bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrolysis of liquefied corn starch in a membrane reactor
Authors: Sims Kevin A. , Cheryan Munir 
Published: December 2004

AbstractThe objective of this study was to develop a continuous hydrolysis process for the enzymatic saccharification of liquefied corn starch using a membrane reactor. A residence time distribution study confirmed that the membrane reactor could be modeled as a simple continuous stirred tank reactor (CSTR). Kinetic studies indicated that the continuous reactor operated in the first‐order region with respect to substrate concentration at substrate concentrations greater than 200 g/L. At a residence time of 1 h and an enzyme concentration of 1 g/L, the maximum reaction velocity (Vm) was 3.86 g glucose/L min and the apparent Michaelis constant (K) was 562 g/L. The K value for the continuous reactor was 2–7 times greater than that obtained in a batch reactor.Kinetic data were fit to a model based on the Michaelis‐Menten rate expression and the design equation for a CSTR. Application of the model at low reactor space times was successful. At space times of 6 min or less, the model predicted the reactor's performance reasonably well. Additional work on the detection and quantitation of reversion products formed by glucoamylase is required. Isolation, detection, and quantitation of reversion products by HPLC was difficult. Detailed analysis on the formation of these reversion products could lead to better reactor designs in the future.
Removal of dissolved metals by plant tissue
Authors: Scott Charles D. 
Published: December 2004

AbstractVarious types of microbial biomass have been shown to adsorb metals dissolved in aqueous media. It has now been demonstrated that certain plant tissues are also effective for this type of adsorption process. In particular, tomato and tobacco roots harvested from field‐grown plants were shown to adsorb Sr from an aqueous solution of SrCl2. Distribution coefficients in excess of 550 were measured and the adsorption isotherms at 25°C could be fitted to Langmuir‐type expressions. The bioadsorbent could be regenerated and metals recovered by either a reduction in the pH to less than 2.0 or by use of a concentrated chloride salt solution.
Effect of matrices on affinity purification of protein C
Authors: Kang Kyung , Ryu Dewey , Drohan William N. , Orthner Carolyn L. 
Published: December 2004

AbstractOne of the critical problems in scale‐up of affinity chromatography is the mechanical strength of the support matrix against pressure. Because the costs of both the gel matrix and the ligand for the affinity chromatography are very high, the reusability of gel matrices is directly related to the total production cost. In certain cases, where the source material is viscous (e.g., blood plasma), irreversible deformation of gel matrices can readily occur, necessitating severe constraints in the flow rate. Consequently, productivity is low.We have characterized the system parameters and investigated the performance of various matrices that are commercially available. The experimental system used for this study was the immunoaffinity purification of protein C (an anticoagulant protein) from human blood plasma. The support matrices studied were cross‐linked agarose, polymethyl acrylic, cellulose, and polyvinyl alcohol polymers. The major system parameters studied were pressure tolerance, coupling efficiency, adsorption efficiency, and batch adsorption/desorption kinetics of protein C to/from the monoclonal antibody (MAb)‐Matrix complex. In addition, the apparent equilibrium constant and bandwidth of the product concentration profile in the eluate were characterized by performing pulse tests.A methodology was developed for evaluating the immunoaffinity colum performance for the separation of protein C. By utilizing the experimentally measured parameters, the flow rate limitation for each purification step was computed. Then, the purification performance of the matrices were evaluated in terms of productivity per unit time. Among the matrices tested, cellulose was superior in overall performance for the immunoaffinity purification of protein C using a 10 cm × 10 cm column.
Culture instability of auxotrophic amino acid producers
Authors: Kiss Robert D. , Stephanopoulos Gregory 
Published: December 2004

AbstractThe long‐term dynamic characteristics of the L‐lysine producer Corynebcterium glutamicum in continuous culture were studied over a range of specific growth rates. The double‐auxotroph parent strain was found to be susceptible to a back mutation, or reversion, which negated the regulatory bypass that allows this strain to accumulate L‐lysine in culture but also gives rise to a L‐threonine auxotrophic requirement. Consequently, the revertant cells no longer over‐produced L‐lysine, nor were they limited in their growth by the low levels of L‐threonine in the medium. All continuous culture experiments were enventually taken over by these revertants. The instability of the culture was found to be primarily due to the growth rate differential between the two competing populations, the (productive) parent auxotrophs and the (nonproductive) revertants. A deterministic mathematical model of the culture dynamics, incoroporating two limiting‐substrate balances, satisfactorily described the takeover profiles. A linear stability analysis of the model equations identified that although long‐term culture demise is inevitable, the dimensionless ratio of the two limiting substrates controls the rate of takeover by nonproductive cells. The anslysis further demonstrated the importance of proper medium design in delaying the onset of takeover in cultures of this double‐auxotroph strain. The theoretical medium design criterion was then confirmed experimentally by the stabilization of a fed‐batch culture against revertant takeover for an extended fermentation time.
Fermentation kinetics of recombinant yeast in batch and fed‐batch cultures
Authors: Patkar Anant , Seo Jin‐Ho 
Published: December 2004

AbstractFed‐batch cultures of recombinant microorganisms have attracted attention as they can separate cell growth stage from cloned‐gene expression phase during fermentations. In this work, the effect of different glucose feeding strategies on cell growth and cloned gene expression was studied during aerobic fed‐batch fermentations of recombinant yeast, containing the plasmid pRB58. The plasmid contains the yeast SUC2 gene, which codes for the enzyme invertase. Some feeding policies resulted in a constant glucose concentration inside the fermentor, while others deliberately introduced a cyclic variation. The cell mass yield was found to be higher at low glucose concentrations, thus indicating a shift to the more energy‐efficient respiratory pathway. The SUC2 gene expression was derepressed at glucose levels below 2 g/L. The response of specific invertase activity to changes in the medium glucose concentration was found to be almost immediate.
Solubilization and growth of Candida pseudotropicalis in water‐in‐oil microemulsions
Authors: Pfammatter N. , Hochköppler A. , Luisi P. L. 
Published: December 2004

AbstractSome new aspects of microbiology in water‐in‐oil microemulsions are investigated using Candida pseudotropicalis in a hexadecane solution containing Tween85/Span80 (each 5% wt:wt) as surfactant, and limited amount of water (up to 3%, vol:vol), Microemulsion solutions containing cells up to 10 mg fresh weight per milliliter can be prepared, which display a greater time stability and a much smaller light scattering than aqueous suspensions having the same cell concentration. This is ascribed to a lower aggregation tendency of the cells in the microemulsion environment. It is also shown that C. pseudotropicalis cells are able to grow (up to a factor of approximately 6–7 within a few days) in the microemulsion system containing nutrient medium in the aqueous microphase; but they are also able to grow at the expense of the hexadecane. This is proved with radioactive‐labeled hexadecane by measuring the increase of radioactivity in the cells as well as the emission of 14CO2. The growth rate of the cells is then compared with the growth rate of cellular proteins during cell reproduction in the microemulsion system. Two regimes are observed: a first one, in which cells growth rate and protein growth rate proceed parallel to each other; and a second one (established after 0.5–1 day) characterized by depletion of proteins in the microemulsion system. The implications of these findings for cell metabolism in microemulsion and for possible biotechnological applications are discussed.
Effect of low serum concentrations (0%–2.5%) on growth, production, and shear sensitivity of hybridoma cells
Authors: van der Pol L. , Bakker W. A. M. , Tramper J. 
Published: December 2004

AbstractIn a stirred culture of hybridoma cells, the effects of serum reduction from 2.5% to 0% on growth and monoclonal antibody porduction have been investigated. The shear sensitivity of cells from the same culture has been tested in a bubble column. Serum reduction does not greatly affect viable‐cell concentrations, but cell specific monoclonal‐antibody production rate shows a decreasing trend. A gradual increase in sensitivity for sparging, which is nor the result of a long‐term biological effect, has beeen measured in a bubble column at decreasing fetal calf serum concentrations. Finally, the hypothetical killing‐volume model describing the death rate of insect cells in bubble columns has now been completely validated for the pertinent hybridoma‐cell line.
On‐line rheological measurements and control in fungal fermentations
Authors: Olsvik E. S. , Kristiansen B. 
Published: December 2004

AbstractA system for on‐line rheological measurements and control in filamentous fermentations is presented. The output signals from the control unit can be used in terms of process control. Diluting the broth in a growth controlled feed pattern was found to influence the viscosity of the broth and lead to process improvements. Just diluting the fermentation broth to keep the viscosity below a preset value was seen to give only temporary process improvements. The higher the viscosity, the less effective the viscosity controlled dilutions. The failure to get full control over the viscosity by the dilution techniques used is caused by the large number of factors influencing the rheological properties of an Aspergillus niger culture. The factors shown in this work to influence the rheological properties of the fermentation broth were the biomass concentration, the specific growth rate, mixing qualities (impeller speed and working volume), and the dissolved oxygen concentration. © 1992 John Wiley & Sons, Inc.
Effect of temperature on hybridoma cell cycle and MAb production
Authors: Bloemkolk Jan‐Willem , Gray Murray R. , Merchant Fahar , Mosmann Timothy R. 
Published: December 2004

AbstractThe kinetics of growth and antibody formation of an anti–interleukin‐2 producing hybridoma line were studied in suspension culture at temperatures ranging from 34°C to 39°C. Flow cytometry was used to determine the effect of temperature on the cell cycle. Maximum cell density and monoclonal antibody yield were observed at 37°C. The specific monoclonal antibody production rate was approximately constant throughout each batch experiment. Lower temperatures caused cells to stay longer in the G1‐phase of the cell cycle, but temperature had only a marginal effect on the specific antibody production rate. Arresting of cells in the G1‐phase by means of temperature was, therefore, not suited for enhanced monoclonal antibody production. Rather, antibody production for this hybridoma was directly linked to viable cell concentration. © 1992 John Wiley & Sons, Inc.
How to predict product yield in kinetically controlled enzymatic peptide synthesis
Authors: Gololobov Mikhail Yu. , Kozlova Elena V. , Borisov Ivan L. , Schellenberger Ute , Schellenberger Volker , Jakubke Hans‐Dieter 
Published: December 2004

AbstractThe published theory of kinetically controlled enzymatic peptide synthesis needed experimental verification. We carried out the measurement of the peptide yield and estimation of the key parameters α and β for papain‐catalyzed synthesis of Mal‐L‐Phe‐L‐Ala‐LLeuNH2 from Mal‐L‐Phe‐L‐AlaOMe and L‐LeuNH2. The experimental results demonstrate that this theory adequately describes the real process. © 1992 John Wiley & Sons, Inc.
Urea sensor with single poly(propylene) membrane
Authors: Wang Y. J. , Chen C. H. , Hsiue G. H. , Yu B. C. 
Published: December 2004

AbstractUrease was immobilized on the plasma‐aminated surface of a hyfrophobic poly(propylene) (PP) membrane. This membrane, with urease matrix on one side while maintaining its original hydrophobic property on the other, was used to construct the urea sensor. The new urea sensors had response sensitivities ranged from 19 mV/decade to 30 mV/decade depending on the conditions of the plasma reaction. The enzyme electrode using single membrane gave a shorter response time as compared to the corresponding conventional electrode employing two seperate PP membranes. The sensitivity of the enzyme electrode increased with increasing buffer pH and reached a maximal level (40 mV/decade) at pH 7.6. The response sensitivity of the electrode was not affected by the change of buffer strength. Deamination of the plasma‐modified hydrophobic PP membrane did not occur in aqueous environment judging from the stability of the urea electrode up to 12 days of operation. © 1992 John Wiley & Sons. Inc.
Efficient recovery of recombinant proteins using membrane‐based immunoaffinity chromatography (MIC)
Authors: Nachman Michele , Azad Abdul R. M. , Bailon Pascal 
Published: December 2004

AbstractA systematic approach to the design and development of membrane‐based immunoaffinity systems for the purification of recombinant proteins is presented. The preparation and characterization of immunoaffinity membranes are described. The immunoaffinity purification process for recombinant interferon‐α2a is used as a model system to determine the operational parameters in membrane‐based immunoaffinity chromatography. The high volumetric throughput of membranes, combined with the typically fastbinding kinetics of antigen‐antibody interactions, enable the purification of recombinant proteins from dilute feed stream in less time, using less antibody than conventional systems. Three recombinant proteins, human interferon‐α2a, interleukin‐2, and interleukin‐2 receptor, have been purified efficiently employing membrane‐based immunoaffinity chromatography. Overall, membrane‐based immunoaffinity chromatography is shown to be a viable and scalable method, ideal for the industrial‐scale production of recombinant proteins. © 1992 John Wiley & Sons, Inc.
Enzymatic resolution of racemic amines in a continuous reactor in organic solvents
Authors: Gutman Arie L. , Meyer Elazar , Kalerin Evgeny , Polyak Felix , Sterling Jeffrey 
Published: December 2004

AbstractAn enzymatic process has been developed for the continuous production of the pharmaceutically important intermediate (R)‐1‐aminoindan and of the chiral resolving agent (R)‐1‐(1‐naphthyl)ethylamine. The process consists of the subtilisin catalyzed stereoselective aminolysis of the racemic primary amine with an active ester in organic solvent. The competing nonenzymatic reaction has been suppressed by appropriate choice of solvent and reactant's concentration and by minimizing the time of contact between the amine and the active ester. Subtilisin was immobilized on glass beads and the reaction carried out in a continuous‐flow column bioreactor. By using a 450‐mL column bioreactor containing 5.7 g of subtilisin immobilized on 570 g of glass beads, 1.6 kg of racemic 1‐(1‐naphthyl)ethylamine was resolved after 320 h of continuous operation with only a slight loss of the enzymatic activity. During the whole process, the optical purity of the chiral amine eluting from the column was higher than 90%. A facile procedure was developed for separating the unreacted (R)‐amine from the (S)‐amide and for the recycling of the solvent 3‐methyl‐3‐pentanol and the active ester 2,2,2‐trifluoroethyl butyrate. © 1992 John Wiley & Sons, Inc.
Selective separation of microorganisms by lectins: Yeast and concanavalin A as a model system
Authors: Stratford Malcolm , Bond Chris J. 
Published: December 2004

AbstractSpecific 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.
Estimating cell concentration in the presence of suspended solids: A light scatter technique
Authors: Kennedy M. J. , Thakur M. S. , Wang D. I. C. , Stephanopoulos Gregory N. 
Published: December 2004

AbstractA novel sensor was developed, based on light scatter, to estimate the cell concentration in the presence of suspended solids. The light scatter properties of cells in the presence of suspended solids were investigated. Two crucial observations were made: first, that the light scatter from cells is essentially a linear function of cell concentration and, second, that invariant regions are present in the light scatter spectrum of cell/solid substrate mixtures. Invariant regions are wavelength intervals of the light scatter spectrum in which the light scatter reading is independent of solid substrate concentration and only a function of cell concentration. The occurrence of invariant regions is the key behavior which allowed the quantification of cell concentration in the presence of suspended solids.An algorithm was developed for the estimation, from light scatter data, of cell concentration in the presence of solid substrate. The light scatter approach was validated by comparing cell concentrations estimated by this technique to those obtained from DNA and carbon dioxide evolution rate measurements during a series of fermentations. The model system used was Bacillus subtilis var sakainensis ATCC 21394 growing on fishmeal as the sole nitrogen source.A model was developed based on the interactions of scatter and absorbance. This model reflects the hypothesis that invariant regions are caused by changes in the absorbance of the solid substrate as a function of wavelength. © 1992 John Wiley & Sons, Inc.
Damaging agitation intensities increase DNA synthesis rate and alter cell‐cycle phase distributions of CHO cells
Authors: Lakhotia Sanjay , Bauer Kenneth D. , Papoutsakis Eleftherios T. 
Published: December 2004

AbstractThe effects of fluid‐mechanical force (agitation) on the cell cycle kinetics of Chinese hamster ovary (CHO) cells cultured in suspension in 2‐L bioreactors has been examined. A two‐color flow cytometry method was used to determine the fraction rate of DNA synthesis. With increased agitation intensity, cell viability decreased as a result of increased cell death. However, increased agitation induced the viable cells of the culture to a higher proliferative state relative to a control culture. The fraction of viable cells of the high‐agitation culture (250 rpm) in S phase was higher (up to 45%) and in G1 phase was lower (up to 50%) compared with the viable cells of the control culture (80 rpm). The DNA synthesis rate per viable S‐phase cell of the high‐agitation culture was confirmed by recovery experiments, which were conducted to measure the apparent specific growth rate and the cell cycle kinetics of the high‐agitation culture upon reduction in the agitation rate from 250 rpm back to 80 rpm. The apparent specific growth rate of the test culture, calculated for the first 12 h of the recovery period, was greater than the apparent specific growth rate of the control culture. Furthermore, the proliferative state of the viable cells of the test culture, which had become higher relative to the control culture during the high agitation period, gradually approached the level of the control culture during recovery. Results also show that the magnitude of the agitation intensity; the culture agitated at 250 rpm attained a greater proliferative state than a parallel culture agitated at 235 rpm. The 250‐rpm culture had a higher fraction of S‐phase and a lower fraction of G1‐phase cells than the 235‐rpm culture. The DNA sunthesis rate per viable S‐phase cell of the 250‐rpm culture was greater than of the 235‐rpm culture. © 1992 John Wiley & Sons, Inc.
Development of a single‐pass ceramic matrix bioreactor for large‐scale mammalian cell culture
Authors: Applegate Mark A. , Stephanopoulos Gregory 
Published: December 2004

AbstractA single‐pass, plug‐flow bioreactor has been developed in which oxygen is supplied to entrapped hybridoma cells via sllicone tubes threaded through the square channels of a macroporous ceramic monolith. Oxygen diffuses from the gas phase, through the silicone tubing, across the open square channel, and into the pores of the ceramic wall where it is consumed by entrapped cells. Advantages of such a reactor include higher product yields, protection of cells from detrimental hydrodynamic effects, no internal moving parts to compromise asepsis, and simplicity of operation. A prototype bioreactor was constructed and operated over a range of residence times. A side‐by‐side experimental comparison with a conventional recycle bioreactor was performed by inoculating both bioreactors with cells from the same stock culture and feeding medium from the same reservoir. Final antibody titers were 80% higher in the single‐pass bioreactor at a residence time of 200 minutes compared with those of the recycle bioreactor at a residence time of 800 minutes. A theoretical analysis of oxygen transport in this bioreactor is developed to highlight important design criteria and operating strategies for scale‐up. © 1992 John Wiley & Sons, Inc.
Viability of Candida shehatae in D‐xylose fermentations with added ethanol
Authors: Kastner James R. , Ahmad Maqsood , Jones W. Jack , Roberts R. S. 
Published: December 2004

AbstractEthanol was added at concentrations of 25 and 50 g/L to active cultures of Canida shehatae under oxygen‐limited (fermentative) conditions. Added ethanol completely inhibited grwoth and fermentation of D‐xylose by C. shehatae. Cultures with added ethanol rapidly declined in cell viability as measured by plate counts and methylene blue staining. The rate of decline in cell viability was dependent on the amount of added ethanol. Over the course of the fermentation, cell viability, as measured by plate counts, was significantly lower in all experiments (with or without ethanol addition) compared with the viability measurements by methylene blue staining. Thus, data from the plate counts provided a more sensitive measure of the toxic effects of added ethanol and long‐term anaerobiosis on C. shehatae growth/fermentation. Mean cell volume and total cell volume declined in fermentations with added ethanol. © 1992 John Wiley & Sons, Inc.