bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Novel Extractive Fermentation Process for Propionic Acid Production from Whey Lactose
Authors: Lewis Vivian P. , Yang Shang‐Tian 
Published: March 2005

AbstractAn extractive fermentation process was developed to produce propionate from lactose. The bacterium Propionibacterium acidipropionici was immobilized in a spiral wound, fibrous matrix packed in the reactor. Propionic acid is the major product from lactose fermentation, with acetic acid and carbon dioxide as byproducts. Propionic acid is a strong inhibitor to this fermentation. A tertiary amine was used to selectively extract propionic acid from the bioreactor, hence enhancing reactor productivity by over 100 %. We also speculate that by selectively extracting propionic acid, lactose metabolism can be directed to yield more propionate and less byproducts. Other advantages of extractive fermentation include better pH control (by removing acid products) and a purer product. The propionic acid present in the extractant can be easily stripped with small amounts of an alkaline solution, resulting in a concentrated propionate salt. The extractant was also regenerated in this stripping step. Thus, the process is energy‐efficient and economically attractive.
Glass Transition in Poly(vinylpyrrolidone): Effect of Molecular Weight and Diluents
Authors: Buera Maria Del Pilar , Levi Guy , Karel Marcus 
Published: March 2005

AbstractAmorphous poly(vinylpyrrolidone) (PVP) varying in molecular weight (MW) (10 000, 24 000, and 40 000) was used to study the effect of molecular weight on the glass transition temperature (Tg). Tg was measured by differential scanning calorimetry (DSC). Blends with several diluents (water, butylamine, glycine, hexanal, xylose, glucose, and lysine) were also analyzed and the effect of blend composition on Tg was evaluated. The effect of average molecular weight and of composition in the blends of PVP‐plasticizer on Tg was well described by previously reported relationships developed for synthetic polymers. The quantitative results obtained can be used for formulation of mixtures with known Tg and for prediction of their behavior in storage.
Prediction of pH in Model Systems Pressurized with Carbon Dioxide
Authors: Meyssami Behrouz , Balaban Murat O. , Teixeira Arthur A. 
Published: March 2005

AbstractMathematical models were developed to predict the pH of model liquid food systems (pure water, ascorbic acid‐water, citric acid‐water, and ascorbic acid‐citric acid‐water) pressurized with carbon dioxide, as functions of pressure (0–34.50 MPa), temperature (32,37, and 42° C), and component concentrations [(0–1.107) X10−3 M for ascorbic acid, (0 to 6.080) × 10−4 M for citric acid]. For all simulation systems, predicted pH values closely followed experimentally measured pH values. In the pure water‐CO2 systems, pH was a strong function of pressure but a weak function of temperature. In ascorbic acid‐water‐CO2, citric acid‐water‐CO2, and ascorbic acid‐citric acid‐water‐CO2 systems, pH was relatively insensitive to CO2 pressure and was a strong function of acid concentrations. This method could be a first step toward predicting the pH of orange juice and other liquid food systems under pressurized CO2.
Designing Enzymes for Use in Organic Solvents
Authors: Dordick Jonathan S. 
Published: March 2005

AbstractEnzymes are routinely used in organic solvents where numerous reactions of interest to synthetic and polymer chemists can be performed with high selectivity. Recently, it has become apparent that the catalytic properties of an enzyme can be tailored to a specific catalytic requirement by the use of solvent and protein engineering. The former involves altering the polarity, hydrophobicity, water content, etc., of the organic milieu, while the later applies site‐directed mutagenesis to alter the physicochemical properties of the biocatalyst. The dominant effects of organic solvents on enzyme structure and function, and the potential of solvent and protein engineering to design enzymes to function optimally in organic media, are the major foci of this review.
Bioprocess Development To Improve Foreign Protein Production from Recombinant Streptomyces
Authors: Delacruz Neslihan , Payne Gregory F. , Smith Jeffrey M. , Coppella Steven J. 
Published: March 2005

AbstractBioprocessing strategies to improve production of the heterologous protein parathion hydrolase from recombinant Streptomyces lividans were investigated. Initial limitations to increased production were overcome by using large amounts of nutrients and feeding these nutrients throughout the fermentation. Batch addition of such large amounts of nutrients resulted in byproduct acid accumulation. Our data suggest that byproducts resulted from incomplete utilization of peptide medium ingredients and not from an overflow of glucose catabolism. Over extended fed‐batch operation, oxygen transfer became limiting and these limitations were overcome by sparging oxygen‐enriched gas. When cultivation was continued past about 90 h, we observed that despite nutrient feeding and oxygen enrichment enzyme activities no longer increased. Our results show that during such late cultivation periods the rates of enzyme synthesis and deactivation became balanced. If synthesis is prevented, either by a nutritional limitation or by the addition of the protein synthesis inhibitor chloramphenicol, enzyme activities were observed to decrease. Since deactivation rate constants in these experiments were similar to those observed in cell‐free studies, and because extracellular protease activities were not detected in our fermentation, it appears that deactivation results from the inherent instability of the parathion hydrolase enzyme.
Bioreactor Scale‐Up for the Oxygen‐Sensitive Culture Bacillus subtilis: The Influence of Stirrer Shaft Geometry
Authors: Bourne John R. , Zurita Eddy P. , Heinzle Elmar 
Published: March 2005

AbstractThe relative amounts of the metabolites acetoin and 2,3‐butanediol, formed in a Bacillus subtilis culture, depend strongly on the dissolved oxygen concentration (DO). Hence any factor determining DO can influence the product ratio Ac/Bu. Experiments in a 0.045 m3 stirred bioreactor, fitted with three Rushton turbines, have shown different product ratios when the diameter of the drive shaft was changed and all other conditions were kept constant. This unexpected result was attributed to changes in the power consumption and the pumping and gas handling capacities of the turbines. B. subtilis was cultivated in three geometrically similar vessels (0.045, 0.45, and 4.5 m3) using a constant superficial gas velocity (0.0075 m s−1). The product ratio and the volumetric mass transfer coefficient were essentially independent of scale when the gassed power input per unit volume was constant. This scale‐up result reflects the importance of adequate oxygenation of this culture, which was violated when the shaft diameter was not scaled with the vessel diameter. Geometrical similarity was an important factor in the scale‐up of this fermentation.
On the Theoretical Determination of Optimal Times for Biomass Production in Batch Cultures of Aggregate‐Forming Cells
Authors: Silva Teresa R. , Malcata F. Xavier 
Published: March 2005

AbstractA model based on transient substrate and population balances coupled with Monod kinetics for growth has been formulated using several simplifying assumptions for batch cultures of cells which form biomass aggregates. The functional form of the analytical solution of this system of equations in its most generic aspect has been obtained and applied in the calculation of the time period corresponding to the maximum average rate of biomass increase.
Optimization of Growth Methods and Recombinant Protein Production in BTI‐Tn‐5B1‐4 Insect Cells Using the Baculovirus Expression System
Authors: Wickham T. J. , Nemerow G. R. 
Published: March 2005

AbstractA novel insect cell line from Trichoplusia ni, BTI‐Tn 5B1‐4 (Tn 5), was compared to Spodoptera frugiperda, Sf 9, cells for production of two recombinant secreted proteins: truncated Epstein‐Barr viral attachment protein (EBV gp105) and truncated, soluble tissue factor (sTF). Under optimum conditions for both cell lines, Tn 5 cells produced 28‐fold more secreted sTF than Sf 9 cells, respectively, on a per cell basis. The total production of gp105 was similar for the two cell lines. However, Tn5 cells secreted gp105 much more efficiently, resulting in 5‐fold higher levels in the extracellular medium. Despite these increases, Tn 5 cells are attachment‐dependent, and protein production is sensitive to the cell density (cells/cm2), unlike the Sf9 cell line which can be easily grown and scaled up in cell suspension cultures without significantly affecting its per cell production. Thus, protein production from Tn 5 cells above 0.1L scales was optimized with respect to cell density using standard techniques for the growth of attachment‐dependent cells. Roller bottles precoated with DEAE‐based microcarriers and suspension cultures employing collagen‐coated microcarriers were found to be effective ways of culturing Tn 5 cells. Predetermined optimal cell densities were used to produce EBV gp105 in microcarrier‐coated roller bottles or in suspension cultures using collagen‐coated microcarriers at concentrations close to those observed in tissue culture flasks.
The Change of Pressure Drop during Large‐Scale Chromatography of Viscous Samples
Authors: Felinger Attila , Guiochon Georges 
Published: March 2005

AbstractThe variation of the inlet pressure during the injection and the elution of a band of a viscous compound, or pressure‐drop profile, was calculated in overloaded elution chromatography, assuming a significant difference between the viscosities of the solvent and the pure solute. The viscosity of the mixture was calculated using the Grunberg—Nissan equation. By means of the numerical integration of the mass balance equation, the concentration profile along the length of the column was calculated. Then, using the instantaneous concentration profile to derive the local viscosity, hence the local pressure gradient, the pressure drop was determined by integrating the local pressure gradient along the column. The change of pressure drop calculated is significant only when the concentration of the injected sample is very high. If a dilute sample is injected, even large sample volumes will not really change the pressure drop. The maximum pressure drop observed in each case is practically independent of the absorption isotherm. The only determining factors are the solute concentration in the sample, the amount of sample injected, and the solute diffusivity.
A Study of Process Interactions between Cell Disruption and Debris Clarification Stages in the Recovery of Yeast Intracellular Products
Authors: Clarkson Andrew I. , Lefevre Patrick , Titchener‐Hooker Nigel J. 
Published: March 2005

AbstractThe effects of varying the levels of cell disruption achieved by high‐pressure homogenization upon subsequent centrifugal separation of cell debris have been defined by measuring sedimentation velocity distributions of the cell debris. Using this data together with particle size distributions, a computer‐based model of a disk stack centrifuge has been used to predict the efficiency of centrifugal separation. These predictions have been compared with both laboratory scale and pilot plant scale experimental results. A similar sedimentation velocity technique has been used to characterize the properties of the floes formed by addition of poly (ethylene imine) to a borax‐clarified homogenate supernatant. The variations of floe settling properties with respect to polymer concentration are defined.
Crossflow Microfiltration of Yeast Suspensions in Tubular Filters
Authors: Redkar Sanjeev G. , Davis Robert H. 
Published: March 2005

AbstractCrossflow microfiltration experiments were performed on yeast suspensions through 0.2‐μm pore size ceramic and polypropylene tubes at various operating conditions. The initial transient flux decline follows dead‐end filtration theory, with the membrane resistance determined from the initial flux and the specific cake resistance determined from the rate of flux decline due to cake buildup. For long times, the observed fluxes reach steady or nearly steady values, presumably as a result of the cake growth being arrested by the shear exerted at its surface. The steady‐state fluxes increase with increasing shear rate and decreasing feed concentration, and they are nearly independent of transmembrane pressure. The steady‐state fluxes for unwashed yeast in deionized water or fermentation media are typically 2–4 times lower than those predicted by a model based on the properties of nonadhesive, rigid spheres undergoing shear‐induced back‐diffusion. In contrast, the steady‐state fluxes observed for washed yeast cells in deionized water are only 10–30% below the predicted values. The washed yeast cells also exhibited specific cake resistances that are an order of magnitude lower than those for the unwashed yeast. The differences are due to the presence of extracellular proteins and other macromolecules in the unwashed yeast suspensions. These biopolymers cause higher cell adhesion and resistance in the cake layer, so that the cells at the top edge are not free to diffuse away. This is manifested as a concentration jump from the edge of the cake layer to the sheared suspension adjacent to it. The shear‐induced diffusion model includes a dimensionless parameter (referred to as the crossflow integral) that accounts for the concentration jump as well as the viscosity and diffusivity properties of a given suspension, and this parameter was determined for the unwashed yeast suspensions by fitting the experimental flux data to the model. The resulting values of this parameter are significantly lower than those for rigid spheres but show relatively little variation between experiments at different operating conditions for a given filter, indicating that the parameter is an intrinsic property of the suspension/membrane system. However, a significant difference in the parameter values was obtained between the ceramic and polypropylene membranes, indicating that the adhesive and fouling properties of the cake depend on the membrane material with which it is in contact. The resulting fluxes obtained from the model using single values for the membrane resistance, specific cake resistance, and crossflow integral for each data set (ceramic and polypropylene filters) are in good agreement with the measured fluxes. Inertial lift theory with no adjustable parameters was also compared to the data. It was found to overpredict the steady‐state fluxes at high shear rates and underpredict the fluxes at low shear rates.
Liquid‐Liquid Extraction of a Recombinant Protein with a Reverse Micelle Phase
Authors: Pires M. J. , Cabral J. M. S. 
Published: March 2005

AbstractRecombinant cytochrome bs was extracted to a reversed micelle phase of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) in cyclohexane/decanol and back‐extracted to a fresh aqueous phase. Depending on the experimental conditions, i.e., temperature, pH, and ionic strength, the extraction is controlled by either hydrophobic (pH close to the pI and high ionic strength) or electrostatic (pH far from the pI and low ionic strength) interactions. The protein interacts strongly with the surfactant aggregate once it is extracted to the organic phase, and it is very difficult to back‐extract it to a new aqueous phase.
Competitive Immunosorbent Assays for Biotin Using Bifunctional Unilamellar Vesicles
Authors: Jones Matthew A. , Kilpatrick Peter K. , Carbonell Ruben G. 
Published: March 2005

AbstractCompetitive immunosorbent assays for the model antigen biotin were performed using both unilamellar vesicles with covalently attached biotin and horseradish peroxidase (HBVs) and commercially available biotin‐labeled horseradish peroxidase (B‐HRP) as the enzyme‐labeled antigen. The assays were performed using anti‐biotin antibody (ABA) surface densities ranging from one‐tenth to full monolayer coverage. It was found that assays using HBVs strongly depended on the antibody surface density, while assays using B‐HRP were relatively insensitive to the antibody surface density. The HBV assay dependence on the ABA surface density was most likely due to multiple point attachment of vesicles to the surface. The lowest detectable antigen concentration (least detectable dose) foT vesicles (∼ 10−9 M) was an order of magnitude lower than the value found for B‐HRP (∼ 10−8 M). The sensitivity (slope of the response vs biotin concentration curve) of assays with B‐HRP was comparable to the sensitivity of assays with HBVs at low antibody surface density, probably due to less extensive multipoint attachment. It was also found that assays could be performed with vesicles at antibody surface densities that were at least 5 times lower, in terms of the bulk antibody concentrations used to coat the wells, than antibody surface densities at which B‐HRP gave comparable signals (∼1 ΔA/min).
Solvent Selection and Productivity in Multiphase Biotransformation Systems
Authors: Santhanam Harish K. , Shreve Gina S. 
Published: March 2005

AbstractThe 11‐β hydroxylation of the steroid precursor Reichstein's substance S (cortexolone) to hydrocortisone by Curvularia lunata cells is used as a model system for investigating the basis of the effect of solvent choice on multiphase biotransformation reaction kinetics. The effect of solvent choice and phase ratio on cellular toxicity and productivity is examined in batch suspension cultures. In general, the greater the miscibility of the solvent with the aqueous phase, the more cellular toxicity it exhibits. However, the presence of solvent at concentrations above the solubility limit showed no increased toxic effect over that achieved with saturation concentrations. Toxicity experiments indicate that of the solvents examined octane is the least toxic to the Curvularia lunata substance S biotransformation system under consideration. The production of hydrocortisone is determined to be approximately 20 times greater during the growth phase than during the stationary phase. The phase ratio of the organic solvent added has a significant effect on the productivity of the system. It was found that there is an increase in productivity with an increase in the phase ratio of the organic solvent added. Reaction kinetics are examined, and the increase in productivity with increasing amounts of organic solvent is attributed to the increase in concentration of the steroid reactant in the system.
Enzymatic Esterification of Diols in Reverse Micellar Media
Authors: Yang Ching‐Lun , Gulari Erdogan 
Published: March 2005

AbstractWith the help of highly dynamic reverse micellar media, lipase‐catalyzed esterification reactions can be carried out at ambient conditions without any agitation. Having low water contents in reverse micellar media, these reversible reactions favor the esterification direction instead of the normal hydrolysis catalyzed by lipases. A proposed enzyme kinetic model has successfully predicted the reaction mechanism of lauric acid with 1,3‐propanediol in reverse micellar media. However, experiments conducted showed a likelihood of substrate inhibition at higher lauric acid concentrations (>70 mM) and a strong bonding effect among 1,3‐propanediol, water, and AOT head groups. The effect of water concentration in the reaction media was shown to be important. The optimal Wo's for achieving the greatest initial reaction rate and final conversion were 9 and 4 for Candida rugosa and Rhizopus delemar, respectively. For both lipases, reverse micellar media experiments showed a lipase localization possibility.
On‐Line Exhaust Gas Analysis of Volatiles in Fermentation Using Mass Spectrometry
Authors: Oeggerli A. , Heinzle E. 
Published: March 2005

AbstractLiquid‐phase concentrations of volatile compounds were determined on‐line via gasphase analysis using mass spectrometry. It has been shown theoretically as well as experimentally that almost every volatile compound commonly produced by microorganisms can be measured by the method presented, if its partial pressure in the fermentor off‐gas exceeds 1 μbar. This has been shown in a baker's yeast as well as a Bacillus subtilis culture. The experimental results also indicated that these measurements are not controlled by mass‐transfer kinetics. A dimensionless parameter, E, allows us to check whether the analysis is determined by thermodynamics (Henry coefficient) or by mass‐transfer rates.
Fractal Analysis of Antigen‐Antibody Binding Kinetics: Biosensor Applications
Authors: Sadana Ajit , Ram Aruna Beela 
Published: March 2005

AbstractThe diffusion‐limited binding kinetics of antigen (or antibody) in solution to antibody (or antigen) immobilized on a biosensor surface is analyzed within a fractal framework. The estimated fractal dimension increases linearly from 2.28 to 2.75 for the antirabbit IgG (antibody) (Nygren, H.; Stenberg, M. J. Colloid Interface Sci. 1985, 107, 560–566) as the R1S1 antibody concentration in solution increases 28‐fold from 6 to 170 μg/mL‐Similarly, for the binding of ferritin (antigen) in solution by a “sandwich” immunoassay to antiferritin (antibody) immobilized on a surface (Bluestein, B. I.; Craig, M.; Slovacek, R., Stundter, L.; Urciuoli, C; Walizak, I.; Luderer, A. In Biosensors with Fiberoptics; Wise, D., Wingard, L. B., Jr., Eds.; The Humana Press, Inc.: Clifton, NJ, 1991; pp 181–223), the estimated fractal dimension decreases from 1.33 to 1.02 as the initial concentration of ferritin increases from 20 to 1000 μg/mL. The analysis attempts to provide novel physical insights into the reactions occurring on the surface and the structure or nature of the surface. Diffusional limitations inherent in such systems need to be uncoupled from reaction kinetics and complexities, such as heterogeneity, that exist on the surface.
Energetic Effect of Vitreoscilla Hemoglobin Expression in Escherichia coli: An On‐Line 31P NMR and Saturation Transfer Study
Authors: Chen Ruizhen , Bailey James E. 
Published: March 2005

AbstractA newly developed on‐line 31P NMR system has been used to investigate the effect of Vitreoscilla hemoglobin (VHb) expression on the steady‐state level of ATP in Escherichia coli under oxygen‐limited conditions. The VHb‐expressing strain GR021 exhibited a higher growth rate on a minimal fed‐batch medium after the onset of oxygen limitation and maintained the same level of ATP pool and transmembrane ΔpH as the slower growing wild‐type strain MG1655, indicating that the net ATP accumulation rate (the rate at which ATP increases per unit volume of culture per unit time) was enhanced in the VHb‐expressing strain. Further direct evidence of the enhanced flux of Pi‐ATP (catalyzed by ATPase) in GR021 was obtained in a saturation transfer study on respiring cells. VHb‐expressing cells respiring on succinate exhibited a Pi‐ATP flux 30 ± 5% higher than that of an otherwise isogenic strain that did not express VHb.