Optimization of pullulan production from synthetic medium by Aureobasidium pullulans in a stirred tank reactor by response surface methodology

The production of pullulan from synthetic medium by Aureobasidium pullulans P56 in a stirred tank fermenter was investigated. The kinetics of polysaccharide, pullulan and biomass production was determined. Response surface methodology was used to investigate the effects of three factors (initial sugar concentration, aeration rate and agitation speed) on the concentration of pullulan in batch cultures of A pullulans. In the experiments, the range of values used for the three variables described were; 30–70 g dm^?3 initial sugar concentration, 200–600 rpm agitation speed and 1.0–3.0 vvm aeration rate. No previous work has used statistical analysis in determining the interactions among these variables in pullulan production. Results of the statistical analysis showed that the fit of the model was good in all cases. Aeration rate, agitation speed and sugar concentration had a strong linear effect on pullulan concentration. Moreover, pullulan concentration was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions with the exception that the interaction between agitation speed and aeration rate was insignificant (P > 0.05). Maximum pullulan concentration of 17.2 g dm^?3 was obtained at the optimum levels of process variables (initial sugar concentration 51.4 g dm^?3, aeration rate 2.36 vvm, agitation speed 345.3 rpm). These values were obtained by fitting of the experimental data to the model equation. Scanning electron microscope (SEM) photographs of polysaccharide particles containing different concentrations of pullulan were also taken to observe the morphological differences of the samples. Copyright © 2005 Society of Chemical Industry     

Comparison of lipase production by Geotrichum candidum in stirring and airlift fermenters

The production of lipase by Geotrichum candidum in both, stirred tank and airlift bioreactors were compared. G candidum an imperfect filamentous fungus, grows well in liquid medium, and produces a lipase with specific affinity for long‐chain fatty acids with cis‐9 double bonds but, lipase production is generally not efficient because the optimum medium composition and fermentation conditions are not known. Response surface methodology was used to optimize the agitation speed (100–500 rpm) and aeration (0.2–1.8 vvm) for production of lipase by G candidum in a bench‐scale stirred fermenter. A Central Composite Rotatable Design (CCRD) was used to optimize lipase activity and productivity. Lipase production in an airlift fermenter was also studied with aeration ranging from 1 to 3 vvm. A previously optimized culture medium containing 3.58% of peptone, 0.64% of soy oil and an initial pH of 7.0, was used in the experiments, incubating at 30°C. In the stirred reactor the optimum conditions of agitation and aeration for lipase production and productivity were 300 rpm and 1 vvm, leading to an activity of 20 U cm^?3 in 54 h of fermentation and 0.3900 (U cm^?3 h^?1) of productivity. The best aeration condition in the airlift fermenter was 2.5 vvm, which yielded similar lipase activity after 30 h of fermentation, resulting in a productivity of 0.6423 (U cm^?3 h^?1). In the absence of mechanical agitation similar lipase yields were achieved but in less time, resulting in productivity, about 60% greater than in a stirred fermenter; the lower energy demand for the same lipase yield offers economic advantages. Copyright © 2004 Society of Chemical Industry     

Production of Lipase from Geotrichum candidum Using Corn Steep Liquor in Different Bioreactors

The production of an extracellular lipase using corn steep liquor (CSL) as the nitrogen source in the cultivation of Geotrichum candidum NRRLY‐552 was evaluated. The optimized conditions in shake flasks were CSL, 8.0 % w/v, soybean oil, 0.6 % w/v, pH 7.0, 30 °C, 250 rpm, and 48 h, resulting in a maximum lipase productivity of 0.438 U mL^?1 h^?1(U = the amount of enzyme required to liberate 1 μmol of fatty acid per minute). Scale‐up was evaluated with airlift and stirred tank reactors; the best conditions, respectively, were 1 vvm(volume of gas per volume of medium per minute) of aeration which resulted in 0.535 U mL^?1 h^?1 (32 h) and 1 vvm and 300 rpm resulting in 0.563 U mL^?1 h^?1 (16 h). To facilitate downstream processes, lipase production was also evaluated using CSL previously clarified with activated charcoal resulting in 0.275 U mL^?1 h^?1 (24 h) using 12 % (w/v) of clarified CSL in shake flasks. The obtained results showed that CSL leads to similar productivity compared to peptone using the same microorganism under similar conditions. In addition the cost of fermentation medium using CSL is much lower because it is a very inexpensive by‐product from corn processing.     

Xylitol production by Candida tropicalis from corn cob hemicellulose hydrolysate in a two‐stage fed‐batch fermentation process

BACKGROUND: Xylitol, a sugar alcohol widely used in food and pharmaceutical industries, can be produced through biological reduction of xylose present in hemicellulose hydrolysates by Candida tropicalis. However, the aeration rate and by‐products originating from hemicellulose hydrolysis strongly inhibit the production of xylitol in a fermentation process. A two‐stage fed‐batch fermentation system was developed to reduce these inhibitory effects and to improve xylitol production from corn cob hemicellulose hydrolysates by C. tropicalis. RESULTS: Results of batch fermentations indicated that high xylitol production could be obtained from C. tropicalis at an initial xylose concentration of 80 g L^?1 in corn cob hydrolysate medium at an aeration rate of 0.4 vvm at the micro‐aeration stage. In the two‐stage fed‐batch fermentation process, 96.5 g L^?1 xylitol was obtained after 120 h, giving a yield of 0.83 g g^?1 and a productivity of 1.01 g L^?1 h^?1, which were 12.16% and 65.57% higher than those in a batch fermentation. CONCLUSION: High xylitol production can be achieved in a two‐stage fed‐batch fermentation process, in which the negative effects of aeration rate and inhibitory compounds on xylitol formation can be considerably reduced. Copyright © 2011 Society of Chemical Industry     

Rheological studies on Streptomyces fradiae ScF-5 in submerged fermentation

Studies on the rheology of Streptomyces fradiae ScF-5 in a 10-dm³ submerged fermenter for the production of intracellular glucose isomerase revealed that the apparent viscosity of the broth increased with increase in cell density up to 24 h and then declined while the density of the broth remained constant. The plot of shear stress versus shear rate at various fermentation periods showed the applicability of the Casson model. The yield stress and consistency index were found to increase gradually then decrease subsequently. In contrast, the flow behaviour index was less than unity and remained constant throughout the fermentation. The results contrast with the findings of other workers on the Newtonian and non-Newtonian character of fermentation broths and the applicability of the power law model to such systems.     

Gas Holdup in Circulating Bubble Columns with Pseudoplastic Liquids

The contributions of pressure drop due to wall frictional losses to the total gas holdup of two‐phase viscous non‐Newtonian systems were experimentally investigated using a 150 dm³ circulating bubble column. The column had a downcomer‐to‐riser cross‐sectional area ratio of 0.54 and a dispersion height of 2.5 m. Aqueous solutions of xanthan gum and carboxymethyl cellulose were used to simulate a wide range of rheological properties. The average wall shear stress was estimated from Al‐Masry's (1999) correlation for the average wall shear rate in external loop airlift reactors. Pressure drop due to wall shear stress was found significantly contributed by 10–70 % to the total gas holdup. This contribution has always been ignored in the data presented in the literature due to the absence of reliable and simple correlations for the average shear rate and shear stress. Corrections to gas holdup were found necessary for non‐Newtonian solutions with concentrations of ≥ 0.5 wt/wt.‐%.     

Optimization of pullulan production using Ca‐alginate‐immobilized Aureobasidium pullulans by response surface methodology

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. Copyright © 2007 Society of Chemical Industry     

Determination of agitation and aeration conditions for scale-up of cellulolytic enzymes production by <Emphasis Type="Italic">Trichoderma inhamatum</Emphasis> KSJ1

10 to 35 L jar fermentation scale-up cultures were performed to determine the optimum agitation and aeration rates in the cellulolytic enzymes production culture by Trichoderma inhamatum KSJ1. The optimum agitation rate in the 35 L jar fermenter was provisionally determined to be 150 rpm by using a geometrically resembled scale up method from the 10 L jar fermenter. The optimum aeration rate was determined to be 0.5 vvm by applying the mean values of superficial velocity and vvm. The DO (Dissolved Oxygen) concentration of the culture liquid was maintained below the critical DO concentration (2.336 mg/L) at 150 rpm in the 35 L jar fermenter. To increase the DO above the critical DO concentration, the agitation rate was increased from 150 to 200 rpm, with the aeration rate maintained at 0.5 vvm. As a result, the DO was maintained above critical DO concentration. The OUR (Oxygen Uptake Rate) and k _L a values were 0.91 mg-DO/L·min and 11.1 hr⁻¹, respectively. The amylase and FPase (filter paper activity) activities were 4.48 and 0.74 U/mL, respectively, in the 35 L jar fermenter, which was comparable to that in the 10 L fermenter (4.2 and 0.5 U/mL, respectively). Therefore, the scale-up conditions, 0.5 vvm and 200 rpm, were concluded to be the optimum aeration and agitation rates in the 35 L jar fermenter.     

Combined Effect of Agitation/Aeration and Fed‐Batch Strategy on Ubiquin‐ one‐10 Production by Pseudomonas diminuta

The effects of aeration rate and agitation speed on ubiquinone‐10 (CoQ10) submerged fermentation in a stirred‐tank reactor using Pseudomonas diminuta NCIM 2865 were investigated. CoQ10 production, biomass formation, glycerol utilization, and volumetric mass transfer coefficient (k_La) were affected by both aeration and agitation. An agitation speed of 400 rpm and aeration rate of 0.5 vvm supported the maximum production (38.56 mg L^–1) of CoQ10 during batch fermentation. The fermentation run supporting maximum production had an k_La of 27.07 h^–1 with the highest specific productivity and CoQ10 yield of 0.064 mg g^–1h^–1 and 0.96 mg g^–1 glycerol, respectively. Fermentation kinetics performed under optimum aeration and agitation showed the growth‐associated constant (a = 5.067 mg g^–1) to be higher than the nongrowth‐associated constant (β = 0.0242 mg g^–1h^–1). These results were successfully utilized for the development of fed‐batch fermentation, which increased the CoQ10 production from 38.56 mg L^–1 to 42.85 mg L^–1.     

Non‐newtonian rheological behavior of semi‐dilute ultra‐high molecular weight polyethylene solution in gel‐spinning process. 1: Concentration effect on the fundamental rheological properties

The rheological properties of a semi‐dilute ultra‐high molecular weight polyethylene (UHMw‐PE)/paraffin wax solution were investigated by mainly focusing on the influence of its concentration on the shear flow viscosity. It was found that the UHMw‐PE solution exhibits a shear‐thinning behavior at a very wide shear rate range from 10^?4 to higher than 10³ sec^?1. Furthermore, this typical non‐Newtonian behavior was more obvious with a concentration increase. From the concentration dependence of the zero‐shear creep compliance or other rheological factor, it was found that the extremely large M_e value of the system gives rise to various kinds of non‐Newtonian behaviors, especially those highly elastic in nature. Finally, the origin of the abnormal stress fluctuation during the steady shear measurement was found to be related to the shear‐induced structural development of the solution.     

Effects of morphology and oxygen supply on schizophyllan formation by Schizophyllum commune using a pellet size controlling bioreactor

The effects of mycelial morphology and oxygen supply on the production of the anti‐tumor polysaccharide from Schizophyllum commune were evaluated in this study. A pellet size controlling bioreactor has been used successfully for the production of the anti‐tumor polysaccharide of S commune. The average pellet size of mycelia in a bubble column bioreactor was around 20.5 mm in a typical run without using pellet size control. By forcing the fermentation broth through a pellet size control device with a stainless screen at five different fermentation times ranging from 1.0 to 4.5 days in each batch, different fungal pellet sizes ranging from 12.3 to 3.0 mm were achieved. The formation of anti‐tumor polysaccharide, schizophyllan (SPG), was significantly associated with the pellet morphology and oxygen supply rate. An optimal product yield of 0.29 g g^?1 glucose was obtained when the pellet size was controlled at 12.3 mm. Oxygen transfer limitation inside the pellets was responsible for the formation of entrapped polysaccharide. Maximum entrapped SPG yield (Yp/s entrapped) of 0.88 g g^?1 glucose occurred at the optimal pellet size of 12.3 mm. Copyright © 2005 Society of Chemical Industry     

Rheological and morphological properties of submerged citric acid fermentation broth in stirred-tank and bubble column reactors

Rheological data for beet molasses broth with Aspergillus niger in pellet form are reported for the biomass developed in a large number of experiments in a 50 l bubble column reactor and a 5 l stirred-tank reactor. The results are summarized in two typical time courses for batch fermentation. Morphological differences caused by the different shear fields in the two reactors are reflected in the rheological differences. The non-Newtonian properties of the whole fermentation broth depend entirely on the concentration and morphology of the biomass since the liquid phase is a low viscosity Newtonian fluid.     

Pilot-scale production of bacterial cellulose by a spherical type bubble column bioreactor using saccharified food wastes

Bacterial cellulose (BC) was produced by Acetobacter xylinum KJ1 in a modified airlift-type bubble column bioreactor, which had a low shear stress and high oxygen transfer rate (k _L a). Saccharified food wastes (SFW) were used as the BC production medium due to its low cost. An aeration rate of 1.2 vvm (6 L/min) was tentatively determined as the optimal aeration condition in a 10 L spherical type bubble column bioreactor, by analysis of the oxygen transfer coefficient. When 0.4% agar was added, the BC production reached 5.8 g/L, compared with 5.0 g/L in the culture without the addition of agar. The BC productivity was improved by 10% in the addition of 0.4% agar into the SFW medium. Then, by conversion of a linear velocity of 0.93 cm/sec, from the relationship between the linear velocity and oxygen transfer rate, 1.0 vvm (30 L/min) was determined as an optimal aeration condition in a 50 L spherical type bubble column reactor. Using SFW medium, with the addition of 0.4% agar, and air supplied of 1.0 vvm, 5.6 g/L BC was produced in the 50 L spherical type bubble column bioreactor after 3 days of cultivation, which was similar to that produced in the 10 L bioreactor. In conclusion, the addition of agar, a viscous polysaccharide, into SFW medium is effective for the production of BC, and this scale-up method is very useful for the mass production in a 50 L spherical type bubble column bioreactor by decreasing the shear stress and increasing the k _L a.     

Scaling up the Bioconversion of Cheese Whey Permeate into Fungal Oil by Mucor circinelloides

The bioconversion of hydrolyzed whey permeate into an oil-rich biomass by Mucor circinelloides was scaled up from 250 mL to 4 L with the use of an aerated stirred tank bioreactor. Biomass production and oil accumulation were strongly influenced by agitation speed (99–451 rpm) and aeration rate (0.29–1.70 vvm). Higher agitation and aeration rates (e.g., >400 rpm, >1 vvm), resulted in significantly higher biomass yield due to increased oxygen transfer capabilities and better mixing. Additionally, oil accumulation in the fungal biomass was related to high agitation (>400 rpm), while aeration (0.5–1.5 vvm) had no significant effect within the range evaluated. The predictive model was validated at the optimal conditions of 450 rpm and 1 vvm. Maximum biomass yield of 10.7 g L⁻¹ and lipid content of 32% dry biomass were achieved during 120 hours of fermentation. Simultaneous optimization of agitation and aeration in a bioreactor was found to not only improve fungal growth but also lipid content (24% vs. 32%), lipid yield (2.2 vs. 3.1 g L⁻¹) and γ-linoleic production (73–464 mg L⁻¹) compared to that of shake-flask. This study resulted in a scaled-up and optimized fermentation process that increased production of M. circinelloides biomass for subsequent use as raw material for food, feed, and fuel applications. This signifies a starting point for further studies aimed at assessing the development of a fully functioning fungi-to-food/fuel system on an industrial scale for several agricultural streams.     

Liquid circulation time in concentric-tube airlift columns with non-newtonian fermentation broths

Liquid circulation times were measured in a 40-dm³ concentric-tube airlift fermenter with simulated media over a wide range of rheological properties. Circulation times decreased with increasing shear-thinning, and the influence of draft-tube geometry on circulation time was found to depend on the shear-thinning of the media. A semi-theoretical correlation for both Newtonian and non-Newtonian fermentation media was developed.     

Optimization of citric acid production by <Emphasis Type="Italic">Aspergillus niger</Emphasis> NRRL 567 grown in a column bioreactor

Citric acid production using Aspergillus niger NRRL 567 grown on peat moss has been optimized in a column bioreactor using a statistically based method. A 23 full factorial design with eight fermentation conditions was applied to evaluate significance on citric acid production and their interactions between variables, where the three independent variables evaluated were aeration rate, bed depth and temperature. Aeration rate and fermentation temperature were identified to be significant variables. Citric acid production markedly increases with aeration rate and fermentation temperature; however, the bed depth of solid substrate showed an insignificant effect on citric acid production. The optimum fermentation condition for citric acid production in a column bioreactor consisted of aeration rate of 0.84 vvm, bed depth of 22 cm and fermentation temperature of 32 °C. Under a given condition, a maximum citric acid production of 120.6 g/l was predicted and matched well with the experimental value of 123.9 g/kg.     

Hydrodynamic behaviour and oxygen transfer rate in a pilot plant fermenter. I. Influence of viscosity

The effects of varying impeller speed, aeration rate and viscosity on mixing time, power consumption and oxygen transfer rate were studied in the pilot plant fermenter. The rheological behaviour of erythromycin fermentation broth was simulated by colloidal starch solutions at apparent viscosities of 0.02–0.20 Pa/s. The volumetric oxygen transfer rate coefficient was determined by the sulphite and static method. The experimental results showed that at low viscosities, up to of 0.02 Pa/s, the suitable range of impeller speed is 250–300 min^?1 at aeration rate 0.6–0.8 VVM from the point of view of power input (2.6–2.8 kW/m³) and sufficient coefficient K_La (160–200 h^?1). At viscosities higher than 0.02 Pa/s (with pseudoplastical character) the suitable range of impeller speed is 300–350 min^?1 at the same aeration rate. Then the power input for mixing is 3.0–3.5 kW/m³ and the coefficient K_La ～ 50 h^?1.     

Hydrodynamic behaviour and oxygen transfer rate in a pilot plant fermenter: I. Influence of viscosity

The effects of varying impeller speed, aeration rate and viscosity on mixing time, power consumption and oxygen transfer rate were studied in the pilot plant fermenter. The rheological behaviour of erythromycin fermentation broth was simulated by colloidal starch solutions at apparent viscosities of 0.02–0.20 Pa/s. The volumetric oxygen transfer rate coefficient was determined by the sulphite and static method. The experimental results showed that at low viscosities, up to of 0.02 Pa/s, the suitable range of impeller speed is 250–300 min^?1 at aeration rate 0.6–0.8 VVM from the point of view of power input (2.6–2.8 kW/m³) and sufficient coefficient K_La (160–200 h^?1). At viscosities higher than 0.02 Pa/s (with pseudoplastical character) the suitable range of impeller speed is 300–350 min^?1 at the same aeration rate. Then the power input for mixing is 3.0–3.5 kW/m³ and the coefficient K_La ～ 50 h^?1.     

Rheological characterization of dextran-enzymatic synthesis media

The bacteria Leuconostoc mesenteroides (strain NRRL-B512) has been used for the fermentative production of the polysaccharide dextran from sucrose. The polysaccharide production was carried out via a four-step process involving (1) production of the enzyme dextransucrase (DS), (2) bacteria removal from the culture broth, (3) enzyme purification by gel permeation chromatography, and (4) enzymatic synthesis of dextran in a cell-free reaction medium. The enzymatic reaction was followed measuring the change in rheological properties of the reaction medium with time at different initial substrate concentrations. The influence of other parameters, such as temperature, addition of acceptor molecules (maltose), and enzyme purity, were also considered. The microbial extracellular polysaccharide is responsible for the non-newtonian character of the reaction media. At low shear rate values the flow behavior was newtonian, whereas at higher shear rates the reaction media exhibited a marked shear-thinning behavior. The Carreau equation appears to fit fairly well the experimental data over several decades of shear rate. The reaction media showed elastic behavior as well.     

Rheological and mechanical properties of thermoplastic polyurethane elastomer derived from CO2 copolymer diol

CO₂ copolymer diol‐based thermal polyurethane elastomers (PPC‐TPU) were prepared by the reaction of CO₂ copolymer diol and methylene diphenyl diisocyanate and chain extender (ethylene glycol/1,4‐butanediol/1,6‐hexanediol) (EG/BDO/HG). The rheological and mechanical properties of PPC‐TPU were analyzed. The effects of shear rate, shear temperature, hard segment content, and variety of chain extender on the properties of PPC‐TPU were studied. The results showed that the apparent viscosity (η) of PPC‐TPU decreased with the increasing shear rate (τ), and the non‐Newtonian index (n) was less than 1. PPC‐TPU exhibited a typical character of pseudoplastic non‐Newtonian rheological behavior. The degradation during the processing was obviously inhibited by adding plasticizer and antioxidant. It was also discovered that the apparent viscosity varied with the content of hard segment and chain extender. Under the same temperature (185 °C) and shear rate (50 s^?1), the apparent viscosity increased considerably with the raise of hard segment content, and the apparent viscosity and tensile strength of PPC‐TPU with EG as chain extender was the maximum. It can be seen that with the apparent shear rate increasing, the variation tendency of apparent shear stress levels off, and the nonlinear relationship of τ–γ curve tended to be obvious. PPC‐TPU exhibited a typical character of pseudoplastic non‐Newtonian rheological behavior. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45974.