bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selective adsorption of plant products
Authors: Payne G. F. , Shuler M. L. 
Published: December 2004

AbstractThe results from this study demonstrate that neutral resins can selectively concentrate specific indole alkaloids from dilute aqueous mixtures. Adsorption was observed to provide a one to two order of magnitude improvement in concentrating these alkaloids, as compared to an equivalent single‐staged extraction. Since the sorption correlates with the concentration of the neutral form of the dissolved alkaloid, the adsorption is dependent on both the pH of the medium and the pKa of the alkaloids. Also, adsorption is dependent on specific sorbent‐sorbate characteristics. In this study, by exploiting differences in the acid‐base properties and the sorption characteristics of specific indole alkaloids, separation factors of 20–30 were observed. Although this behavior is valuable for analytical separations, the present study considers the application to the primary recovery of alkaloids from plant cell processes. Throughout this study it was also observed that the polycarboxylic ester resin (XAD‐7) behaved quite differently from the styrene divinylbenzene resin (XAD‐4). Despite a lower capacity, the XAD‐7 resin was considerably more selective in adsorbing indole alkaloids than the XAD‐4 resin. These alkaloids could also be desorbed from the XAD‐7 resin by acidifying the liquid, while organic solvents were required to desorb these compounds from the XAD‐4 resin.
Anaerobic acidogenesis of a complex wastewater: II. Kinetics of growth, inhibition, and product formation
Authors: Dinopoulou Georgia , Sterritt Robert M. , Lester John N. 
Published: December 2004

AbstractThe kinetics of the acidogenic phase of anaerobic digestion were studied in continuous culture using a complex substrate based on beef extract. A number of different steady states was achieved covering a wide range of hydraulic retention times and product concentrations. The Monod equation failed completely to describe the growth of the acidogenic bacteria, while there was evidence of product inhibition. Therefore, two of the most commonly used inhibition models were applied, the non‐competitive and the Haldane‐type model. The former gave superior results, and the estimated values for the biokinetic constants were a maximum specific growth rate (μmax) of 32.6 day−1, a substrate saturation constant (Ks) of 1.77 g COD/L, an inhibition constant (Ki) of 0.633 g/L of total volatile fatty acids, and a specific decay rate (kd) 1.747 day−1. The same inhibition models were also applied to the description of the specific rate of product formation, with the noncompetitive model fitting the data slightly better. The maximum specific rate of product formation was estimated to be 125.7 g total volatile fatty acid/g biomass/day.
The anomaly of oxygen diffusion in aqueous xanthan solutions
Authors: Ho Chester S. , Ju Lu‐Kwang , Baddour Raymond F. 
Published: December 2004

AbstractA membrane‐covered polarographic oxygen electrode was used to measure oxygen diffusion coefficients in aqueous polyelectrolyte solutions of xanthan gum, sodium alginate, and sodium carboxymethylcellulose (CMC). In sodium alginate solutions, dilute xanthan solutions, and solutions containing more than 0.3 wt % CMC, oxygen diffusion coefficients decrease with increasing polymer concentrations. Interestingly, in dilute CMC solutions and concentrate xanthan solutions containing more than 0.5 wt % xanthan gum, oxygen diffusion coefficients increase with increasing polymer concentrations, and values exceeding that in pure water are generally observed.
A model of enzyme adsorption and hydrolysis of microcrystalline cellulose with slow deactivation of the adsorbed enzyme
Authors: Converse Alvin O. , Matsuno Ryuichi , Tanaka Mitsuo , Taniguchi Masayuki 
Published: December 2004

AbstractReduction in the activity and the concentration of the adsorbed enzyme are noted in the experimental data. Two alternative mechanisms, inactivation of the adsorbed enzyme and mass transfer of the enzyme from the bulk solution to the solution within the cellulose fibril where the cellulase is assumed to be inactive, are used to represent the decline in activity. The decline in concentration of the adsorbed enzyme is represented by a modest product inhibition and, more importantly, the assumption that the concentration of the adsorption sites is proportional to the square of the remaining substrate concentration. Measurements of both adsorbed enzyme and product concentration over time are used in determining parameter values. The model is applied to a series of experiments having a 10‐fold range of substrate concentration and to an experiment in which the product is removed continuously. For both deactivation mechanisms, a very good representation of product concentration (standard deviation 3.6%) is obtained over the full period (168 h) of hydrolysis; the representation of adsorbed enzyme is, however, less accurate (standard deviation 6.7–6.8%).
Monitoring electron transfer by photoacoustic spectroscopy in native and immobilized thylakoid membranes
Authors: Carpentier Robert , Leblanc Roger M. , Mimeault Murielle 
Published: December 2004

AbstractPhotoacoustic spectroscopy was used to monitor photo synthetic electron transfer in native and immobilized thylakoid membranes. The photoacoustic parameter ϕr′ (the percentage of absorbed energy that is stored in photo chemical intermediates) and i50 (the half‐saturation modulated light intensity) were directly correlated to electron transfer rates. As previously shown, thylakoids immobilized in an albumin‐glutaraldehyde matrix were more resistant to aging. The inhibitory effects of the immobilization procedure and of aging at 4°C were detected as a decrease in i50 values. In analogy with enzyme kinetic analysis, the effect could be characterized as a competitive type of inhibition. Photoacoustic measurements are performed in conditions similar to a working bioreactor cell with regards to the sample preparation.
Immobilization and kinetics of lactate dehydrogenase at a rotating nylon disk
Authors: Daka Joseph N. , Laidler Keith J. , Sipehia Rajender , Chang Thomas M. S. 
Published: December 2004

AbstractLactate dehydrogenase (LDH) was covalently attached to an impervious nylon surface by an improved technique. The procedure allowed the kinetics of the rotating enzyme disk reactor to be successfully explored. This enzyme‐disk configuration has potential applications in assays for lactic acid or pyruvic acid in fluids of biological importance (e.g., urine). In order to evaluate and understand the physics and chemistry underlying the kinetics of the heterogeneous biocatalyst, a mathematical model based on the von Karman‐Levich theories of rotating electrodes, was developed. It applied well to LDH attached to a disk, under variable NADH concentrations and fixed pyruvic acid. The new theory, leads to the conclusion that the apparent Michaelis constant Km(app), varies linearly with f‐1/2, where f is the speed of rotation of the disk. Extrapolation of f‐1/2 to zero gives the Michaelis‐Menten constant, Km, corresponding to the diffusion‐free behavior. With immobilized LDH, the diffusion‐free Km for NADH obtained at 25°C, in phosphate buffer (pH 7.5) using the extrapolation method was 84 μM. This value was in good agreement with the previously published value of 87 μM, obtained with LDH attached to the inner surface of a nylon tubing. However, when compared to the Km for a free enzyme system, the 84 μM was about nine times larger, indicating an inherent reduction in the activity of the bound LDH. Since, at extrapolated infinite rotation speeds, diffusion effects were assumed eliminated, the drop in the activity was thought to be due to sterric hinderances imposed on the substrate NADH as a result of having LDH bound to another polymer.
Stratified mixed‐culture biofilm model for anaerobic digestion
Authors: Canovas‐Diaz M. , Howell J. A. 
Published: December 2004

AbstractDevelopment of a novel two‐layer anaerobic biofilm model is based on substrate utilization kinetics and mass transport. The model is applied to steady‐state conditions for a fixed‐film anaerobic reactor. The microbial film is considered to consist of two distinct biofilm layers, one adjacent to the second, with an acidogenic bacteria biofilm forming the outer layer and a methanogenic film the inner one. The model assumes that sugars are only metabolized by the first layer and converted into volatile fatty acids (VFA), while fatty acids are taken up only by the inner layer. The model is able to predict both substrate flux net uptake and methane production for steady‐state conditions. The results of modeling agree with methane production experimental data published elsewhere. Further, the model shows why layered fixed‐film reactors can withstand high and inhibitory concentrations of volatile fatty acids as well as severe overloading without failure.
Computer modeling of antibiotic fermentation with on‐line product removal
Authors: Dykstra Kevin H. , Li Xiang‐Ming , Wang H. Y. 
Published: December 2004

AbstractThe fermentation of Streptomyces griseus for the production of cycloheximide is similar to other antibiotic fermentations in that product synthesis is subject to feedback regulation and the desired product is degraded in the fermentation broth. The productivity of this fermentation can thus be dramatically increased by removing the antibiotic from the whole broth as it is produced. One means for effecting this on‐line product removal is to contact the whole fermentation broth with neutral polymeric resin immobilized in hydrogel beads. The antibiotic adsorbs to the immobilized resin via hydrophobic interactions. In this work, the adsorption of the antibiotic onto the immobilized resin was characterized. A biochemical model of the fermentation was then used to describe the time profiles of biomass, substrate, and antibiotic in a fermentation system in which whole broth is circulated from the fermentor through a continuously stirred extractor containing the adsorbent beads. Various operating conditions were examined to optimize the productivity of the fermentation.
Oscillations in continuous cultures of budding yeast: A segregated parameter analysis
Authors: Porro Danilo , Martegani Enzo , Ranzi Bianca Maria , Alberghina Lilia 
Published: December 2004

AbstractSustained oscillations have been observed in continuous cultures of Saccharomyces cerevisiae. These oscillations appear spontaneously under aerobic conditions and may constitute a severe limitation for process control. We have found that oscillations arise only in a well defined range of dilution rates and dissolved oxygen values. The period of the oscillations is related, but not equal, to the mass doubling time, and shows a relation ship with both the parent cells and daughter cells generation times. At high dilution rates two oscillatory regimens, with different periods, are observed. The analysis of the budding index shows a marked degree of synchronization of the culture, however significant differences, both in phase and in amplitude, are ob served if the budding index of parent cells and of daughter cells are considered separately. The complex changes of the cell population are clearly demonstrated by the continuous and periodic modification of both cell volume distributions and protein distributions. Ethanol is always accumulated before the drop of dissolved oxygen concentration and one of the peaks of budding index. We propose a model that explains the insurgence of these oscillation as a consequence of changes in cell cycle parameters due to alternate growth in glucose and in ethanol.
The design of controllers for batch bioreactors
Authors: Cardello Ralph J. , San Ka‐Yiu 
Published: December 2004

AbstractThe implementation of control algorithms to batch bioreactors is often complicated by variations in process dynamics that occur during the course of fermentation. Such a wide operating range often renders the performance of fixed gain proportional‐integral‐differential (PID) controllers unsatisfactory. In this work, detailed studies on the control of batch fermentations are per formed. Two simple controller designs are presented with the intent to compensate for changing process dynamics. One design incorporates the concepts of static feedforward‐feedback control. While this technique produces tighter control than feedback alone, it is not as successful as a controller based on gain scheduling. The gain‐scheduling controller, a subclass of adaptive controllers, uses the oxygen uptake rate as an auxiliary variable to fine‐tune the PID controller parameters. The control of oxygen tension in the bioreactor is used as a vehicle to convey the proposed ideas, analyses, and results. Simulation experiments indicate significant improvement in controller performance can be achieved by both of the proposed approaches even in the presence of measurement noise.
Molecular regulation of methanol oxidase activity in continuous cultures of Hansenula polymorpha
Authors: Giuseppin M. L. F. , Van Eijk H. M. J. , Bes B. C. M. 
Published: December 2004

AbstractThe regulation of methanol oxidase (MOX) in Hansenula polymorpha has been studied in continuous cultures using a mixture of glucose and methanol (4:1 w/w) as carbon source. The study focused on the identification of stages in the biosynthesis affecting the formation of active MOX in glucose‐methanol‐grown cells. The levels of MOX mRNA, MOX protein in monomeric and octameric from, the ratio FAD/MOX, and the actual MOX activity have been quantified as functions of the dilution rate D. Hybridization studies with MOX mRNA probes showed an induction of MOX mRNA formation up to D = 0.29 h−1. The induction of MOX protein synthesis (up to 37% of the cellular protein) is determined at low D values on the transcriptional level. The MOX activity at high D values is tuned by FAD incorporation and (post‐) translation. Despite the high levels of MOX mRNA, decreasing levels of MOX activity and MOX protein were found at D values ranging from 0.14 t 0.29 h−1. The maximal ratio FAD/MOX(6) was determined at D = 0.1 h−1, which correlated with the maximal specific activity of MOX. In glucose‐methanol media both protein level and MOX activity are repressed by increasing levels of residual glucose at high D values.
Biospecific adsorption in fixed and periodic countercurrent beds
Authors: Arve B. H. , Liapis A. I. 
Published: December 2004

AbstractA mathematical model that describes the adsorption and wash stages of biospecific adsorption (affinity chromatography) in a packed column is presented. The model expressions account for film and pre diffusion mass transfer as well as for different mechanisms of interaction between the adsorbate(s) and the ligand. The model equations may be applicable to single and multi‐component biospecific adsorption systems involving both monovalent and multivalent adsorbates.The results obtained from model simulations show that the breakthrough time of the adsorbate is significantly influenced by the rate of the interaction step between the adsorbate and the ligand. The results indicate that when short beds are employed, then the choice of ligand with respect to its rate of interaction with the adsorbate may be of paramount importance. In certain systems involving bivalent adsorbates, the adsorbate may be displaced from the one‐site complex, reenter the flowing fluid stream, and increase the effluent adsorbate concentration above its inlet value. It is also shown that when a single column is divided into two beds operating in a periodic counter current mode, the ligand utilization can be almost four times higher than that obtained in a column of the same length operating in the fixed bed mode.The studies on the wash stage indicate that the reduction of the concentration of the contaminant to a specified low level may be accomplished for certain systems in a shorter time, if the direction of flow in the wash stage is opposite to that used in the adsorption stage. However, a larger amount of product will be lost, in general, when the direction of flow of the washing medium is opposite to that employed during the adsorption stage.
Effect of pore size in substrate and diffusion of enzyme on hydrolysis of cellulosic materials with cellulases
Authors: Tanaka Mitsuo , Ikesaka Makoto , Matsuno Ryuichi , Converse Alvin O. 
Published: December 2004

AbstractThe effect of cellulase size on hydrolysis was studied by comparing the behavior of crosslinked cellulase (CC) with normal cellulase (FC). The average molecular weight of the CC was at least three times the molecular weight of the FC. The amounts of each enzyme were adjusted so that the degree of solubilization after 2 h was the same. The degree of solubilization of Avicel with CC was higher than that with FC in the late stage of reaction. The degree of solubilization of pretreated lignocelluloses was much greater than that of Avicel, but the degree of solubilization with CC was lower than that with FC at all times during the reaction. The degree of solubilization of artificial lignified Avicel was higher with FC than with CC, but the degree of solubilization of de‐lignified the artificial lignified Avicel was lower with FC than with CC. The degree of solubilization of amorphous celloulose with FC was the same as that with CC at all times during the reaction. These behaviors are examined by the hypothesis that when small pores dominate, the smaller enzyme components diffuse into the pores and become inactive since synergism with the larger components is no longer possible, whereas, when larger pores dominate, the entire enzyme can diffuse in and therefore the available surface area is increased. This hypothesis is supported by direct measurement of the pore size in two of the substrates and by diffusion inside Avicel of only smaller molecular cellulase component.
Anaerobic digestion of cellulose fraction of domestic refuse by means of rumen microorganisms
Authors: Gijzen H. J. , Zwart K. B. , Teunissen M. J. , Vogels G. D. 
Published: December 2004

AbstractThe anaerobic digestion of a cellulose‐enriched fraction of domestic refuse by means of rumen microorganisms in an “artificial rumen” digester was studied. Various combinations of solid and liquid retention times and loading rates were applied to establish optimum conditions for the acidogenic phase digestion of the refuse fraction. An optimal substrate conversion of about 72% was obtained at a loading rate of 23.4 g volatile solids (VS)/L d and a solids retention time of 90 h. Variation of dilution rate between 1.04 and 3.14 fermentor volume turnovers per day had no effect on degradation efficiency. At a loading rate of 23.4 g VS/L d a differential removal rate of solids and liquids appeared to be necessary to obtain an effective degradation of the refuse fraction.
The enzymatic hydrolysis and fermentation of pretreated wheat straw to ethanol
Authors: Szczodrak Janusz 
Published: December 2004

AbstractAutohydrolysis and ethanol‐alkali pulping were used as pretreatment methods of wheat straw for its subsequent saccharification by Trichoderma reesei cellulase. The basic hydrolysis parameters, i.e., reaction time, pH, temperature, and enzyme and substrate concentration, were optimized to maximize sugar yields from ethanol‐alkali modified straw. Thus, a 93% conversion of 2.5% straw material to sugar syrup containing 73% glucose was reached in 48 h using 40 filter paper units/g hydrolyzed substrate. The pretreated wheat straw was then fermented to ethanol at 43°C in the simultaneous saccharification and fermentation (SSF) process using T. reesei cellulase and Kluyveromyces fragilis cells. From 10% (w/v) of chemically treated straw (dry matter), 2.4% (w/v) ethanol was obtained after 48 h. When the T. reesei cellulase system was supplemented with β‐glucosidase from Aspergillus niger, the ethanol yield in the SSF process increased to 3% (w/v) and the reaction time was shortened to 24 h.
Kinetics and mathematical modeling of homoacetic fermentation of lactate by Clostridium formicoaceticum
Authors: Yang S. T. , Tang I. C. , Okos M. R. 
Published: December 2004

AbstractFermentation kinetics of Clostridium formicoaceticum grown on lactate at pH 7.0 and 35°C was studied. Acetate was the only fermentation product and its production was growth associated. The growth of this bacterium was insensitive to the lactate concentrations studied, but was inhibited by acetic acid. A Monod‐type expression with product inhibition similar to the noncompetitive inhibition of enzyme kinetics was used to model the batch fermentation. An integrated equation was developed and used to help estimating the kinetic parameters in the model. This mathematical model can be used to simulate the homoacetic fermentation of lactate by C. formicoaceticum at pH 7.0 and 35°C.
Large‐scale production of monoclonal antibodies in suspension culture
Authors: Backer M. P. , Metzger L. S. , Slaber P. L. , Nevitt K. L. , Boder G. B. 
Published: December 2004

AbstractMonoclonal antibodies are being manufactured for clinical trials in suspension culture at the 1300‐L scale. Suspension culture offers some advantages relative to high‐density mammalian cell culture methods; in particular, the ability to closely monitor the behavior of cells in a homogeneous environment. Computer control and on‐line mass spectrography of exit gases provide instantaneous information about the culture metabolic activity. Air sparging and agitation by marine impeller provide aeration sufficient to maintain a constant dissolved oxygen tension at cell concentrations up to 5.0 × 106 cells/mL without causing apparent cell damage.
Serial propagation of mammalian cells on gelatin‐coated microcarriers
Authors: Tao Teh‐Yi , Ji Guang‐Yong , Hu Wei‐Shou 
Published: December 2004

AbstractThe ability to serially propagate mammalian cells in microcarrier cultures is essential for large‐scale operation. The success of such serial propagation depends on viable dissociation of cells from microcarriers and the normal growth and product formation after subsequent reinoculation. The high pH treatment developed for dissociating cells from DEAE‐derivatized microcarriers was not as effective for a number of cell strains cultivated on gelatin‐coated microcarriers. By prewashing the cell‐laden microcarriers with buffer containing a chelating agent, bovine kidney cells, BK, human embryonic foreskin fibroblasts, FS‐4, and continuous human kidney cells, TCL‐598 which produces prourokinase, were viably dissociated from commercially available gelatin‐coated microcarriers, Cytodex‐3. Cells dissociated from microcarriers reattached and grew on micro‐carriers subsequent to inoculation into subcultures. However, after subculturing, cells may attach at different rates to newly added beads and to conditioned microcarriers which cells had previously grown. It resulted in an uneven cell distribution on microcarriers and inferior growth kinetics. This effect was more profound for BK and FS‐4 cells which are propagated with a low multiplication ratio. Specifically, BK cells attach to conditioned beads at a faster rate than to new beads, while FS‐4 cells attach to new beads faster than to conditioned beads. Thus, for these two cell strains, a separator was used to separate the microcarriers from the suspension of dissociated cells before subsequent inoculation. For TCL‐598 cells, which are propagated at a high multiplication ratio, this dissociation technique can be applied directly without the separation of dissociated cells and conditioned microcarriers. All the three cell lines tested exhibit normal growth kinetics in serial propagation on microcarriers. Furthermore, the production of prourokinase by TCL598 cells serially propagated on microcarriers was comparable to that inoculated from roller bottles.