bluuebunny/crossref_metadata_2025_split huggingface dataset:
A kinetic expression for hydrolysis of soluble starch by glucoamylase
Authors: Kusunoki Koichiro , Kawakami Koei , Shiraishi Fumihide , Kato Keiichi , Kai Mayumi 
Published: December 2004

AbstractAs the hydrolysis of starch by glucoamylase proceeds with stepwise removal of glucose units from the nonreducing ends of the starch chain, the number of available substrate molecules is essentially unchanged in the course of the degradation. In view of this aspect, a simple practical kinetic expression, which consists of a modified Michaelis–Menten form with product inhibition, is presented for the hydrolysis of soluble starch. It is assumed that the values of kinetic parameters Vm and Km vary linearly from the values for starch toward those for maltose. The applicability of this kinetic expression is verified through the simulation with the experimental results for the hydrolysis of two soluble starches with different average molecular weights of 3 × 104 and 3 × 106.
Enhancement of starch conversion efficiency with free and immobilized pullulanase and α‐1,4‐glucosidase
Authors: Ram Kumar A. , Venkatasubramanian K. 
Published: December 2004

AbstractGlucoamylase and pullulanase were immobilized on reconstituted bovine‐hide collagen membranes using the covalent azide linkage method. A pretanning step was incorporated into the immobilization procedure to enable the support matrix to resist proteolytic activity while accommodating an operating temperature of 50°C. The immobilized glucoamylase and pullulanase activities were 0.91 and 0.022 mg dextrose equivalent (DE) min−1 cm−2 of membrane, respectively. Immobilized glucoamylase had a half‐life of 50 days while the immobilized pullulanase had a half‐life of 7 days. This is a considerably improved stability over that reported by other researchers. The enzymes were studied in their free and immobilized forms on a variety of starch substrates including waxy maize, a material which contains 80% α‐1–6‐glucosidic linkages. Substrate concentrations ranged from 1% to a typical commercial concentration of 30%. Conversion efficiencies of 90–92% DE were obtained with free and immobilized glucoamylase preparations. Conversion enhancements of 4–5 mg of DE above this level were obtained by the use of pullulanase in its free or immobilized forms. Close examination of free pullulanase stability as a function of pH indicated improved thermal stability at higher pH values. At 50°C and pH 5.0, the free enzyme was inactivated after 24 h. At pH 7.0, the enzyme still possessed one‐half its activity after 72 h. Studies were conducted in both batch and continuous total recycle reactors. All experiments were conducted at 50°C. Experiments conducted with coimmobilized enzymes proved quite promising. Levels of conversion equivalent to those obtained with the individually immobilized enzymes were realized.
The mechanism of uranium biosorption by Rhizopus arrhizus
Authors: Tsezos M. , Volesky B. 
Published: December 2004

AbstractBiosorption of elements is a little understood phenomenon exhibited by some types of even nonliving microbial biomass. A common fungus Rhizopus arrhizus has been reported to take up uranium from aqueous solutions to the extent of 180 mg U6+/g. The mechanism of uranium sequestering by this type of biomass was studied by using experimental techniques such as electron microscopy, x‐ray energy dispersion analysis, IR spectroscopy, and supporting evidence was obtained for a biosorption mechanism consisting of at least three processes. Uranium coordination and adsorption in the cell‐wall chitin structure occur simultaneously and rapidly whereas precipitation of uranylhydroxide within the chitin microcrystalline cell‐wall structure takes place at a lower rate. Interference of Fe2+ and Zn2+ coions with uranium biosorption is indicated.
Oxygen mass transfer into aerated CMC solutions in a bubble column
Authors: Deckwer W.‐D. , Nguyen‐Tien K. , Schumpe A. , Serpemen Y. 
Published: December 2004

AbstractDiffering findings on the volumetric mass transfer coefficients kLa in CMC solutions in bubble column bioreactors have been reported in the literature. Therefore, oxygen mass transfer was studied again in CMC solutions in a 14‐cm‐i.d. × 270‐cm‐height bubble column using different spargers. The kLa values were determined along with the dispersion coefficients by fitting the prediction of the axial dispersed plug model with the experimental oxygen concentration profiles in the liquid phase. Surprisingly, the obtained liquid phase dispersion coefficients for CMC solution are higher than one would expect from correlations. The kLa data depend largely on the flow regime. In general, they are lower than those reported in the literature. The data for developing slug and established slug flow are dependent on the gas velocity and the effective viscosity of the solution and can br correlated by a simple correlation. This correlation describes kLa values measured on fermentation broth of Penicillium chrysogenum with striking agreement.
Recycle in fermentation processes
Authors: Hamer G. 
Published: December 2004

AbstractUntil recently, the recycle of the solid (microbial), liquid, or gaseous phases in microbiological processes has only been practiced rarely, with the notable exception of activated sludge processes for wastewater treatment, where recycling of a large fraction of the microbial phase is essential for process stability and performance. During the last decade, the economic impact of a number of politically motivated changes with respect to energy and feedstock costs and availability, and legislation directed towards markedly higher levels of environmental protection have encouraged the evaluation and subsequent development of recycle technology in the fermentation industry. Many of the developments have occurred in isolation and some have failed to result in either an improvement in process economics or any reduction in the quantity of pollutants discharged. This article seeks to review the present diversity of approaches to recycle technology in fermentation processes in order to provide a sensible basis for future developments.
Hydrodynamic stress capacity of microorganisms
Authors: Bronnenmeier R. , Märkl H. 
Published: December 2004

AbstractA new experimental method has been developed for estimating the hydrodynamic stress capacity of microorganisms. In a test apparatus, stable continuous cultures of three types of green algae and two cyanobacteria were exposed to well‐defined hydrodynamic loads in a free jet. During and after the stress experiments the cultures showed a different response due to the damage in the jet. The results of these free‐jet experiments with short stress exposure were compared to those of stirring experiments in which hydrodynamic load was continuously generated by a stirrer. In both kinds of experiments distinct critical stress values could be determined below which no essential damage of the microorganisms cultures occurred. A correlation between the critical stress values in free‐jet and stirring experiments was found. It can be deduced that the free‐jet data, expressed as critical volumetric dissipated energy, are suitable for the calculation of hydrodynamic stress to which microorganisms might be exposed in biotechnical plants without suffering damage.
Carbon limitation of biomass production in high‐rate oxidation ponds
Authors: Azov Y. , Shelef G. , Moraine R. 
Published: December 2004

AbstractTheoretical considerations confirmed by outdoor experiments indicated carbon limitation of biomass production in high‐rate oxidation ponds at certain seasonal and operational conditions. Apparently, free carbon dioxide concentration in the pond is the major determinant of carbonlimiting algal photosynthesis. High concentrations of free CO2 are provided through bacterial respiration which is the main contributor to algal photosynthesis. At high photosynthetic activities and low organic loadings, free CO2 concentrations are low; its flux into algal cells determines photosynthesis and biomass production rate in the pond.
Film diffusional influences on the kinetic parameters in packed‐bed immobilized enzyme reactors
Authors: Patwardhan V. S. , Karanth N. G. 
Published: December 2004

AbstractA number of studies on packed‐bed immobilized enzyme reactors have shown the significant influence of the external film mass transfer resistance on the apparent kinetic parameters. Some of the earlier mathematical models using approximation techniques have attempted to explain the linearity of the S0x vs ln (1 − x) plots observed experimentally for systems obeying Michaelis–Menten kinetics. However, there has been no critical examination of the bounds of validity of the approximations used. Further, the situations where the above linearity is not valid have been examined neither conceptually nor quantitatively. The work presented here overcomes these drawbacks of the earlier analyses by approaching the problem from a different angle. Methods of evaluation of the intrinsic kinetic parameters under different experimental situations have been outlined and illustrated with several examples.
Accumulation of heavy metals in unicellular algae
Authors: Khummongkol D. , Canterford G. S. , Fryer C. 
Published: December 2004

AbstractA model for metal uptake by microorganisms based on surface adsorption has been developed, and then applied to the uptake of cadmium by Chlorella vulgaris. A linear equilibrium relationship between metal in the solution and that adsorbed on the cell surface is assumed and confirmed at low cadmium concentrations by short‐term uptake experiments. When it incorporates a description of cell growth, the model predicts an initial rapid uptake and a subsequent slow uptake. Such behavior has often been observed in experiments with growing microorganisms. This indicates that the slow uptake, sometimes thought to be active or metabolic, could be due to the simultaneous effects of growth and surface adsorption. The model shows that initial metal uptake is fast and approaches equilibrium within a few seconds. This prediction is in agreement with experimental results in a batch system: Equilibrium is reached before the first samples are taken (at 10 min) and there is then no measurable change until growth provides a significant increase in cell surface (after several hours). Thus the equilibrium constant can be calculated from experimental results of uptake at 10 min. The equilibrium is found to be affected by phosphate concentration; the amount of cadmium adsorbed on the cell decreases as the concentration of phosphate is increased. Long‐term uptake experiments in growing cultures show a greater metal accumulation than predicted by the adsorption model, suggesting the involvement in the slow long‐term uptake of some mechanism other than adsorption. This is confirmed by experiments in which uptake in cultures exposed to cadmium throughout the growth period is compared with short‐term uptake in similar cultures grown in the absence of cadmium. The modeling approach to metal adsorption provides a basis for further development. A model combining description of adsorption and of intracellular accumulation is necessary to provide a more complete description. Such a model, with precise definitions of system parameters and means of evaluating these parameters from experimental results, will be a powerful tool in investigation of metal uptake by microorganisms.
Diffusion and the limiting substrate in two‐substrate immobilized enzyme systems
Authors: Leypoldt John K. , Gough David A. 
Published: December 2004

AbstractThe effects of mass transport resistances on two‐substrate immobilized enzyme systems are investigated theoretically. It is shown that the effects of mass transport resistances on the overall reaction rate are related mainly to the transport of the limiting substrate. In the absence of external mass transport resistances, the limiting substrate can be identified by knowing only the ratio of the bulk substrate concentrations, the permeability of the support to the two substrates, and the stoichiometry of the reaction. However, a combination of internal and external mass transport resistances may result in the other substrate becoming limiting. These effects are most significant when the mass transport resistances are high. Applications in the design of enzyme electrodes and chemical reactors are discussed.
Preparation and properties of fibrinolytic enzymes produced by Cochliobolus lunatus
Authors: Abdel‐Fattah Ahmed F. , Ismail Abdel Mohsen S. 
Published: December 2004

AbstractSome properties of the crude lyophilized fibrinolytic enzyme produced by Cochliobolus lunatus in surface culture were studied. Enzyme concentrations over the range from 0.16 to 10.16 mg/mL showed that concentration above a certain level ceased to be the limiting factor controlling enzyme action. At pH 6.8 and a temperature of 40°C, the fibrinolytic enzyme showed maximal activity at a human fibrin concentration of 2 mg/mL. The optimum pH values for enzyme activity were 6.98 and 7.0, using Sørensen and Mcllvaine buffers, respectively. Fibrinolytic enzymes were isolated from a static culture of Cochliobolus lunatus; isolation was carried out with various agents. Ammonium sulphate yielded the highest recovered fibrinolytic activity. The fraction salted out by precipitation at 25% ammonium sulphate saturation possessed the highest recovered fibrinolytic activity compared to the ammonium sulphate, ethanol, and acetone fractions.
Effect of dissolved oxygen on nitrogen fixation by A. vinelandii. I. Free cell cultures
Authors: DiLuccio Robert C. , Kirwan Donald J. 
Published: December 2004

AbstractAs part of an investigation into the use of biological nitrogen fixation for fertilizer ammonia production, continuous culture studies of respiration and nitrogen fixation in the aerobic bacteria Azotobacter vinelandii under oxygen‐limited conditions were conducted. Respiration and growth rates followed Monod forms with respect to dissolved oxygen concentration. However, specific nitrogen fixation rate and nitrogenase activity exhibited maximum values at dissolved oxygen concentrations of ca. 0.02 mM (10% of air saturation). These results suggest careful control of oxygen in the environment is necessary to optimize fixed nitrogen production by this organism.
Environmental parameters influencing phenolics production by batch cultures of Nicotiana tabacum
Authors: Sahai O. P. , Shuler M. L. 
Published: December 2004

AbstractThe influence of temperature, illumination, hormonal levels (2,4‐D and kinetin), carbon to nitrogen ratios, antibiotics, and precursor feeding on phenolics production by Nicotiana tabacum (tobacco) was studied. This plant cell system was chosen as a model system to learn more about secondary product formation in plant cell tissue cultures. This is the first study to manipulate all of these environmental parameters with a single plant cell system. The most striking results were with 2,4‐D manipulation. The removal of 2,4‐D resulted in significant phenolics production during the stationary phase, while normal levels strongly suppressed phenolics production during the stationary phase. The addition of phenylalanine stimulated phenolics production per gram of cells but strongly inhibited growth.
Practical reactor systems for yeast cell immobilization using biomass support particles
Authors: Black G. M. , Webb C. , Matthews T. M. , Atkinson B. 
Published: December 2004

AbstractThe technique of cell immobilization using porous support particles (biomass support particles) has been successfully applied to yeast cells. Two reactor configurations exploiting the use of these particles have been developed and assessed for use in aseptic yeast fermentations. A liquid‐fluidized bed fermenter has been devised for use with particles denser than the fermentation liquor whilst a gas‐stirred circulating bed fermenter proved suitable for particles of essentially neutral buoyancy. Both systems have been operated successfully for extended periods of continuous operation. The utilization of biomass support particle technology in such reactors provides a practical and robust system for immobilized cell reactors. This technology offers significant opportunities for further development.
Butanediol production by Aerobacter aerogenes NRRL B199: Effects of initial substrate concentration and aeration agitation
Authors: Sablayrolles J. M. , Goma G. 
Published: December 2004

AbstractButanediol production by Aerobacter aerogenes NRRL B199 grown on glucose requires an optimal rate of aeration for the obtention of butanediol 2, 3. In the absence of air, Aerobacter aerogenes NRRL B199 growth and production are weak. Agitation‐aeration is necessary for producing the biomass, but an excess of oxygen proves to be toxic with regard to metabolite production. Oxygen is a limiting substrate with regard to growth and an inhibitor with regard to the specific metabolite productivity. This observation is discussed from a kinetic stand point and in relation to the search for the optimum oxygen transfer coefficient (KLa), which is found to be in the range of 50–100h−1. It has also been observed that KLa increases during the fermentation cycle. The initial substrate concentration effects the yield production of biomass and butanediol production. Low yields of butanediol are obtained at low initial sugar concentrations, but good yields of butanediol are obtained (0.45 g/g) at high concentrations of glucose (195 g/L). Carbon substrates and butanediol are inhibitors of cell growth while butanediol is not quite an inhibitor of the specific rate of butanediol production for the range of butanediol of 0–100 g/L.
Computer model for glucose‐limited growth of a single cell of Escherichia coli B/r‐A
Authors: Domach M. M. , Leung S. K. , Cahn R. E. , Cocks G. G. , Shuler M. L. 
Published: December 2004

AbstractA computer model is described which is capable of predicting changes in cell composition, cell size, cell shape, and the timing of chromosome synthesis in response to changes in external glucose limitation. The model is constructed primarily from information on unrestricted growth in glucose minimal medium. The ability of the model to make reasonable quantitative predictions under glucose‐limitation is a test of the plausibility of the basic biochemical mechanisms included in the model. Such a model should be of use in differentiating among competing hypotheses for biological mechanisms and in suggesting as yet unobserved phenomena. The last two points are illustrated with the testing of a mechanism for the control of the initiation of DNA synthesis and predictions on cellwidth variations during the division cycle.
Increased digestibility of bagasses by pretreatment with alkalis and steam explosion
Authors: Playne M. J. 
Published: December 2004

AbstractAlkali treatment and steam explosion of bagasse were investigated in order to develop economical and effective methods of increasing the digestibility of bagasse. The treated bagasse was to be used as a substrate for the production of volatile fatty acids by anaerobic acidogenic bacteria. The alkalis examined were NaOH, NH3 (aqueous), NaOH + NH3, Ca(OH)2, and Ca(OH)2 + Na2CO3, at ambient temperature and in combination with steam explosion at 200°C, 6.9 MPa, and 5 min cooking times. Digestibilities of up to 733 g organic matter (OM)/kg bagasse dry matter (DM) were obtained for bagasse treated with NaOH and Ca(OH)2 + Na2CO3; less than 430 g OM was obtained for bagasse treated with aqueous NH3; and up to 724 g OM was obtained for bagasse treated with Ca(OH)2. This digestibility was only achieved by using high concentrations of Ca(OH)2, i.e., 180–300 g/kg bagasse. Steam explosion increased the digestibility of bagasse up to 740 g OM in the presence of alkali but only to 610 g OM in the absence of alkali. The digestibility of bagasse without pretreatment was 190 g OM/kg bagasse DM. More than one‐half the hemicellulose present was solubilized by pretreatment. The composition of the liquid fraction of steam‐exploded material was examined and contained mainly xylose monomers and oligomers (112 g/kg original bagasse DM) and acetic acid (33 g/kg original DM). The relative costs of the alkalis used were obtained for the United States, Australia, and Europe. Lime [Ca(OH)2] was the least expensive alkali per unit of additional digestible OM obtained. Ammonia was the most expensive alkali to use, except in the United States where the difference in its cost relative to other alkalis was smaller. However, ammonia provides organic nitrogen for microbial growth, and could be recycled. With acidogenic fermentations, alkali is able to double as a neutralizing agent during fermentation. Thus, concentrations of alkali equal to that required for neutralization may be used in pretreatment. Concentrations of Ca(OH)2 as high as 300 g/kg bagasse were needed for neutralization and should, therefore, be considered for pretreatment. Steam explosion of bagasse resulted in digestible, sterilized substrates of small particle size with readily separable liquid and pulp streams.
Thermodynamics of water and ethanol adsorption on four starches as model biomass separation systems
Authors: Rebar V. , Fischbach E. R. , Apostolopoulos D. , Kokini J. L. 
Published: December 2004

AbstractAdsorption of water and ethanol on four starches has been studied in the temperature range of 50–90°C. The results show that adsorption of water on starch‐based materials is enhanced when the amount of amylopectin is highest. Adsorption of ethanol is not significantly affected by the kind of starch used. Heats of adsorption calculated from retention data are in the range from −9.3 to −13.7 kcal/g mol for water and −5.6 to −6.76 kcal/g mol for ethanol. Calculated free energies of adsorption suggest that adsorption is most spontaneous at lower temperatures as expected.
Continuous enzymatic cooking and liquefaction of starch using the technique of direct resistive heating
Authors: Varella V. L. , Concone B. R. V. , Senise J. T. , Doin P. A. 
Published: December 2004

AbstractContinuous cooker prototypes of very simple design, using electricity as a primary energy source, were developed for the process of cooking and liquefaction of starch suspensions. Previous work on equipment using microwave dielectric heating has already been reported. Results of energy consumption as low as 330 kcal/kg based on starch content were achieved. Considering these results and looking for new solutions or engineering concepts, the authors have been investigating the possibility of using electric energy at 60 Hz for direct resistive heating, in which the starch suspension is the proper “resistor.”The most important results of energetic yield obtained until now, working in a continuous process of cooking–liquefaction, are not larger than 235 kcal (272 Wh)/kg based on starch content. These results were obtained using a commercial grade α‐amylase from B. subtillis, working with temperatures ranging from 70 to 75°C, and with residence times in the reactor not greater than 1.5 min. The experiments of saccharification and fermentation accomplished as a test for the efficiency of this heating technique gave good results (as with a conventional technique) and thus enabled us to proceed with the studies.
Characterization of algae using regularities
Authors: Lee H. Y. , Erickson L. E. 
Published: December 2004

AbstractThe weight fraction carbon and reductance degree of algae are reviewed for literature data. Average values are compared with values for yeast and bacteria. The results show that the standard deviation and coefficient of variation are small as long as the algae are grown under adequate nutritional conditions. For nitrogen‐deficient growth conditions, the storage of lipids has been observed; this results in values of weight fraction carbon and reductance degree which are larger than the average values.