.20 mM and 1,000 mu mol/min.mg protein, respectively. The response surface methodology was found to be useful in optimizing and determining the interactions among process variables in beta-galactosidase enzyme production. Hence, this study fulfills the lack of using mathematical and statistical techniques in optimizing beta-galactosidase enzyme production in stirred tank bioreactor.
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    Optimization of beta-galactosidase production using Kluyveromyces lactis NRRL Y-8279 by response surface methodology
    (Univ Catolica De Valparaiso, 2008) Dagbagli, Seval; Goksungur, Yekta
    This paper investigates the production and optimization of beta-galactosidase enzyme using synthetic medium by Kluyveromyces lactis NRRL Y-8279 in shake flask cultures. Among the different cell disintegration methods used, the highest specific activity was obtained when the cells were permeabilized using isoamyl alcohol. Response surface methodology was used to investigate the effects of four fermentation parameters (agitation speed, pH, initial substrate concentration and incubation time) on beta-galactosidase enzyme production. Results of the statistical analysis showed that the fit of the model was good in all cases. Maximum specific enzyme activity of 4218.4 U g(-1) was obtained at the optimum levels of process variables (pH 7.35, agitation speed 179.2 rpm, initial sugar concentration 24.9 g l(-1) and incubation time 50.9 hrs). The response surface methodology was found to be useful in optimizing and determining the interactions among process variables in beta-galactosidase enzyme production.
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    Optimization of pullulan production from hydrolysed potato starch waste by response surface methodology
    (Elsevier Sci Ltd, 2011) Goksungur, Yekta; Uzunogullari, Purlen; Dagbagli, Seval
    The production of pullulan from hydrolysed potato starch waste by Aureobasidium pullulans P56 was investigated. The liquefaction of potato starch was done by Ca-alginate immobilized amyloglucosidase and pullulanase enzymes in a packed bed bioreactor. Various organic nitrogen sources were tested and none of the nitrogen sources gave pullulan concentrations as high as that obtained with yeast extract. Response surface methodology was used to investigate the effects of three factors (incubation time, initial substrate concentration and initial pH) on the concentration of pullulan in batch cultures of A. pullulans. No previous work has used statistical analysis on the optimization of process parameters in pullulan production from hydrolysed potato starch waste. Maximum pullulan concentration of 19.2 g/l was obtained at the optimum levels of process variables (incubation time 111.8 h, initial substrate concentration 79.4 g/l, initial pH 7.26). The optimization led to a 20% increase in pullulan concentration. (C) 2010 Elsevier Ltd. All rights reserved.
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    Optimization of pullulan production using Ca-alginate-immobilized Aureobasidium pullulans by response surface methodology
    (John Wiley & Sons Ltd, 2007) Uerkuet, Zuemruet; Dagbagli, Seval; Goeksungur, Yekta
    BACKGROUND: The production of pullulan from synthetic medium by Aureobasidium pullulans P56 immobilized in Ca-alginate beads was investigated using batch and repeated batch fermentation systems. RESULTS: The highest pullulan concentration (19.52 +/- 0.37 g dm(-3)) was obtained with 2.0-2.4 mm. beads prepared from 2% sodium alginate solution. Pullulan production was mainly accomplished by immobilized fungal cells since leaked cells in the fermentation medium comprised 17.4% of the total fungal population at the end of fermentation. The pullulan proportion was 84.5% of the total polysaccharide in the fermentation medium. Response surface methodology was used to investigate the effects of three fermentation parameters (initial pH, agitation speed and incubation time) on the concentration of pullulan. Results of the statistical analysis showed that the fit of the model was good in all cases. The maximum pullulan concentration of 21.07 +/- 0.48 g dm(-3) was obtained at the optimum concentrations of process variables (pH 7.31, agitation speed 191.5 rpm, incubation time 101.2 h). The gel beads produced pullulan under the optimized conditions for six consecutive batch fermentations without marked activity loss and deformation. CONCLUSION: The results of this study suggest that the immobilization of A. pullulans cells in Ca-alginate gel beads is suitable for batch and repeated batch production of pullulan. (C) 2007 Society of Chemical Industry.