Showing papers in "Bioprocess and Biosystems Engineering in 2001"
TL;DR: In this article, four different processes for butanol production from corn, namely, batch fermentation and distillative recovery (BFDR), batch fermentation, BFPR, fed-batch fermentation and pervaporative recovery, and ICCFPR, were evaluated.
Abstract: Four different processes for butanol production from corn, namely, batch fermentation and distillative recovery (BFDR), batch fermentation and pervaporative recovery (BFPR), fed-batch fermentation and pervaporative recovery (FBFPR), and immobilized cell continuous fermentation and pervaporative recovery (ICCFPR) were evaluated. Pervaporative recovery significantly reduces the cost of butanol production. Depending upon the byproduct credit, which is approximately 3.7 times that of the amount of butanol produced, BFDR, BFPR, FBFPR, and ICCFPR result in a butanol price of $0.55, $0.14–0.39, $0.12–0.37, and $0.11–0.36×kg–1, respectively. The price of butanol was recently reported at $1.21×kg–1 by Chemical Marketing Reporter. It should be noted that all three components (acetone, butanol, and ethanol: ABE) diffuse through the pervaporation membrane. Further separation and purification of the solvents would require distillation, which has been considered in this exercise. This article also details the impact of byproduct credit, rate of return, and tax on butanol price.
79 citations
TL;DR: In this paper, a hybrid method based on evolutionary algorithms is developed to estimate the parameters of the Monod model of a recombinant fermentation process, which can fit the experimental observations satisfactorily.
Abstract: A hybrid method based on evolutionary algorithms is developed in this study. Two additional operations, an acceleration operation and a migration operation, are embedded into the original version of differential evolution. These two operations are used for the improvement of the convergence speed without decreasing the diversity among the individuals. The acceleration operation is used to speed up convergence. However, the migration operation is used to increase the diversity among the individuals. The hybrid method is applied to estimate the parameters of the Monod model of a recombinant fermentation process. The model profiles based on ±50% variations of the initial concentrations of glucose can fit the experimental observations satisfactorily.
53 citations
TL;DR: Culture conditions in growth and esterase production by a newly isolated Lactobacillus casei CL96 were investigated and the enzyme activity was maximal at pH 7.0 and 37°C, which might be suitable for biotechnological applications in the dairy industry.
Abstract: Culture conditions in growth and esterase production by a newly isolated Lactobacillus casei CL96 were investigated using a dextrose-free MRS medium supplemented with different sugars in a 2 l fermentor at different pHs (4.0–9.0) and temperatures (20–50°C). The optimal growth was obtained in basal MRS medium containing 1% (w/v) lactose at pH 7.0 and 30°C. The maximal esterase production was obtained intracellularly during the late logarithmic phase, but during the stationary phase, the esterase activity was released in the culture medium. The enzyme activity was maximal at pH 7.0 and 37°C. Among various substrates (C2–C16) tested, the highest activity was towards C6 and C8. Though the enzyme was produced constitutively, the tributylin induced the enzyme production by 2.5 fold. L. casei CL96 esterase was very active at neutral pH and ambient temperature and might be suitable for biotechnological applications in the dairy industry.
52 citations
TL;DR: In this paper, a diamond attenuated total reflection element was evaluated at pilot scale for the quantitative measurement of fermentation analytes using Fourier transform mid-IR spectrometry, which was shown to be stable, unaffected by reactor operation conditions of agitation, airflow, and backpressure, but sensitive to temperature control.
Abstract: Robust in situ biochemical monitoring is essential for the development of substrate feed control to optimize fermentation processes. The scale up of the fermentation for the fungus Glarea lozoyensis can benefit from such technology to improve the yield of the pharmaceutically important pneumocandin of interest and control the levels of unwanted analogues. A new in situ probe, using a diamond attenuated total reflection element, was evaluated at pilot scale for the quantitative measurement of fermentation analytes using Fourier transform mid-IR spectrometry. The new technology was shown to be stable, unaffected by reactor operation conditions of agitation, airflow, and backpressure, but sensitive to temperature control. Both glucose and phosphate were simultaneously monitored during a seed fermentation at 280 L pilot scale using complex medium with detection to 0.1 g/L for both analytes. Fructose, glutamate, and proline were monitored at 75 L scale using production media with detection limits of 0.1, 0.5, and 0.5 g/L respectively. Partial least squares calibration/prediction models were created for analytes of interest using off-line reference measurements and specific spectral regions. Good fits were obtained between off-line measurements and those predicted by in situ mid-IR. Standard errors of prediction (SEP) for glucose (range 18–0.1 g/L) and phosphate (range 11–7.5 g/L) were 0.16 and 1.8 g/L respectively with mean percentage errors (MPEs) around 2.5%. SEP values for the production process: fructose (range 20–0.1 g/L), glutamate (8–0.5 g/L), and proline (12–0.5 g/L) were 0.44, 0.6, and 0.5 g/L respectively with MPEs of 2.2, 5.3, and 10.1%. The technology effectively demonstrates quantitative multicomponent analysis of fermentation processes using in situ monitoring.
46 citations
TL;DR: In this paper, an experimental design-based medium optimization was carried out for the production of poly-β-hydroxybutyrate (PHB) by Azotobacter beijerinckii in shake flasks.
Abstract: The competition between the biodegradable polyhydroxyalkanoates (PHA) and petrochemical plastics could be in terms of cost of production. Also, the impact of PHA on the preservation of the environment has been established in detail. Efforts in the direction of obtaining cheaper raw materials could reduce the cost of production of PHA. Therefore, an experimental design-based medium optimization was carried out for the production of poly-β-hydroxybutyrate (PHB) by Azotobacter beijerinckii in shake flasks. Previous reports have not indicated the application of corn-steep liquor (CSL) as the nitrogen source. Thus attempts were made for the production of PHB using CSL and molasses as the carbon source. It was observed that the combination of molasses and CSL could be used in its production. Analysis of the experimental data has shown the optimum concentration to be 65.4 g/l of molasses and 13.2 g/l of CSL. Also, untreated molasses resulted in a higher yield in comparison with potassium-ferrocyanide-treated molasses, indicating the contribution of unidentified components favouring the growth and yield of PHB by Azotobacter beijerinckii.
40 citations
TL;DR: Secretory production of human granulocyte colony-stimulating factor fusion protein (hG-CSF) by fed-batch culture of Escherichia coli was investigated in both 2.5-L and 30-L fermentors and the constant feeding strategy supported best hG- CSF production.
Abstract: Secretory production of human granulocyte colony-stimulating factor fusion protein (hG-CSF) by fed-batch culture of Escherichia coli was investigated in both 2.5-L and 30-L fermentors. To develop a fed-batch culture condition that allows efficient production of hG-CSF, different feeding strategies including pH-stat, exponential and constant feeding were examined. Among these, the constant feeding strategy (0.228 g glucose×min–1) and the exponential feeding that supports a low specific growth rate (µ=0.116 h–1) resulted in the best hG-CSF production. Under these conditions, 4.4 g×L–1 of hG-CSF was produced. The effect of induction time on the protein production was also investigated. For the fed-batch cultures carried out with the pH-stat and exponential feeding strategies, induction at higher cell density (late-exponential phase) resulted in more hG-CSF production compared with induction at lower cell density (early to mid-exponential phase). The constant feeding strategy that supported best hG-CSF production was applied to the scale-up production of hG-CSF in 30 L of fermentor. The maximum dry cell weight and hG-CSF concentration of 51.7 and 4.2 g×L–1, respectively, was obtained.
37 citations
TL;DR: The microbial community composition differed considerably between the two reactors as determined by fluorescent in situ hybridisation (FISH) with rRNA-targeted oligonucleotide probes, and the relative abundance of ammonia and nitrite oxidisers measured by FISH was consistent with results from dynamic simulation of the nitrification process.
Abstract: Nitrification performance of a chemostat and a membrane-assisted bioreactor (MBR) was assessed at pilot scale for the treatment of sludge reject waters with NH4
+–N concentrations up to 600 mg/L and low organic content (COD<200 mg/L). To prevent nitrifier washout the 1-m3 chemostat was operated at 20°C with minimum hydraulic retention time of τ=2 days. At the 0.71 m3 MBR, τ was successively reduced to 6.2 h. Complete sludge retention was achieved by means of a 2-m2 100,000-Dalton PES ultrafiltration membrane. Operation in crossflow mode with flow velocities from v
F=2.4–3.7 m/s and transmembrane pressures Δp=0.5–1.2 bar yielded a long-term permeate flux of 110 L/(m2×h). In the MBR, nitrification rates up to 2,500 g N/(m3×d) were measured with biomass concentrations between 4 and 15 g TSS/L. Despite low TSS values, about 0.2 g/L of the chemostat was able to nitrify 180 g N/(m3×d). The microbial community composition differed considerably between the two reactors as determined by fluorescent in situ hybridisation (FISH) with rRNA-targeted oligonucleotide probes. For both reactors, the relative abundance of ammonia and nitrite oxidisers measured by FISH was consistent with results from dynamic simulation of the nitrification process.
36 citations
TL;DR: In this paper, a continuous foam separation column was examined and the effects of the operating factors, superficial air velocity, feed flow rate, feed concentration and pH on the above characteristics was investigated.
Abstract: Enrichment and recovery of bovine serum albumin has been examined in a continuous foam separation column. The effects of the operating factors, superficial air velocity, feed flow rate, feed concentration and pH on the above characteristics was investigated. The protein enrichment decreased with the increase in the value of each of these parameters. Protein recovery increased with increasing air velocity, decreased with increasing feed flow rate and did not change very much with increasing feed concentration. Maximum protein recovery was obtained at the isoelectric point (pH 4.8) of the protein. Maximum protein recovery was found to be a strong function of the air velocity in the range 0.05–0.15 cm/s. Further increase in air velocity did not have much effect on recovery because of very large bubbles formed as a result of coalescence. Bubble size was determined as a function of the above factors in the liquid and foam sections of the column. It was found to be dependent on protein concentration, feed flow rate and solution pH. The effect was more significant in the foam section of the column. The bubbles in the foam section were significantly larger (about 3–10 times) than those in the liquid, with a sharp change at the foam-liquid interface. The bubble size measurements were used to calculate the interfacial area and it was shown that the rate of protein removal increases with increasing interfacial area.
33 citations
TL;DR: In this paper, a model of the formation of primary gas bubbles at the static sparger (sinter plate) of small-scale bubble columns and a common mass-transfer correlation for bubbles rising in a non-coalescent Newtonian electrolyte solution of low viscosity is presented.
Abstract: Volumetric oxygen transfer rates and power inputs were estimated by a model of the formation of primary gas bubbles at the static sparger (sinter plate) of small-scale bubble columns and a common mass-transfer correlation for bubbles rising in a non-coalescent Newtonian electrolyte solution of low viscosity. Estimations were used to assess the dimensioning and possibilities of small-scale bubble column application with an height/diameter ratio of about 1. Estimations of volumetric oxygen transfer rates (<0.16 s–1) and power inputs (<100 W m–3) with a mean pore diameter of the static sparger of 13 µm were confirmed as function of the superficial air velocity (<0.6 cm s–1) by measurements using an Escherichia coli fermentation medium. Small-scale bubble columns are thus to be classified between shaking flasks and stirred-tank reactors with respect to the oxygen transfer rate, but the maximum volumetric power input is more than one magnitude below the power input in shaking flasks, which is of the same order of magnitude as in stirred-tank reactors. A small-scale bubble columns system was developed for microbial process development, which is characterized by handling in analogy to shaking flasks, high oxygen transfer rates and simultaneous operation of up to 16 small-scale reactors with individual gas supply in an incubation chamber.
30 citations
TL;DR: Though the cause of aggregation at this stage is not clear, aerobic metabolism appears to be required and the increase in size was indeed due to aggregation, probably due to physico-chemical affects such as hydrophobicity or charge interactions.
Abstract: Previous work has shown that in many mycelial fermentations the predominant morphological form is clumps (aggregates) which cannot be further reduced by dilution. During fermentation, the clump size and shape is affected by fragmentation, which in turn depends on agitation conditions. This paper addresses the question of whether mycelial aggregation can also occur during a fermentation. The dynamics of changes in mycelial morphology due to aggregation were investigated in 5.3-L chemostat cultures of Aspergillus oryzae by imposing a step decrease in agitation speed from 1,000 to 550 rpm under conditions of controlled non-limiting dissolved oxygen tension, with a steady-state biomass concentration of 2 g/L. The mean projected area (size) of the mycelia, measured using image analysis, increased from 5,300±400 µm2 (at 1,000 rpm) to 9,400±900 µm2 (at 550 rpm). This change occurred too rapidly for it to be solely caused by mycelial growth. Instead, it is proposed that the increase in size was indeed due to aggregation, probably due to physico-chemical affects such as hydrophobicity or charge interactions. Aggregation was also shown to occur in 4-L aerated batch cultures at higher biomass concentrations (5.3 and 11.2 g/L) in which the agitation speed was decreased from 1,100 to 550 rpm. Experiments were also conducted off-line in a mixing vessel in the absence of oxygen. In this case, aggregation was not observed. Thus, though the cause of aggregation at this stage is not clear, aerobic metabolism appears to be required.
29 citations
TL;DR: A balance between model accuracy and mathematical tractability was obtained to facilitate the formulation of the control algorithm and a time-delay compensator was built into the control law to account for the observed 90-min lag associated with GFP fluorescence.
Abstract: A model-based control algorithm (generic model control) is presented for fed-batch cultivation of recombinant Escherichia coli producing either transcriptional or translational fusion products. With the recent development of translational and operon fusions using green fluorescent protein (GFP) [Albano et al. (1998) Biotechnol Prog 14:351–354] along with an on-line GFP sensor [Randers-Eichhorn et al. (1997) Biotechnol Bioeng 55:921–926], real-time measurements of foreign protein level are now possible. A mathematical model is presented that is both accurate and simple so as to ensure that all state variables remain observable during cultivation. A balance between model accuracy and mathematical tractability was obtained to facilitate the formulation of the control algorithm. Generic model control (GMC) is a process model-based control algorithm incorporating a process model directly within the control structure. GMC was desirable since linearization of the process model was not necessary and robust performance could be obtained despite process disturbances or plant/model mismatch. Furthermore, a time-delay compensator was built into the control law to account for the observed 90-min lag associated with GFP fluorescence. The feasibility of the GMC algorithm was demonstrated by simulations.
TL;DR: In this article, a full-bridge sensor system for characterising biosuspensions by impedance spectroscopy which avoids cross-sensitivity to temperature is presented, where frequency is varied between 500-kHz and 50-MHz.
Abstract: A full-bridge sensor system for characterising biosuspensions by impedance spectroscopy which avoids cross-sensitivity to temperature is presented. To record a large range of different kinds of cells, frequency is varied between 500 kHz and 50 MHz. The characteristic frequencies of the β-polarisation of animal cells (mouse), yeasts (Saccharomyces cerevisiae) and Escherichia coli bacteria are located in this range. The widespread applicability of this method is demonstrated by measurements on suspensions of different cells and the determination of concentration in a fermentation process. Furthermore, yeast suspensions are characterised at temperatures between T
1=24°C and T
2=36°C to evaluate the influence of temperature. A reduction of cross-sensitivity of about one order of magnitude compared to a single-sensor results. Changing in the conductivity of the suspension by 26% alters the measured biomass concentration by only 2.8%.
TL;DR: In this article, a smoothing estimator based on backward and forward extended Kalman filtering is proposed for the specific growth rate of Bordetella pertussis and Neisseria meningitidis.
Abstract: For modelling purposes it is of great importance to derive the specific growth rate as a function of time from biomass measurements. Traditional methods such as exponential or polynomial fitting do not give satisfactory results nor do these methods take the noise characteristics of the biomass measurements into account. Standard recursive techniques, such as Kalman filtering, use only the data up to the time under consideration and are dependent of a good initial estimation. This paper describes a technique based on combining subsequent backward and forward extended Kalman filtering to give a smoothing estimator for the specific growth rate. The estimator does not need an initial value and is shown to have a single tuning parameter. The applicability of the estimator is demonstrated on batch and fed-batch cultivations of two organisms: Bordetella pertussis and Neisseria meningitidis.
TL;DR: In this article, a novel, centrifugal, packed-bed reactor (CPBR) during viscous xanthan fermentation was determined with respect to the effects of the arrangement of the centrifugal packed bed (CPB) and the recirculation loop (RL).
Abstract: The oxygen transfer properties of a novel, centrifugal, packed-bed reactor (CPBR) during viscous xanthan fermentation were determined with respect to the effects of the arrangement of the centrifugal, packed bed (CPB) and the recirculation loop (RL). Characterized by the maximum volumetric transfer coefficient (k L a) in xanthan broth, the aeration efficiency of CPBR was compared to those in stirred-tank reactors (STR) equipped with disc turbines (DT) or marine propellers (MP), and to that in a water-in-oil emulsion (WIO). As expected, STR-WIO showed the highest k L a (0.038 s–1 at 2%) among all systems studied due to reduced broth viscosity; however, practical difficulties exist in product recovery. It was found that, at 3.5% xanthan the k L a in CPBR (0.018 s–1) was higher than that of STR (0.005 s–1) and close to that of STR-WIO (0.020 s–1), indicating improved oxygen transfer at such a xanthan concentration. The exterior baffles along the rotating fibrous matrix offer additional agitation in the viscous broth. A gas-continuous arrangement, in which the CPB was kept above the broth, was able to elevate k L a to 0.023 s–1, higher than that of STR-WIO. The external RL operated by a peristaltic pump was found to play an important role in CPBR aeration by providing better gas–liquid contact. With the improved oxygen transfer efficiency in CPBR at high xanthan concentrations, the CPBR system is practically the preferred system for xanthan fermentation. The characteristic roles of CPB arrangement and the RL should be considered primarily during scale-up operation.
TL;DR: In this paper, the branching structure of potato amylopectin was modeled in a computer matrix and the chain-length distribution and the length and width of a cluster of the molecule were used as input variables in the model.
Abstract: The branched structure of potato amylopectin (degree of polymerization ~200,000) was modeled in a computer matrix. The chain-length distribution and the length and width of a cluster of the amylopectin molecule were used as input variables in the model. Independent literature values related to the structure of amylopectin (percentage β-hydrolysis and ratio of A- to B-chains) were used for evaluation of the branching characteristics (length of branch area and chance of branching) of the modeled amylopectin. The structural parameters predicted by the model agreed very well with data from the literature. The chain-length distribution and values for the percentage of β-hydrolysis were the two most important parameters required to model the structure of amylopectin. This computer-generated model of potato amylopectin in solution can be used to simulate various enzymatic (i.e., α-amylase, β-amylase, glucoamylase, pullunanase) or chemical reactions (i.e., acid hydrolysis, hypochlorite oxidation). The modeling approach described in this paper is also suitable for starches from other botanical sources (i.e., corn, wheat, tapioca).
TL;DR: In this article, a kinetic model of biological oxidation of the organic fraction of municipal solid waste suspension is presented, and the relation between a maximum specific growth rate and temperature is mathematically described.
Abstract: The kinetic model of biological oxidation of the organic fraction of municipal solid waste suspension is presented in this paper. The whole process of the aerobic biodegradation consists of three phases: the hydrolysis and intensive biodegradation phase, the limited biodegradation phase and the terminal phase. The first two phases play the most important role and the unstructured model is applied to successfully describe them. Kinetics of microbial decomposition of organic substances is described by the Monod equation. Also, a strong influence of temperature on the process kinetics is observed. The relation between a maximum specific growth rate and temperature is mathematically described.
TL;DR: The long-term process for producing human granulocyte-colony stimulating factor was developed using two-stage cyclic fed-batch culture, in which hG-CSF expressing-recombinant Escherichia coli was directed by an L-arabinose promoter system.
Abstract: The long-term process for producing human granulocyte-colony stimulating factor (hG-CSF) was developed using two-stage cyclic fed-batch culture, in which hG-CSF expressing-recombinant Escherichia coli was directed by an L-arabinose promoter system For the optimization, the preinduction growth rate during the growth stage and the feeding strategy during the production stage were investigated The maximum harvest volume during the production stage was predicted before long-term cyclic operation Based on those optimized strategies, the two-stage cyclic fed-batch culture was performed for 12 cycles (86 h) The cell growths in both stages were maintained at 45–50 g/L and 71–77 g/L, respectively hG-CSF was stably produced at a level of 8–9 g/L and the plasmid stability was maintained at more than 90% Volumetric productivity by the two-stage cyclic fed-batch culture was 0643 g/L/h, which was about 280% higher than that of conventional DO-stat fed-batch culture
TL;DR: Removal of tann in aqueous media containing tannic acid and condensed tannin substrates using heme peroxidases of Phanerochaete chrysosporium was studied and chemical oxygen demand was reduced.
Abstract: Removal of tannin from different tannin substrates using heme peroxidases of Phanerochaete chrysosporium was studied. Complete removal of tannin components in spent tan liquor was observed after 24 h of incubation with peroxidases. Tannin in aqueous media containing tannic acid and condensed tannin substrates were removed by 65.70±0.97 and 52.43±0.83%. Chemical oxygen demand was reduced by 24.38±0.73, 33.22±0.20, and 58.94±0.07%, respectively, in spent tan liquor, tannic acid and condensed tannin substrates containing aqueous media.
TL;DR: A model based on laboratory data for the synthesis of recombinant β-galactosidase was corrupted by adding imperfect mixing and noise in the feed stream to generate data mimicking a real nonideal operation, and it was seen that a hybrid network provides more accurate estimates of both extra-cellular and intra- cellular variables.
Abstract: Fermentations employing genetically modified microbes under industrial conditions are difficult to monitor on line or to describe by simple, good mathematical models. So, a practically convenient approach is to combine mathematical models of some aspects with artificial neural networks of those aspects which are difficult to measure or model. Such hybrid models have been applied earlier to laboratory-scale bioreactors. In the present work, a model based on laboratory data for the synthesis of recombinant β-galactosidase was corrupted by adding imperfect mixing and noise in the feed stream to generate data mimicking a real nonideal operation. These data were used to train a recurrent Elman neural network and a hybrid neural network, and it was seen that a hybrid network provides more accurate estimates of both extra-cellular and intra-cellular variables. The benefit is enhanced by the hybrid network's superiority being more pronounced for the intra-cellular recombinant protein, β-galactosidase, which is the main product of interest.
DSM1
TL;DR: Based on experimental results of eight fed-batch fermentations using a recombinant L-phenylalanine-producing Escherichia coli strain, the applicability of principal-component analysis (PCA) for fermentation analysis was studied.
Abstract: Based on experimental results of eight fed-batch fermentations using a recombinant L-phenylalanine-producing Escherichia coli strain, the applicability of principal-component analysis (PCA) for fermentation analysis was studied. Three principal components were identified, representing approximately 90% of total variance. Among them, concentrations of tyrosine and acetate were identified as key fermentation parameters. Their significance was also confirmed when measurement errors were taken into consideration by Monte-Carlo estimations. The error estimation approach was also used to investigate PCA suitability for the time-specific analysis of different fermentation phases. Relatively large principal-component score errors were calculated that limit the applicability of PCA for detailed fermentation course analysis.
TL;DR: A rigorous probabilistic framework for the reconciliation of apparently conflicting data from various physical and chemical measurements related to the key biological variables of alcoholic fermentation: the ethanol and the residual sugar concentrations is established.
Abstract: The paper establishes a rigorous probabilistic framework for the reconciliation of apparently conflicting data from various physical and chemical measurements related to the key biological variables of alcoholic fermentation: the ethanol and the residual sugar concentrations. The analysis is carried out on a database consisting of 15 beer fermentation experiments, for which off-line determinations of ethanol concentration, fermentable sugar concentration, wort density and refractive index are available, as well as on-line records of evolved CO2. The basic reconciliation method uses mass balance and monotonicity constraints derived from the biological knowledge of the fermentation process. In order to provide interpolated values and rate estimates, smoothness requirements are added. The reconciliation procedure gives more reliable estimates than any given measurement, detects outliers, helps fixing problems in the experimental setting and is also applicable on line.
TL;DR: In this article, a macroporous poly(glycidyl methacrylate, triallyl isocyanurate, divinylbenzene) was prepared by a radical suspension copolymerization.
Abstract: Macroporous poly(glycidyl methacrylate–triallyl isocyanurate–divinylbenzene) was prepared by a radical suspension copolymerization. Reaction of the copolymer with 2-hydroxyethyl amine was employed to obtain a hydrophilic matrix. An affinity dye, Cibacron blue 3GA, was then coupled covalently to prepare a novel macroporous affinity adsorbent. The surface and pore structure of the affinity adsorbent were examined by scanning electron micrography (SEM). SEM observations showed that the affinity adsorbent abounded in macropores. Bovine serum albumin (BSA) and lysozyme (Lys) were used as samples to examine the adsorption properties of the adsorbent. Under appropriate conditions, the affinity adsorbent had a capacity of 15.5 mg BSA/g and 22.3 mg Lys/g (wet adsorbent weight). The adsorbed proteins could be desorbed by increasing liquid phase ionic strength or by using a NaOH solution, and the adsorbent could be recycled for protein adsorption.
TL;DR: In this paper, a steady-state nonlinear feedforward controller for measurable disturbances is designed for a continuous bioreactor, which is represented by Hammerstein type nonlinear model wherein the nonlinearity is a polynomial with input multiplicities.
Abstract: A steady-state nonlinear feedforward controller (FFC) for measurable disturbances is designed for a continuous bioreactor, which is represented by Hammerstein type nonlinear model wherein the nonlinearity is a polynomial with input multiplicities. The manipulated variable is the feed substrate concentration (Sf) and the disturbance variable is the dilution rate (D). The productivity (Q=DP) is considered as the controlled variable. The desired value of Q=3.73 gives two values of feed substrate concentration. The nonlinearity in the gain is considered for relating output to the manipulated variable and separately for the relation between output to disturbance variable. The FFC is also designed for the overall linearized system. The performance of the FFC is evaluated on the nonlinear differential equation model. The FFC is also designed for the model based on a single nonlinear steady-state equation containing both D and Sf. This nonlinear FFC gives the best performance. The nonlinear FFC is also designed by using only linear gain for the disturbance and nonlinear gain for the manipulated variable. Similarly, nonlinear FFC is also designed by using linear gain for the manipulated variable and the nonlinear gain for the disturbance variable. The performances of these FFC schemes are compared.
TL;DR: Refolding was found to be unaffected by temperature between 30 and 50°C, giving 100% recovered specific activity, and a number of compounds were added to the mobile phase to reduce the relative viscosity between the sample and mobile phase.
Abstract: The influence of several parameters on the gel filtration refolding of hen egg white lysozyme from a starting concentration of 40 mg/ml was investigated. Refolding was found to be unaffected by temperature between 30 and 50°C, giving 100% recovered specific activity. At 10°C a 20% reduction in refolding yield was observed. Refolding was carried out successfully with both acrylamide (Sephacryl S100)- and dextran (Superdex 75)-based gel media. At the isoelectric pH of lysozyme, aggregation was suppressed in the column method, whereas protein aggregates were formed during dilution-based refolding. A number of compounds (carboxymethyl cellulose, dextran, sucrose) were added to the mobile phase to reduce the relative viscosity between the sample and mobile phase. Only sucrose, up to 20% (wt), was found not to interfere with lysozyme refolding.
TL;DR: In this paper, a split-cylinder air-lifted reactor is proposed, in the interior of which two multi-perforated vertical baffles are installed in order to provide several points of communication between the reactor riser and downcomer.
Abstract: Conventional airlift reactors are not adequate to carry out variable volume processes since it is not possible to achieve a proper liquid circulation in these reactors until the liquid height is higher than that of the downcomer. To carry out processes of variable volume, the use of a split-cylinder airlift reactor is proposed, in the interior of which two multi-perforated vertical baffles are installed in order to provide several points of communication between the reactor riser and downcomer. This improves the liquid circulation and mixing at any liquid volume.
TL;DR: In this article, the problem is converted into a nonsingular optimization problem of determining the optimal substrate concentration profile subject to a constraint, and an equivalent feed rate profile to match the optimal SCC profile is then generated.
Abstract: A new method to calculate the optimal feed rate profile for fedbatch culture is proposed Instead of the usual singular control approach of taking the feed rate as the control variable, the substrate concentration profile is used as the transformed control variable to avoid the computational difficulty associated with the singular control Thus, the problem is converted into a nonsingular optimization problem of determining the optimal substrate concentration profile subject to a constraint The equivalent feed rate profile to match the optimal substrate concentration profile is then generated With this method the computational difficulty associated with singular controls for high-order systems is circumvented The proposed method is illustrated by a number of examples
TL;DR: It has been demonstrated that, in addition to the increase in pac transcriptional and translational efficiency, the protein synthesis flux throughout pac expression steps should be balanced for enhancing the production of PAC in E. coli.
Abstract: The production of recombinant penicillin acylase (PAC) in Escherichia coli was optimized in this study. The effect of using a selection of host/vector systems as well as varying culture conditions on the production of PAC was investigated. The production of PAC based on the use of the native pac promoter was inefficient and could be significantly improved by using the strong trc promoter for regulation of pac expression. A mutant strain MDΔP7 was shown to be a suitable host for the production of PAC since the efficiency of both pac translation and posttranslational processing for MDΔP7 was significantly higher than that for the parent strain HBPAC101. However, the accumulation of inclusion bodies tended to limit the production of PAC as pac transcriptional and translational efficiency was increased. It has been demonstrated that, in addition to the increase in pac transcriptional and translational efficiency, the protein synthesis flux throughout pac expression steps should be balanced for enhancing the production of PAC in E. coli. With the optimization of the host/vector system and culture conditions, culture performance for the production of recombinant PAC was greatly improved. Process bottlenecks limiting the production of PAC were also discussed.
TL;DR: The Thiele modulus was found to drop out as a relevant parameter for the determination of the optimum concentration of the intermediate (reactant) species, although it plays a role in the best distribution of enzyme within the slab.
Abstract: A theoretical procedure is reported, which aims at finding the best molar distribution of two enzymes (considered equivalent and mutually exclusive in terms of occupancy of immobilisation sites), coimmobilised in a slab-shaped porous bead, that catalyse two sequential irreversible reactions (involving an initial reactant species, an intermediate species and a final product species, at 1:1:1 stoichiometry) following Michaelis-Menten kinetics. The mathematical derivation uses as objective function maximisation of yield of the final product on the initial reactant coupled with the maximum catalyst effectiveness. The Thiele modulus was found to drop out as a relevant parameter for the determination of the optimum concentration of the intermediate (reactant) species, although it plays a role in the best distribution of enzyme within the slab. Low values of k
cat for the first enzyme and high values of surface concentration of the initial reactant lead to small Thiele moduli; such diffusional regime promotes retention of product(s) within the porous matrix, thus providing opportunities for more complete conversion to the final product. The maximum yield of the final product corresponds to immobilising most of the first enzyme in the innermost portion of the slab and most of the second enzyme in the outermost portion.
TL;DR: A global inhibition function, η, was introduced to mathematically characterize this constraint based on thiodiglycol consumption and was used to optimize overall thiodiclycol degradation as well as define conditions for optimizing conversion to byproducts [(2-hydroxyethyl)thio]acetic acid (HETA) and thiodIGlycolic acid (TDGA), which are of commercial interest.
Abstract: A metabolic model was developed to describe the degradation of thiodiglycol (TDG) by Alcaligenes xylosoxydans ssp. xylosoxydans (SH91). Experimental evidence has suggested there is a metabolic capacity constraint that limits the specific thiodiglycol utilization rate, leads to metabolic byproducts, and ultimately inhibits the overall degradation process. A global inhibition function, η, was introduced to mathematically characterize this constraint based on thiodiglycol consumption. The resulting model described well the dynamic response of cells consuming thiodiglycol in several reactor configurations (batch, repeated batch, repeated fed batch) and was used to optimize overall thiodiglycol degradation as well as define conditions for optimizing conversion to byproducts [(2-hydroxyethyl)thio]acetic acid (HETA) and thiodiglycolic acid (TDGA), which are of commercial interest.
TL;DR: In this paper, the authors quantified the widely anticipated economic potential of fed-batch operation for a therapeutic product by flowsheet simulation and showed that the contribution from the product recovery section increased from 62% for base case to 77% for case A as the product concentration increased by fedbatch operation.
Abstract: The widely anticipated economic potential of fed-batch operation was quantified for a therapeutic product by flowsheet simulation. A process for production of t-PA from CHO cells based on fed-batch operation was compared to a base process that operates in batch mode. Two cases of fed-batch operation were considered, case A, where the product concentration was assumed to be four times the concentration obtained with base process and case B, where the concentration was eight times. The simulator, Bioprocess Simulator (BPS) from Aspen Technology, reported the final bioreactor volume and the total amount of the continuous feeds added during the fed-batch operation. BPS was also used to simulate the downstream processes. Comparison of the economic performances of the processes revealed that return on investment (ROI) of the base process would increase by 112% by switching to case A fed-batch operation from batch mode. Case B, on the other hand, would result in an increase of 288%. The importance of downstream processing for recovery of high-value products became apparent from this study. A breakdown of equipment purchase cost showed that the contribution from the product recovery section increased from 62% for base case to 77% for case A as the product concentration increased by fed-batch operation. For a fixed recovery of 40%, contribution from the downstream section was found to decrease to 70% for case B compared to case A. It was concluded from the results that higher product concentration would not result in proportionate increase in ROI because of limitations in the recovery section. A sensitivity analysis was carried out on several uncertainties of the simulated fed-batch process.