bluuebunny/crossref_metadata_2025 huggingface dataset:
The conformational analysis of peptides using fourier transform IR spectroscopy
Authors: Haris Parvez I. , Chapman Dennis
Published: December 2004

Fourier transform infrared spectroscopy (FTIR) can be used for conformational analysis of peptides in a wide range of environments. Measurements can be performed in aqueous solution, organic solvents, detergent micelles as well as in phospholipid membranes. Information on the secondary structure of peptides can be derived from the analysis of the strong amide I band. Orientation of secondary structural elements within a lipid bilayer matrix can be determined by means of polarized attenuated total reflectance–FTIR spectroscopy. Hydrogen–deuterium exchange can be monitored by the analysis of the, amide II band. This review gives some example of peptide systems studied by FTIR spectroscopy. Studies on alamethicin and α‐aminoisobutyric acid containing peptides have shown that FTIR spectroscopy is a sensitive tool for identifying 310‐helical structures. Changes in the structure of the magainins upon interaction with charged lipids were detected using FTIR spectroscopy. Tachyplesin is an example of a β‐sheet containing membrane active peptide. Polarized ir spectroscopy reveals that the antiparallel β‐sheet structures of tachyplesin are oriented parallel to the membrane surface. Synthesis of peptides corresponding to functionally/structurally important regions of large proteins is becoming increasingly popular. FTIR spectroscopy has been used to analyze the structure of synthetic peptides corresponding to the ion‐selective pore of the voltage‐gated potassium channel. In biomembrane systems these peptides adopt a highly helical structure. Under conditions, where these peptides are aggregated the presence of some intermolecular β‐sheet structure can also be detected. © 1994 John Wiley & Sons, Inc.
A model for enzymatic isomerization of D‐glucose to D‐fructose in a batch reactor
Authors: Sproull Robert D. , Lim Henry C. , Schneider Daniel R.
Published: December 2004

Using whole cells containing glucose isomerase, mathematical models for the enzymatic conversion of D‐glucose to D‐fructose and for the inactivation of the enzyme catalyst have been postulated and verified experimentally. The heat of reaction, the equilibrium constant, and the individual rate constants and their activation energies have been estimated. The model can be used to predict the time course for the enzymatic production of fructose in a batch reactor within the tested experimental range of 40–80°C.
The production of foot‐and‐mouth disease virus from BHK 21 C 13 cells grown on the surface of glass spheres
Authors: Spier R. E. , Whiteside J. P.
Published: December 2004

In view of the advantages which are associated with the use of the BHK monolayer cell for the production of foot‐and‐mouth disease (FMD) virus, a unit system using glass spheres was developed to grow BHK monolayer cells and to test the susceptibility of such cells to FMD virus. The yield of cells and their susceptibility compares favorably with BHK monolayer cells which have been grown in Roux bottles.
The production of foot‐and‐mouth disease virus from BHK 21 C 13 cells grown on the surface of DEAE sephadex A50 beads
Authors: Spier R. E. , Whiteside J. P.
Published: December 2004

Methods are described which make possible the production of foot‐and‐mouth disease (FMD) virus from BHK 21 C13 monolayer cells which have been grown on the surface of serum coated DEAE Sephadex A50 beads. The yield of cells and their susceptibility to infection by FMD virus are equivalent to conventional Roux monolayer systems. The potential for the commercial application of the DEAE Sephadex A50 system is discussed in relation to other unit process monolayer systems and in particular to the system in which cells are cultured in a deep bed of small glass spheres.
Effects of immobilization on the kinetics of enzyme‐catalyzed reactions. I. Glucose oxidase in a recirculation reactor system
Authors: Ramachandran K. B. , Perlmutter D. D.
Published: December 2004

Glucose oxidase from Aspergillus niger was immobilized on nonporous glass beads by covalent bonding and its kinetics were studied in a packed‐column recycle reactor. The optimum pH of the immobilized enzyme was the same as that of soluble enzyme; however, immobilized glucose oxidase showed a sharper pH‐activity profile than that of the soluble enzyme. The kinetic behavior of immobilized glucose oxidase at optimum pH and 25°C was similar to that of the soluble enzyme, but the immobilized material showed increased temperature sensitivity. Immobilized glucose oxidase showed no loss in activity on storage at 4°C for nearly ten weeks. On continuous use for 60 hr, the immobilized enzyme showed about a 40% loss in activity but no change in the kinetic constant.
Time delay in simple chemostat models
Authors: Macdonald N.
Published: December 2004

The models of Monod and Williams, for the growth of unicellular organisms in chemostats, give strongly damped transients in the biomass and cell number when the flow rate of the chemostat is changed. A simple trick is used to incorporate time delay in these models while still allowing a conventional stability analysis. For long enough time delays the equilibrium point is unstable and limit cycles can be computed. Results obtained using Williams' model, with weakly damped transients as a result of using moderately long time delay, are compared with his data in which cell numbers show weak damping but biomass shows strong damping.
Pilot scale exponential growth of Escherichia coli W to high cell concentration with temperature variation
Authors: Bauer S. , White M. D.
Published: December 2004

An efficient method to grow Escherichia coli W to high cell concentrations on the pilot scale is described and discussed. The method involves growth linked introduction of glucose; and ammonia to the culture, sparing with oxygen, and maintenance of aerobic conditions by gradually decreasing the temperature in the culture in order to keep the oxygen demand within the limits of the capacity of supply. Under these conditions the linear rate of cell mass production is actually the result of exponential growth with a gradually decreasing growth‐rate constant.

About 10 kg packed cells were produced in a 50 liter working‐volume fermentor in one run of 13 hr. The concentration of the cells at the end of the growth was about 47 g dry cells/liter. The expenditure for nutrients was minimal and the controls were of simple automatic nature. From the determined yield constants for glucose, nitrogen, phosphorus, and oxygen it may be inferred that the cells grown by this method are similar to those grown exponentially at constant temperature.
Optimal control of a semibatch fermentation
Authors: Ohno Hiromu , Nakanishi Eiji , Takamatsu Takeichiro
Published: December 2004

This work is concerned with the optimization study of the semibatch fermentation by which an amino acid is produced. The particular fermentation studied is the synthesis of lysine by the auxotrophic mutant. Applying Green's theorem to the maximization problem was proposed, and it succeeded in determining the feed rate of the substrate that maximized the production rate of the desired product.
Biosynthesis of flavors by Penicillium roqueforti
Authors: Kinsella John E. , Hwang Dan
Published: December 2004

The development of the unique flavor of blue type cheese depends on the concerted action of numerous enzymes of Penicillium roqueforti involved in protein and lipid metabolism. Protease(s) by degrading casein modify the texture and background flavor of the ripening cheese. Lipase by hydrolyzing milk triglycerides provides flavorful fatty acids and precursors of methyl ketones. The enzyme complex involved in the partial oxidation of free fatty acids and the properties of β‐ketoacyl decarboxylase which generates the major flavor components of blue cheese are discussed. Fermentation of P. roqueforti for the rapid production of methyl ketones is briefly reviewed.
The chemistry of some microbially induced flavor defects in milk and dairy foods
Authors: Morgan M. E.
Published: December 2004

The “malty” flavor defect that commonly develops in raw milk produced in certain areas of North America and Europe has long been known to be due to the metabolic activity of Streptococcus lactis var. maltigenes. The identification of the aldehydes and alcohols responsible for this flavor defect and the mechanisms involved in their formation from amino acids are discussed.

Pseudomonas fragi, a common psychrophilic recontaminant, is responsible for development of “fruity” flavors in processed dairy products by virtue of the organisms ability to hydrolyze milk fat and esterify certain of the lower fatty acids with ethanol. A similar esterase is present in certain lactic cultures used in the manufacture of cheddar cheese.

The “musty potato” aroma first described in eggs and milk and other dairy products due to the growth of Pseudomonas graveolens (Pseudomonas taetrolens) continues to be reported as a defect in eggs and carcass meats. Pseudomonas perolens has been found to produce a similar aroma in spoiling fish. Vapors entrained from milk and fish tissue cultures of these organisms, collected on porous polymer traps and analyzed by GLC‐alkali flame and GLC‐MS systems, revealed both organisms produce 2‐methoxy‐3‐alkylpyrazines. 2‐Methyoxy‐3‐isopropylpyrazine was found to be responsible for the musty potato aroma. A possible mechanism for the formation of pyrazines is discussed.
Aerobic microbial growth in semisolid matrices: Heat and mass transfer limitation
Authors: Finger S. M. , Hatch R. T. , Regan T. M.
Published: December 2004

A conceptual model of aerobic microbial growth in semisolid matrices was developed as a first step in the prediction of the rate of breakdown of semisolid cellulosic material. The conceptual model was described by a series of equations simplified by the assumption of steady‐state microbial activity, and heat and mass transfer limitation. Temperature and oxygen distribution in compost piles were measured experimentally at the Butler County Mushroom Farm, Butler County, Pennsylvania, to test the validity of these assumptions. The compost piles consisted of ground corn husks, straw, and race horse manure. The data fit with the model was excellent with deviations between model predictions (as solved by an analog computer) and actual temperature measurements never exceeding 3°C. The effects of compost pile geometry, external temperature, compost density, external oxygen concentration, and insulation at the bottom of the pile were then predicted using a digital computer to solve the model. The predictions show that the maximum breakdown rate occurs for an optimum height (which depends upon the system), insulating the base increases the breakdown rate, increasing the external temperature increases the initial breakdown rate but decreases the pseudo‐steady‐state breakdown rate and the uniformity, and any increase in the external oxygen concentration increases the breakdown rate but decreases the uniformity.
Utilization of cellulosic materials through enzymatic hydrolysis. II. Preliminary assessment of an integrated processing scheme
Authors: Wilke Charles R. , Cysewski Gerald R. , Der Yang Ren , Von Stockar Urs
Published: December 2004

An integrated processing scheme is described for the conversion of a cellulosic waste (newsprint) to sugars by enzymatic hydrolysis and then to ethanol and yeast by fermentation. The unconverted solids are burned to produce process energy requirements and surplus electrical power. Preliminary designs and cost studies are developed to provide a rough perspective on the potential economic feasibility of this method of cellulose utilization.
Computer‐aided baker's yeast fermentations
Authors: Wang Henry Y. , Cooney Charles L. , Wang Daniel I. C.
Published: December 2004

The economics of yeast production depend heavily upon the cellular yield coefficient on the carbon source and the volumetric productivity of the process. The application of an on‐line computer to maximize these two terms during the fermentation requires a continuous method of measuring cell density and growth rate. U fortunately, a direct sensor for biomass concentration suitable for use in industrial fermentations is not available. Material balancing, with the aid of on‐line computer monitoring, offers an indirect method of measurement. Laboratory results from baker's yeast production in a 14‐liter fermentor (with a PDP‐11/10 computer for on‐line analyses) show this indirect measurement technique to be a viable alternative. From the oxygen uptake and carbon dioxide production data, gas flow rate, and ammonia addition rate, the cell density during the fermentation has been estimated and found to compare well with actual fermentation data.
Production of schardinger β‐dextrin by soluble and immobilized cyclodextrin glycosyltransferase of an alkalophilic Bacillus sp.
Authors: Nakamura N. , Horikoshi K.
Published: December 2004

Succiylated cyclodextrin glycosyltransferase (EC.3.2.1.19) of an alkalophilic Bacillus sp. was adsorbed on a vinylpyridine copolymer. The enzyme had about 25% of the activity of soluble enzyme added. No increase of pH or thermal stability of the enzyme was observed by the adsorption, whereas optimum temperature for the enzyme action was shifted from 50 to 55°C. The enzyme converted starch to cyclodextrins without significant loss of activity under the conditions of 4 times reusing of 6 hr conversion by the batch system or 2 weeks continuous reaction by the column system at 55°C and pH 8.0. About 46% of the potato starch solution [15% (w/v)] was converted to cyclodextrins by the enzyme, and 52% was converted by the simultaneous action of the enzyme and alkaline pullulanase of alkalophilic Bacullus sp.(No.202‐1). These values were almost the same as those obtained by the soluble enzyme or enzyme system.
A method using solubility to predict dry matter digestibility of cellulosic materials
Authors: Chiang Lin Chang , Dunlap Charles E.
Published: December 2004

A rapid chemical procedure based on the solubility of a holocellulose sample in a system of dimethyl sulfoxide with paraformaldehyde has been developed to provide a laboratory method for predicting dry matter digestibility of cellulose containing samples. The amount of dry matter solubilized by the chemical procedure was closely correlated with anaerobic, in vitro, rumen fluid digestion and with digestibility as measured by aerobic Cellulomonas, sp. bacteria. The quantity of solvent and dissolving time had little effect on solubility over a wide range. The method is rapid, well suited for various cellulosic materials, and may be carried out with simple equipment and facilities.
Performance of the continuous glucose isomerase reactor system for the production of fructose syrup
Authors: Ryu D. Y. , Chung S. H. , Katoh K.
Published: December 2004

Glucose isomerase in the form of heat‐treated whole‐cell enzyme prepared from Streptomyces phaeochromogenus follows the reversible single‐substrate reaction kinetics in isomerization of glucose to fructose. Based on the Kinetic constants determined and the mathematical model of the reactor system developed, the preformance of a plug‐flow‐type continuous‐enzyme reactor system was studied experimentally and also simulated with the aid of a computer for the ultimate objective of optimization of the glucose isomerase reactor system.

The enzyme decay function for both the enzyme storage and during the use in the continuous reactor, was found to follow the first‐order decay kinetics. When the enzyme decay function is taken into consideration, the ideal homogeneous enzyme reactor kinetics provided a satisfactory working model without further complicatin of the mathematical model, and the results of computer simulation were found to be in good agreement with the experimental results. Under a given set of constraints the performance of the continuous glucose isomerase reactor system can be predicted by using the computer simulation method described in this paper.

The important parameters studied for the optimization of reactor operation were enzyme loading, mean space time of the reactor, substrate feed concentration, enzyme decay constants, and the fractional conversion, in addition to the kinetic constants. All these parameters have significant effect on the productivity.

Some unique properties of the glucose isomerization reaction and its effects on the performance of the continuous glucose isomerase reactor system have been studied and discussed. The reaction kinetics of glucose isomerase and the effects of both the enzyme loading and the changes in reaction rate within a continuous reactor on the productivity are all found to be of particular importance to this enzyme reactor system.
Degradation of polysaccharides by endo‐ and exoenzymes: Dextran–dextranase model systems
Authors: Wheatley M. A. , Moo‐Young M.
Published: December 2004

Experiments were carried out on dextran–dextranase systems to test the prediction of a mechanistic model recently proposed by us, for the synergistic effect of combined exo/endo enzymic action in the degradation of polymeric substrate. Soluble forms of the substrate were used. Preliminary experiments with an insoluble form of the substrate were also carried out to demonstrate the applicability of the analytical techniques to these cases. Molecular weight distributions of the degradation products were determined (by gel‐permeation chromatography) and the rates of production of glucose and of other reducing sugars were also measured. It was found that the exodextranase alone had very little effect on the molecular weight distributions compared to a significant shift towards lower molecular weight obtained with the endodextranase which was synergistically enhanced by the action of the combined enzymes. Glucose was produced more rapidly by the exoenzyme compared to the endoenzyme, but combinations of the two enzymes gave a rate enhancement greater than the linear sum of the effects of the two individual enzymes. In comparing the degradation indices and polydispersities of the various degradation products, similar synergistic effects of the combined enzymes in accordance with the theoretical predictions, were observed. The practical implications of these findings to the design of fermentation processes which depend on the action of endo‐ and exoenzyme mixtures are noted.
Properties of enzymes immobilized by the diazotized m‐diaminobenzene method
Authors: Gray Charles J. , Livingstone Catherine M.
Published: December 2004

Some properties of a number of enzymes immobilized by the diazotized m‐diaminobenzene (dDAB) method are described. The pH‐activity profiles of β‐D‐glucosidase, glucoamylase, peroxidase, uricase, and D‐glucose oxidase were virtually unchanged on immobilization while those of catalase and dextranase were significantly altered. β‐D‐Glucosidase, glucoamylase, and glucose oxidase were found to be more susceptible to denaturation on lyophilization when immobilized than in the native state; however, sorbitol had a marked protective effect in every case examined. Sorbitol was also found to exert a stabilizing effect when lyophilized immobilized preparations were stored. Immobilization marginally improved the stabilities of a number of enzymes to heating at 60° at pH 8.0. The usefulness for continuous reaction of a column of glucoamylase attached to celite was established. The reuse of the solid supports was demonstrated.
An analysis of extended and exponentially‐fed‐batch cultures
Authors: Lim Henry C. , Chen Bill J. , Creagan Christopher C.
Published: December 2004

Under certain conditions it is shown that an extended culture is equivalent to an exponentially‐fed‐batch culture, that an exponentially‐fed‐batch culture (and an extended culture) can be maintained at a steady state and that an exponentially‐fed‐batch culture may be mimicked by a continuous‐flow culture with a constant dilution rate. Operational conditions required to maintain steady states are specified.
Computation of the fraction of induced cells in enzyme induction systems
Authors: Von Stockar Urs , Yang Ren Der , Wilke Charles R.
Published: December 2004

A theoretical model is developed for continuous multistage enzyme production systems, which consist of a growth fermentor used for growing microorganisms rapidly without enzyme production and a subsequent system of induction reactors in which enzymes induction and production occurs. The model allows the computation of the fraction of induced cells residing in the induction reactor for organisms exhibiting a lag phase in enzyme induction. For this model a general analytical solution was obtained for the cumulative internal residence time distribution of a series of n well‐stirred vessels with a recycle. The theoretical results are compared in a preliminary way with experimentally measured cellulase productivities of continuous multistage cellulose fermentations with Trichoderma viride QM 9414.
A reassessment of mixing cost in fermentation processes
Authors: Ryu Dewey Y. , Oldshue J. Y.
Published: December 2004

The gas–liquid oxygen transfer rate is a key step in the production of antibiotics in submerged fermentation. If the gas–liquid oxygen mass transfer rate is not equal to the required liquid–solid oxygen mass transfer rate at a particular cell concentration, then productivity of the particular fermentation operation will not be the maximum possible value.

One way to increase the productivity of a given fermentation tank installation is to increase the cell concentration and to increase the oxygen transfer by changing the mixer and air supply to match the new requirements. In order to evaluate the cost of making this change to the larger mixing equipment, a typical cost example is given which can easily be modified for other combinations of production cost and mixer cost. As an example, it is seen that a considerable savings can result from a given installation by primarily changing the oxygen transfer ability of the equipment to utilize a given fermentor more efficiently. Production cost savings of 8 to 25% are shown in the example cited.
The enzymatic conversion of L‐histidine to urocanic acid by whole cells of Micrococcus luteus immobilized on carbodiimide activated carboxymethylcellulose
Authors: Jack T. R. , Zajic J. E.
Published: December 2004

Whole cells of Micrococcus luteus (formerly Sarcina lutea ATCC 9341) have been covalently linked to a carboxymethylcellulose support system, with the retention of histidine ammonia–lyase activity. The dependence of the rate of urocanic acid formation on pH, temperature, and added surfactant concentration was similar for the free and the immobilized cells.

The immobilization procedure used is based on the carbodiimide activation of carboxymethylcellulose and has been optimized for the histidine ammonia–lyase activity of the immobilized cells on a given weight of cellulose.

In a column reactor at 23°C and superficial velocity of 0.044 cm/min, 5 g of cellulose with bound cells gave a 35% conversion of an L‐histidine solution (0.25M, pH 9.0) to urocanic acid for 16 days of continuous operation.

The scope of this carbodiimide assisted immobilization procedure has been investigated for a series of microorganisms and a variety of carboxylate functionalized supports.
Assimilation of liquid hydrocarbon by microorganisms. II. Growth kinetics
Authors: Miura Yoshiharu , Okazaki Mitsuo , Murakawa Shin‐Ichi , Hamada Shin‐Ichiro , Ohno Kyoko
Published: December 2004

The growth kinetics of a microorganism with high affinity for liquid hydrocarbon which has a low solubility in water was investigated for Candida intermedia IFO 0761 in our previous work.6 The microorganism contained a hydrocarbon pool in and/or on the cell. The transfer of water‐soluble substrates to the cell was not the rate‐limiting step in the growth of C. intermedia accompanied by clump formation with liquid hydrocarbon. The operating conditions necessary for the oxygen supply for the growth were adequate for the growth of C. intermedia on n‐tetradecane. The saturation kinetics was valid for the specific growth rate of C. intermedia and specific concentration of hydrocarbon per unit cell mass; the specific growth rate was expressed by the following equation:
Desorption of carbon dioxide from fermentation broth
Authors: Yagi Hideharu , Yoshida Fumitake
Published: December 2004

Rates of CO2 desorption from fermentation broths under actual operating conditions were determined by measuring the CO2 partial pressure in the exit gas. The concentrations of CO2 physically dissolved in the broths were measured by the so‐called tubing method. Values of kLa for CO2 desorption calculated from these values agreed well with the kLa values for oxygen absorption corrected for the difference in gas diffusivities. The dissolved CO2 concentration in the broth, which seems to bean important operating parameter, can easily be estimated from the CO2 partial pressure in the exit gas, a more easily measurable quantity, if the kLa value is known. For a given value of kLa, assumption of perfect mixing or plug flow in the gas phase made little difference in the calculated values of the dissolved CO2 concentration, indicating that the gas phase was probably in between perfect mixing and plug flow.

In industrial fermentors, the CO2 partial pressure in the exit gas can practically be assumed to be in equilibrium with the dissolved CO2 concentration.
Continuous manufacture of yogurt. I. Optimal conditions and kinetics of the prefermentation process
Authors: Driessen F. M. , Ubbels J. , Stadhouders J.
Published: December 2004

The principles of a method for the continuous manufacture of yogurt, based upon a two stage system, are given. The first stage, the prefermentation of milk at 45°C to a pH of 5.7, is described.

The limitations of this continuous prefermentation are experimentally determined. No change in the balance of the yogurt bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus, was observed. A mathematical approach is given for starting and stopping the process.
Methane fermentation of brewery by‐products
Authors: Keenan John D. , Kormi Iraj
Published: December 2004

A laboratory‐scale research program was undertaken to investigate the kinetics of the mesophilic (37°C) anaerobic digestion of brewery industry by‐product. The purpose was to develop data for the design and operation of full‐scale units which could be used to generate methane fuel gas from these materials. This is important because the brewery industry has been susceptible to shortages of natural gas in recent years. The minimum SRT is 2.3 days, although for design purposes as much as ten days is recommended. The biomass yield is 0.512 g volatile suspended solids (VSS)/g volatile solids (VS) or 0.421 g VSS/g chemical oxygen demand (COD). The maintenance requirement is 0.052 g VS/g VSS per day or 0.061 g COD/g VSS per day. The specific methane yield is 2.51 liter/g VSS, and the methane productivity is 0.32–0.41 liter/g dry substrate added or 0.69–0.91 liter/g destroyed. The maximum loading rate for which substrate inhibition is not observed is 6 g dry substrate added per liter per day. The results of the entire program indicate that processing brewery by‐product in this manner is both technically feasible and economically attractive.
Dynamic measurement of the volumetric mass transfer coefficient in agitated vessels: Effect of the start‐up period on the response of an oxygen electrode
Authors: Linek V. , Vacek V.
Published: December 2004

The response of a polarographic oxygen electrode to a step change and to an exponential change in bulk oxygen concentration was studied theoretically and experimentally for the case where there is a significant liquid film resistance at the outerside of the membrane‐covered electrode. The probe response has been described considering the start‐up period of the concentration changes (the period of time that will elapse before the new concentration level is established and/or before the volumetric mass transfer coefficient kLa regains its steady‐state value after the gas supply is opened to the fermentor). A linear change of the pertinent characteristics is assumed during this start‐up period. It is shown that a substantial error could be introduced by neglecting the start‐up period for cases frequently occurring in practice. In addition, the dependences of the probe response on the direct contact of bubbles with an electrode and on the fluid flow field around it were discussed.
Rapid ethanol fermentations using vacuum and cell recycle
Authors: Cysewski Gerald R. , Wilke Charles R.
Published: December 2004

Cell recycle and vacuum fermentation systems were developed for continuous ethanol production. Cell recycle was employed in both atmospheric pressure and vacuum fermentations to achieve high cell densities and rapid ethanol fermentation rates. Studies were conducted with Saccharomyces cerevisiae (ATCC No. 4126) at a fermentation temperature of 35°C. Employing a 10% glucose feed, a cell density of 50 g dry wt/liter was obtained in atmospheric‐cell recycle fermentations which produced a fermentor ethanol productivity of 29.0 g/liter‐hr. The vacuum fermentor eliminated ethanol inhibition by boiling away ethanol from the fermenting beer as it was formed. This permitted the rapid and complete fermentation of concentrated sugar solutions. At a total pressure of 50 mmHg and using a 33.4% glucose feed, ethanol productivities of 82 and 40 g/liter‐hr were achieved with the vacuum system with and without cell recycle, respectively. Fermentor ethanol productivities were thus increased as much as twelvefold over conventional continuous fermentations. In order to maintain a viable yeast culture in the vacuum fermentor, a bleed of fermented broth had to be continuously withdrawn to remove nonvolatile compounds. It was also necessary to sparge the vacuum fermentor with pure oxygen to satisfy the trace oxygen requirement of the fermenting yeast.
Considerations in predicting phenotypic modifications in amino acid profiles of total cell protein of microorganisms
Authors: Alroy Yair , Tannenbaum Steven R.
Published: December 2004

A mathematical model is presented that describes the concentration of an amino acid in total cell protein as a function of its concentration in individual cell proteins or in sets of cell proteins. The resulting equation makes it possible to calculate how the makeup of cell proteins must change to obtain a specified alteration in the content of an amino acid in the total cell protein. It is recognized that protein species or sets of proteins that are distinguished by being richer or poorer in a key amino acid than the overall protein must undergo considerable variations in content. The necessary extent of these shifts suggests that the amino acid composition of total cell protein is not likely to be affected significantly by variations in the cultivation conditions.
A new approach to preparative enzymatic synthesis
Authors: Klibanov Alexander M. , Samokhin Gennady P. , Martinek Karel , Berezin Ilya. V.
Published: December 2004

A new approach to preparative organic synthesis in aqueous–organic systems is suggested. It is based on the idea that the enzymatic process is carried out in a biphasic system “water–water‐immiscible organic solvent.” Thereby the enzyme is localized in the aqueous phase—this eliminates the traditional problem of stabilizing the enzyme against inactivation by a nonaqueous solvent. Hence, in contrast to the commonly used combinations “water–water‐miscible organic solvent,” in the suggested system the content of water may be infinitely low. This allows one to dramatically shift the equilibrium of the reactions forming water as a reaction product (synthesis of esters and amides, polymerization of amino acids, sugars and nucleotides, dehydration reactions, etc.) toward the products. The fact that the system consists of two phases provides another very important source for an equilibrium shift, i.e., free energies of the transfer of a reagent from one phase to the other. Equations are derived describing the dependence of the equilibrium constant in a biphasic system on the ratio of the volumes of the aqueous and nonaqueous phases and the partition coefficients of the reagents between the phases. The approach has been experimentally verified with the synthesis of N‐acetyl‐L‐tryptophan ethyl ester from the respective alcohol and acid. Porous glass was impregnated with aqueous buffer solution of chymotrypsin and suspended in chloroform containing N‐acetyl‐L‐tryptophan and ethanol. In water (no organic phase) the yield of the ester is about 0.01%, whereas in this biphasic system it is practically 100%. The idea is applicable to a great number of preparative enzymatic reactions.
Dynamics of a chemostat in which two organisms compete for a common substrate
Authors: Aris R. , Humphrey A. E.
Published: December 2004

When two organisms compete for a given substrate without preying on one another, the possible steady states depend on the relative disposition of the two growth curves and the position of the point (Z,θ), whose coordinates are the nutrient feed concentration and dilution rate. It is shown how the stability of each steady state can be understood and qualitative phase portraits can be drawn for each of the 31 distinct types of situations.
A dynamic kinetic model of the activated sludge process
Authors: Chase L. M.
Published: December 2004

A kinetic model has been developed which describes the dynamic response of activated sludge to changes in substrate concentration. The well known phenomenon of “growth‐rate hysteresis” can be explained by the simple yet biologically reasonable hypotheses of the model. Experimental results have verified the model quantitatively.
Theoretical conversion yields for penicillin synthesis
Authors: Cooney C. L. , Acevedo F.
Published: December 2004

The efficiency of conversion of the carbon‐energy source to product is of primary importance in many fermentation processes. In order to assess the efficiency of a process, one must know how close the actual conversion yield is to the theoretical maximum. Theoretical conversion yields are useful, therefore, as guides in improving a process. This knowledge is particularly important today because the cost of raw materials is rapidly rising. In this study, the biochemical pathway of penicillin synthesis was used to estimate the theoretical yield of penicillin from glucose, ammonia, and sulfate. These values are compared with experimental data from the literature. An analysis of the role of glucose in the synthesis of cell mass and penicillin and in the maintenance of cells makes it possible to assess the efficiency of carbon‐source utilization and to direct further advances in penicillin fermentations.
Modeling and simulation of oxygen transfer in airlift fermentors
Authors: Ho Chester S. , Erickson Larry E. , Fan L. T.
Published: December 2004

A mathematical model for simulation of oxygen transfer in airlift fermentors is presented. The airlift fermentor is represented by a number of interconnected compartments, each of which is assumed to be well mixed. In the annular region, the model includes both upflow and downflow for the gas phase. The model contains several adjustable parameters through which important hydrodynamic effects affecting oxygen transfer are incorporated. The effect of hydrostatic pressure is also included in the model. The model is simple enough to be used in design studies and it can be easily adapted to other airlift system configurations. The simulation results show good qualitative agreement with available experimental results.
Disintegration of microorganisms in an industrial horizontal mill of novel design
Authors: Rehacek J. , Schaefer J.
Published: December 2004

A continuous high‐speed horizontal colloid mill of novel design for use in the microbiological and food industries was tested for the disintegration of cells of Saccharomyces cerevisiae and Candida utilis. The mill consists of a horizontal vessel with round or oval cross sections fitted with a high‐speed longitudinal agitator shaft on which are mounted disk agitators, alternating radially and obliquely to the shaft. The mill is partly filled with freely moving grinding elements which, during a continuous operation, are maintained in the vessel by a vibrating annular slot separator. Highly efficient cooling is provided by circulation of cooling fluid through a jacket surrounding the vessel as well as through the agitator shaft and disks. The radial agitator disks impart a radial motion to the grinding elements, while the oblique disks give rise to the axial movement of a substantial part of the elements. The crossing of paths thus achieved gives the mill a very high efficiency. Using a mill of 20 liter nominal capacity, the effects of agitator design, agitator speed, flow rate, and concentration of the cell suspension on the disintegration efficiency and heat production were studied. Ninety per cent of S. cerevisiae cells in a 15% suspension could be broken at a residence time of 2.5 min. The temperature rise did not exceed 8° C. The corresponding figure for C. utilis was 84%. The maximal flow rate was 400 liter/hr. Extrapolation indicates that available industrial mills of 300 liter capacity based on the same design can handle flows of 2000 liter/hr.
Microbial electrode BOD sensors
Authors: Karube Isao , Matsunaga Tadashi , Mitsuda Satoshi , Suzuki Shuichi
Published: December 2004

Two different types of biochemical oxygen demand (BOD) sensors using microbial electrodes were prepared. First, a microbial electrode using the bacteria–collagen membrane and oxygen electrode was used for the determination of BOD. When the electrode was inserted in a sample solution containing glucose and glutamic acid (model waste water), the current of the electrode decreased markedly with time until a steady state was reached. A linear relationship was observed between the steady state current and the concentration of the standard solution containing glucose–glutamic acid or the BOD of the solution. The BOD of industrial waste waters can be estimated within 15 min by using the microbial electrode. No decrease in current output was observed over a ten day period. The reproducibility was determined using the same sample (10% of the standard solution) and was found to be 26.2 ± 2.0 μA (7.5% of the relative standard deviation). Next, a biofuel cell utilizing microbial electrode (immobilized Clostridium butyricum–platinum electrode) was applied to the estimation of the BOD of waste waters. The current of the biofuel cell was decreased markedly with time until a steady state was reached. The steady state current was in all cases attained within 30–40 min at 37°C. A linear relationship was obtained between the steady state current and BOD. The BOD of industrial waste waters can be estimated by using the biofuel cell. Relative error of the BOD estimation was within ±10%. The current output of the biofuel cell was almost constant for 30 days.
Toxic effects of fatty acids on yeast cells: Dependence of inhibitory effects on fatty acid concentration
Authors: Hundová Z. , Fencl Z.
Published: December 2004

The yeasts Saccharomyces cerevisiae, Candida utilis, and Candida lipolytica were used to investigate the action of different concentrations of fatty aeids (from acetic to myristic acid) on cell growth, division, uptake of inorganic phosphate, and substrate oxidation. The former two yeasts were found to undergo an inhibition of growth, cell division, and phosphate uptake at lower acid concentrations and to experience the inhibition of substrate oxidation at higher acid concentration. The concentration dependence of the action of fatty acids can be classified into four categories: (1) subthreshold concentrations which do not inhibit growth and have either no effect on, or stimulate, oxygen consumption; (2) threshold concentrations which lower the rate of growth, cell division, and phosphate uptake but do not inhibit the oxidation of carbon substrate; (3) above threshold concentrations which inhibit partially even substrate oxidation, and (4) microbicide concentrations. Candida lipolytica displays the Same sensitivity toward the action of fatty acids as the above yeast species; however, the threshold concentrations are higher and can be quickly lowered owing to oxidation by the yeast. The concentrations of fatty acids found in the medium after cultivations of yeast with n ‐alkanes are of the same order as limiting concentrations; the formation of acids with twelve and less carbons in the molecule can thus be assumed to be one of the basic reasons for the lowering of biomass yields during cultivations on these hydrocarbons.
Application of cyanide‐metabolizing enzymes to environmental control; enzyme thermistor assay of cyanide using immobilized rhodanese and injectase
Authors: Mattiasson Bo , Mosbach Klaus , Svenson Anders
Published: December 2004

The application of the enzyme thermistor in the analysis of cyanide in standard solutions as well as in blast furnace waste water is described. The heat signal is generated in the conversion of cyanide, catalyzed by the immobilized enzymes rhodanese (E.C. 2.8.1.1) and injectase (E.C. 4.4.19). Using the combination of cyanide‐metabolizing enzymes and the enzyme thermistor unit, assays down to 20μM cyanide can be carried out. Linear relationships were obtained at 20–600μM cyanide for injectase and 20–1000μM for rhodanese. The stability at 27°C of the heat response was initially decreased, but soon stabilized at about 80% of the initial value and remained so for at least 200 hr. The technique was easily adapted to continuous analysis, applicable to environmental control (e.g., a “cyanide guard”) with a response time at present within 2–3 min after a sudden change in cyanide concentration has appeared.
Transfer function matrix of the continuous cultivation system of Morchella crassipes in ammonia base waste sulfite liquor
Authors: Leduy A. , Kosaric N. , Zajic J. E.
Published: December 2004

A continuous stirred tank fermentor (CSTF) used for cultivation of the fungus Morchella crassipes in ammonia base waste sulfite liquor (NH3‐WSL) was considered as a multivariable linear system around its operating point. Pulse testing on the inputs (inlet jacket temperature, inlet pH, inlet substrate concentration) and their responses at the outputs (biomass, outlet temperature, outlet jacket temperature, outlet pH, outlet substrate concentration) were used for numerical determination of the transfer function matrix:
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Application of immobilized chymotrypsin in a multistage fluidized‐bed reactor
Authors: Halwachs W. , Wandrey C. , Schügerl K.
Published: December 2004

The stereospecific hydrolysis of D,L‐phenylalanine methylester with immobilized α‐chymotrypsin was carried out as a model reaction for the racemate resolution of aromatic amino acids in a five staged fluidized‐bed reactor (FBR). Owing to ester hydrolysis, a pH shift occurred along the reactor. Because of the pH‐dependent enzyme activity a particular longitudinal pH profile had to be enforced by a proper entrance pH in order to gain an optimum conversion. In the FBR with optimum pH profile, higher conversions were achieved than in a continuous stirred tank reactor (CSTR) at the pH optimum and at the same contact time. By the application of a proton balance and the results of kinetic measurements a model was developed for the prediction of the optimum longitudinal pH profile with regard to the maximum conversion.
Preparation and properties of immobilized papain and lipase
Authors: Kilara A. , Shahani K. M. , Wagner Fred W.
Published: December 2004

Papain and lipase were immobilized on derivatized Sepharose 4‐B. The activated agarose had a binding capacity of 1.2 μmol amino groups/ml packed agarose or 17 mg proteins/g dry agarose. The immobilized enzyme preparations were tested for the effects of pH of assay, temperature of assay, and substrate concentrations. The effect of 6M urea on the activity of papain was also determined. Soluble forms of the enzymes were used for comparison. Immobilization of the enzymes resulted in slightly different pH and temperature optima for activities. For immobilized papain Km (app) was similar to the one observed with soluble papain. Immobilization of lipase, however, caused a decrease in Km values. The immobilized enzyme preparations were stable when stored at 4°C and pH 7.5 for periods up to eight months. The soluble enzymes lost their activity within 96 hr under similar storage conditions. Immobilized papain did not lose any activity after treatment with 6M urea for 270 min, whereas soluble papain lost 81% of its activity after the urea treatment, indicating that the immobilization of papain imparted structural and conformational stability to this enzyme.
Effect of mass transfer resistance on the lineweaver–burk plots for flocculating microorganisms
Authors: Ngian K. F. , Lin S. H. , Martin W. R. B.
Published: December 2004

It is shown that the mass transfer resistance can significantly distort the linearity of the Lineweaver–Burk plot of the kinetic data for a microbial culture which forms aggregates. For small flocs, the linearity of the Lineweaver–Burk plot is largely retained, but a different slope and intercept will be obtained compared with flocs free from mass transfer resistance. For large flocs, the Lineweaver–Burk plot shows pronounced curvature at high limiting substrate concentrations. Hence, if the true intrinsic kinetic parameters are to be extracted from a highly flocculating microbial culture, sufficient agitation has to be provided to remove the effect of mass transfer resistance. If the behavior of the flocculating microbial culture is to be explored, additional values for some physical parameters, such as the effective diffusion coefficient of the substrate in floc, the floc density, and the mean floc radius, are needed.
Practical identifiability of growth and substrate consumption models
Authors: Nihtilä Markku , Virkkunen Jouko
Published: December 2004

The estimation of parameters in several dynamic models, which describe growth and substrate consumption, has been carried out using a modified Gauss–Newton‐type method. The four models considered are Monod, Contois, linear specific growth rate, and an enzyme kinetic model. The initial values of the differential equations are included in the parameter vector which will be estimated. The efficiency of the method and the confidence limits of the parameters were studied using simulated measurement noise. The experimental results describeTrichoderma viridegrowing on glucose as the main carbon source.
Selection of a chemically defined medium for submerged cultivation of Streptomyces aureofaciens with high extracellular caseinolytic activity
Authors: Laluce Cecilia , Molinari Rubens
Published: December 2004

A chemically defined medium was developed for the submerged cultivation of Streptomyces aureofaciens with a high secretion of caseinolytic activity. The medium composition is: 40 g/liter maltose; 1.640 g/liter L‐leucine (0.0125M); 1.765 g/liter L‐lysine (0.0125M); 6.976 g/liter K2HPO4(0.04M); 4 g/liter CaCO3; 0.2 g/liter MgSO4·7H2O; 0.01 g/liter ZnSO4·7H2O; 0.01 g/liter FeSO4·7H2O; 0.01 g/liter. MnSO4·H2O, and 0.005 g/liter CoSO4·7H2O. Quantitative correlations were established between the concentrations of nutrients in the medium and the secretion of proteolytic activity. In this medium the secretion of proteolytic activity parallels growth, reaching a maximum after 70 hr at 30°C in shaker cultures. The secretion appears to be an active process and to require aerobic conditions.