bluuebunny/crossref_metadata_2025_split huggingface dataset:
Batch fermentation kinetics of sugar beet molasses by Zymomonas mobilis
Authors: Park S. C. , Baratti J. 
Published: December 2004

AbstractA new osmotolerant mutant strain of Zymomonas mobilis was successfully used for ethanol production from beet molasses. Addition of magnesium sulfate to hydrolyzed molasses allowed repeated growth without the need of yeast extract addition. The kinetics and yields parameters of fermentation on media with different molasses concentrations were calculated. The anabolic parameters (specific growth rate, μ, and biomass yield, YX/S) were inhibited at elevated molasses concentrations while the catabolic parameters (specific ethanol productivity, qp, and ethanol yield, Yp/s) were not significantly affected. In addition to ethanol and substrate inhibition, osmotic pressure effects can explain the observed results.
Estimation of Growth Yield and Maintenance Coefficient of Plant Cell Suspensions
Authors: Schnapp Sherry Rae , Curtis Wayne R. , Bressan Ray A. , Hasegawa Paul M. 
Published: December 2004

AbstractMethodology is presented for the determination of growth yield (Yg) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Yg and m requires measurements of specific growth rate (µ) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Yg and m because µ is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the Km for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the Km, the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Yg and m because various steady‐state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of µ and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.
Solvent effects on biocatalysis in organic systems: Equilibrium position and rates of lipase catalyzed esterification
Authors: Valivety Rao H. , Johnston Grant A. , Suckling Colin J. , Halling Peter J. 
Published: December 2004

AbstractPorcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro‐ and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n‐octanol‐water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.
Immobilization‐stabilization of α‐chymotrypsin by covalent attachment to aldehyde‐agarose gels
Authors: Guisán José M. , Bastida Agatha , Cuesta Carmen , Fernandez‐Lufuente Roberto , Rosell Cristina M. 
Published: December 2004

AbstractWe have developed a strategy for immobilization‐stabilization of α‐chymotrypsin by multipoint covalent attachment of the enzyme, through its amino groups, to agarosealdehyde gels. We have studied the role of the main variables that control the intensity of these enzyme‐support multi‐interaction processes (surface density of aldehyde groups in the activated gel, contact time between the immobilized enzyme and the activated support prior to borohydride reduction of the derivatives, etc.). In this way, we have prepared a number of very different chymotrypsinagarose derivatives. Our best derivatives, with the most intense multipoint attachment, were more stable than one‐point attached derivatives and were more than 60,000‐fold more stable than soluble enzyme in the absence of autolysis phenomena. In spite of the dramatic stabilization, the catalytic activity of these derivatives is little changed (they only lose 35% of intrinsic activity after this intense enzyme‐support multi‐interaction process). In addition, we have also demonstrated the very high capacity of 6% aldehyde‐agarose gels to immobilize pure chymotrypsin (40 mg enzyme/mL catalyst). Furthermore, we have been able to establish a clear correlation between enzyme‐support multipoint covalent attachment, stabilization against very different denaturing agents (heat, urea, organic cosolvents), and insensitivity of those immobilized chymotrypsin molecules to some activating agents.
Continuous glycerolysis of olive oil by Chromobacterium viscosum lipase immobilized in liposome in reversed micelles
Authors: Chang Pahn Shick , Rhee Joon Shick , Kim Jae‐Jin 
Published: December 2004

AbstractChromobacterium viscosum lipase which has adsorbed on liposome and solubilized in microemulsion droplets of glycerol containing a little amount of water could catalyze the glycerolysis of olive oil. Studies on the continuous glycerolysis of olive oil by the immobilized enzyme was done at 37°C in continuous stirred vessel bioreactor with polysulfone membrane. The effect of the flow rate of substrate (olive oil) in isooctane on the conversion and composition of the outlet was investigated using high‐performance liquid chromatography (HPLC). The conversion increased with decrease in the flow rate. And we studied the effect of water content in the glycerol‐water‐lipase solution on the glycerolysis reaction. The conversion to desirable products, mono‐ and di‐olein, was improved without a substantial production of oleic acid at lower water concentrations, i.e., below 8.0% (w/v) which corresponds to a wo value of 0.97. At water concentration higher than 8.0% (w/v), the amount of free fatty acid was dramatically increased. Higher operational stability of the enzyme reactor, and the half‐line of the enzyme continuous reaction was about 7 weeks.
Gas transfer characteristics of a novel membrane bioreactor
Authors: Beeton S. , Millward H. R. , Bellhouse B. J. , Nicholson A. M. , Jenkins N. , Knowles C. J. 
Published: December 2004

AbstractWe show the design features of a membrane bioreactor based on pulsatile flow across dimpled membranes. Results show an enhanced mass transfer of air of at least five‐fold magnitude as compared with flat membranes. An increased working volume form 20 mL to 120 mL reduced the kLA at a given Reynolds number because of axial mixing of fluid from the deoxygenated end chamber. The bioreactor was used to supply air to a hybridoma mammalian cell line, and the calculated oxygen uptake showed that high‐density cultures could be maintained in a 20mL, single‐dimpled cultures could be maintained in a 20 mL, single‐dimpled membrane system. Indirect aeration of a 2 L continuous stirred tank reactor, by a double‐membrane system, showed that air could be supplied to mammalian cells at cell densities of approximately 4 × 106 /mL.
Selective separation and purification of two lipases from chromobacterium viscosum using AOT reversed micelles
Authors: Aires‐Barros M. R. , Cabral J. M. S. 
Published: December 2004

AbstractSelective separation and purification of two lipases form Chromobacterium viscosum were carried out by liquid‐liquid extraction using a reversed micellar system. Optimum parameters for extraction were determined using a 250 mM AOT micellar solution in isooctane. Complete separation of the two lipases was achieved at pH 6.0 with a 50mM potassium phosphate buffer solution containing 50 mM KCI. By adding 2.5% by volume of ethanol to the lipase‐loaded micellar solution, 85% of the extracted lipase could be recovered in a new aqueous phase, 50 mM K2HPO4 with 50 mM KCl, at pH 9.0. Lipase A was purified 2.6‐fold with a recovery of 86%, and lipase B by 1.5‐fold with a recovery of 76%.
Saccharification of steam‐exploded poplar wood
Authors: Excoffier Gérard , Toussaint Bertrand , Vignon Michel R. 
Published: December 2004

AbstractEffects of time, temperature, and pH during the steam explosion of poplar wood were studied with the aim of optimize both pentoses recovery and enzymatic hydrolysis efficiency. Steam explosion of acid impregnated wood chips allowed the recovery of 70% of potential xylose as monomers (217°C, 120 s) Enzymatic hydrolysis of pretreated fiber with Trichoderma reesei CL‐847 cellulase system increased progressively with the severity of the steam treatment conditions. The best yield in term of glucose recovery after 24 h of enzymatic hydrolysis was 70% of potential glucose (225°C, 120 s). Deactivation by adsorption on lignin of Trichoderma reesei cellulases and inhibition of these enzymes by low‐molecular‐weight phenols and trihydroxybutyric acids were noticed.
Xanthan production in bubble column and air‐lift reactors
Authors: Suh Ii‐Soon , Schumpe Adrian , Deckwer Wolf‐Dieter 
Published: December 2004

AbstractA bubble column (0.05 m3) and an air‐lift fermentor (1.2 m3) were used for the production of the exocellular microbial polysaccharide xanthan withXanthomonas campestrisin a synthetic medium. Upon oxygen depletion in the liquid, the xanthan production rate dropped sharply and then became a linear function of the oxygen transfer rate. The volumetric mass transfer coefficients for oxygen conformed to the correlation of Suh et al. Using this correlation in combination with the model for xanthan batch fermentation suggested by Peters et al., the xanthan fermentations in the bubble column were well described. The model also correctly predicted the time course of the molecular weight of the polysaccharide even when a complex medium was used. In the air‐lift fermentor, however, the xanthan production rate and the xanthan yields with respect to oxygen and glucose were lower than expected at the overall oxygen transfer rate. The poor performance of the air lift was traced back to the lack of any oxygen supply in the downcomer.
Effect of feed zone in fed‐batch fermentations of Saccharomyces cerevisiae
Authors: Namdev Pradyumna K. , Thompson B. G. , Gray Murray R. 
Published: December 2004

AbstractIn production‐scale, fed‐batch fermentations, feed is often added to a single point at the top of the fermentor, which, combined with poor mixing, results in formation of a “feed zone” rich in nutrients. Frequent exposure of the culture to high concentrations of nutrients in the feed zone for sufficient duration can produce unexpected effects on its performance. The effect of the feed zone was evaluated by conducting aerobic fed‐batch fermentations of Saccharomyces cerevisiae with both complex and defined media. The broth was recirculated between a recycle loop and a bench‐scale fermentor, and feed was intermittently added into the recycle loop to simulate the circulation of cells through the feed zone. Experiments were carried out for a range of residence times in the recycle loop from 0.5 to 12 min. Biomass yields from the complex‐media fermentations were not affected by exposure to high nutrient levels in the recycle loop for residence times up to 12 min. Ethanol consumption was reduced by as much as 50% for residence time in the loop up to 3 min. Very long exposure of yeast cells to excess nutrient levels (12 min) gave acetic acid formation. In a defined medium, the simulated feed zone effect increased biomass yield by up to 10%, but had no effect on ethanol levels. This study indicates that the feed zone effect on biomass yield in yeast fermentation, using complex substrates, will be negligible under fully aerobic conditions.
Factors affecting microbial sulfate reduction by Desulfovibrio desulfuricans in continuous culture: Limiting nutrients and sulfide concentration
Authors: Okabe S. , Nielsen P. H. , Characklis W. G. 
Published: December 2004

AbstractThe effects of sulfate and nitrogen concentrations of the rate and stoichiometry of microbial sulfate reduction were investigated for Desulfovibrio desulfuricans grown on lactate and sulfate in a chemostat at pH 7.0. Maximum specific growth rates (μmax), half‐saturation coefficients (Ksul), and cell yield (Yc/Lac) of 0.344 ± 0.007 and 0.352 ± 0.003 h −1, 1.8 ± 0.3 and 1.0 ± 0.2 mg/L, and 0.020 ± 0.003 and 0.017 ± 0.003 g cell/g lactate, respectively, were obtained under sulfate‐limiting conditions at 35°C and 43°C. Maintenance energy requirements for D. desulfuricans were significant under sulfate‐limiting conditions. The extent of extracellular polymeric substance (EPS) produced was related to the carbon: nitrogen ratio in the medium. EPS production rate increased with decreased nitrogen loading rate. Nitrogen starvation also resulted in decreased cell size of D. desulfuricans. The limiting C : N ratio (w/w) for D. desulfuricans was in the range of 45 : 1 to 120 : 1. Effects of sulfide on microbial sulfate reduction, cell size, and biomass production were also ivestigated at pH 7.0. Fifty percent inhibition of lactate utilization occurred at a total sulfide concentration of approximately 500 mg/L. The cell size of D. desulfuricans decreased with increasing total sulfide concentration. Sulfide inhibition of D. desulfuricans was observed to be a reversible process. © 1992 John Wiley & Sons, Inc.
Enhancement effect of water activity on enzymatic synthesis of cephalexin
Authors: Hyun Chang K. , Kim Jung H. , Ryu Dewey D. Y. 
Published: December 2004

AbstractThe effect of water activity (aw) of the reaction medium on the enzymatic synthesis of cephalexin (CEX) from 7‐amino‐3‐deacetoxycephalosporanic acid (7‐ADCA) and D‐α‐phenylglycine methyl ester (PGM) was investigated using the α‐amino acid ester hydrolase enzyme from Xanthomonas citri. It was found that the synthetic activity of the enzyme and the conversion yield were markedly improved when the aw of the reaction medium was lowered to about 0.97. The water activity depressing agents evaluated were glycerol, sucrose, and sorbitol, and the conversion yields were improved up to 170% with 15% glycerol, 230% with 30% sucrose, and 270% with 20% sorbitol, respectively. The extent of favorable effect of aw on the conversion yield was not the same among the aw depressors, probably due to other unknown interactions between the enzyme and depressors. However, optimal aw values corresponding to the maximum conversion yield coincided for all aw depressors used. The conversion yield of CEX showed an increasing trend with increasing aw up to the optimal aw value (0.96–0.97) which corresponds to the maximum conversion yield and a decreasing trend beyond the optimal aw. There appears to be a delicate balance between the hydrolytic reaction of PGM and synthetic reaction of CEX. The increasing aw–[E · PGM] complex and the branched reaction pathway fluxes from [E · PGM] to PG (D‐α‐phenyl glycine) and CEX are balanced in such a way that the maximum CEX conversion yield is obtained at aw value of 0.96–0.97. The aw depressors stabilized the enzyme somewhat, but this positive effect was considered to be only a minor contribution to the substantial yield enhancement. The aw depressor effect on viscosity and in turn the mass transfer rate limitation was ruled out since the change in conversion due to the viscosity change was found to be insignificant. © 1993 John Wiley & Sons, Inc.
Numerical and Monte Carlo simulations of phenolic polymerizations catalyzed by peroxidase
Authors: Ryu Keungarp , McEldoon James P. , Pokora Alexander R. , Cyrus William , Dordick Jonathan S. 
Published: December 2004

AbstractNumerical and Monte Carlo simulations of horseradish peroxidase–catalyzed phenolic polymerizations have been performed. Kinetic constants for the simulations were fit to data from the oxidation and polymerization of bisphenol A. Simulations of peroxidase‐catalyzed phenolic polymerization were run as a function of enzyme concentration and radical transfer and radical coupling rate constants. Predictions were performed with respect to conversion vs. time and number average molecular weight and polydispersity vs. conversion. It is shown that the enzymatic polymerization of phenols can be optimized with respect to high molecular weights by employing low enzyme concentrations and phenols with low radical coupling rate constants coupled with relatively high radical transfer rate constants. Such phenols may be identified by using linear free energy relationships that relate radical reactivity to electron donating/withdrawing potential of the phenolic substituent. © 1993 John Wiley & Sons, Inc.
A numerical analysis of forces exerted by laminar flow on spreading cells in a parallel plate flow chamber assay
Authors: Olivier Lauri A. , Truskey George A. 
Published: December 2004

AbstractExposure of spreading anchorage‐dependent cells to laminar flow is a common technique to measure the strength of cell adhesion. Since cells protrude into the flow stream, the force exerted by the fluid on the cells is a function of cell shape. To assess the relationship between cell shape and the hydrodynamic force on adherent cells, we obtained numerical solutions of the velocity and stress fields around bovine aortic endothelial cells during various stages of spreading and calculated the force required to detach the cells. Morphometric parameters were obtained from light and scanning electron microscopy measurements. Cells were assumed to have a constant volume, but the surface area increased during spreading until the membrane was stretched taut. Two‐dimensional models of steady flow were generated using the software packages ANSYS (mesh generation) and FIDAP (problem solution). The validity of the numerical results was tested by comparison with published results for a semicircle in contact with the surface. The drag force and torque were greatest for round cells making initial contact with the surface. During spreading, the drag force and torque declined by factors of 2 and 20, respectively. The calculated forces and moments were used in adhesion models to predict the wall shear stress at which the cells detached. Based upon published values for the bond force and receptor number, round cells should detach at shear stresses between 2.5 and 6 dyn/cm2, whereas substantially higher stresses are needed to detach spreading and fully spread cells. Results from the simulations indicate that (1) the drag force varies little with cell shape whereas the torque is very sensitive to cell shape, and (2) the increase in the strength of adhesion during spreading is due to increased contact area and receptor densities within the contact area. © 1993 John Wiley & Sons, Inc.
Molecular integrity of monoclonal antibodies produced by hybridoma cells in batch culture and in continuous‐flow culture with integrated product recovery
Authors: Mohan S. B. , Chohan S. R. , Eade J. , Lyddiatt A. 
Published: December 2004

AbstractThe molecular integrity of monoclonal antibodies (MCAB) produced by murine hybridoma cell line TB/C3 was studied in batch and continuous‐flow cultures. In batch culture, one band of MCAB was detected initially by Western blotting of sodium dodecyl sulfate (SDS)–polyacrylamide gels run under unreduced conditions, but heterogenous MCAB bands appeared as the culture aged. The latter were due to the degradation of MCAB by proteases active at the neutral pH of the culture. The deleterious effect of proteases was minimized in the continuous‐flow cultures which were integrated for product recovery. The MCAB of high quality was purified over 26 days from a culture grown at a dilution rate of 0.025 h−1 (experiment 1). However, at a lower dilution rate of 0.015 h−1 (experiment 2), the integrity of MCAB was compromised after the initial 13 days of culture. This was shown to be due to the variation in the carbohydrate content of MCAB produced, as judged by the increased sialylation of heavy chains and the varied reactivity of MCAB with lectins (Maackia amurensis agglutinin, Galanthus nivalis agglutinin, and Datura stramonium agglutinin) as the age of the culture increased. The concentration of the purified MCAB samples by enzyme‐linked immunosorbent assay (ELISA) (used normally) was usually higher than that estimated by absorbance at 280 nm. Best correlation between the two methods (ELISA–280 nm ratio of 1.02–1.25) was obtained with experiment 1 samples. This ratio increased in experiment 2 and batch culture samples as the heterogeneity of MCAB produced increased, being 1.03–2.94 and 2.53–4.62, respectively. Therefore, ELISA overestimated MCAB concentration when the molecular integrity of the latter was compromised. The ELISA–A280 nm ratio might hence provide a useful indicator for assessing the quality of MCAB produced. Comparison of SDS–polyacrylamide gels stained with Coomassie Brilliant Blue R and silver showed that the former correlated better with the MCAB activity stain, whereas the silver stained both the protein‐ and carbohydrate‐rich components. Comparison of the patterns produced with these two stains might therefore offer another parameter to monitor the overall integrity of MCAB produced. Finally, the data presented have important implications on the validity of using long‐term and intensive cultures for generating MCAB because such cultures would be subjected to the additive effects reported for batch and continuous modes of growth. © 1993 John Wiley & Sons, Inc.
Surfactant‐Induced hydrogen production in cyanobacteria
Authors: Famiglietti M. , Hochkoeppler A. , Luisi P. L. 
Published: December 2004

AbstractAddition of Tween 85 to aqueous suspensions of Anabaena variabilis induced photosynthetic evolution of hydrogen over a time span of several weeks: As much as 148 nmol H2/h · mg dry weight was produced in the first week by a suspension containing 4.2 mg dry weight of cells and 77 mM Tween 85. The chemical structure of Tween 85 was a necessary prerequisite for inducing hydrogen production, as compounds such as Tween 20, 60, and 80 had a quite different effect. There was a coupling between photosynthetic oxygen evolution and hydrogen evolution: Hydrogen evolution started to be effective only when oxygen evolution subdued. The presence of heterocysts in A. variabilis was also required for the Tween‐induced hydrogen production. Based on these observations, possible mechanisms for the photosynthetic effect of Tween 85 are advanced and discussed. © 1993 John Wiley & Sons, Inc.