bluuebunny/crossref_metadata_2025 huggingface dataset:
A process for protein enrichment of cassava by solid substrate fermentation in rural conditions
Authors: Daubresse P. , Ntibashirwa S. , Gheysen A. , Meyer J. A.
Published: December 2004

An artisanal static process for protein enrichment of cassava by solid‐state fermentation, developed in laboratory and tested on pilot units in Burundi (Central Africa), provides enriched cassava containing 10.7% of dry matter protein versus 1% before fermentation. Cassava chips, processed into granules of 2–4‐mm diameter, are moistened (40% water content) and steamed. After cooling to 40°C, cassava is mixed with a nutritive solution containing the inoculum (Rhizopus oryzae, strain MUCL 28627) and providing the following per 100 g dry matter: 3.4 g urea, 1.5 g KH2PO4, 0.8 g MgSO4·7H2O, and 22.7 g citric acid. For the fermentation, cassava, with ca. 60% moisture content, is spread in a thin layer (2–3 cm thick) on perforated trays and slid into an aerated humidified enclosure. The incubation lasts ± 65 h. The production of protein enriched cassava is 3.26 kg dry matter/m2tray. The effects of the variation of the nutritive solution composition and the inoculum conservation period on the protein production are equally discussed.
Cadmium accumulation by a Citrobacter sp. immobilized on gel and solid supports: Applicability to the treatment of liquid wastes containing heavy metal cations
Authors: Macaskie L. E. , Wates J. M. , Dean A. C. R.
Published: December 2004

Polyacrylamide gel‐immobilized cells of a Citrobacter sp. removed cadmium from flows supplemented with glycerol 2‐phosphate, the metal uptake mechanism being mediated by the activity of a cell‐bound phosphatase that precipitates liberated inorganic phosphate with heavy metals at the cell surface. The constraints of elevated flow rate and temperature were investigated and the results discussed in terms of the kinetics of immobilized enzymes. Loss in activity with respect to cadmium accumulation but not inorganic phosphate liberation was observed at acid pH and was attributed to the pH‐dependent solubility of cadmium photsphate. Similarly high concentrations of chloride ions, and traces of cyanide inhibited cadmium uptake and this was attributed to the ability of these anions to complex heavy metals, especially the ability of CN− to form complex anions with Cd2+. The data are discussed in terms of the known chemistry of chloride and cyanide‐cadmium complexes and the relevance of these factors in the treatment of metal‐containing liquid wastes is discussed. The cells immobilized in polyacrylamide provided a convenient small‐scale laboratory model system. It was found that the Citrobacter sp. could be immobilized on glass supports with no chemical treatment or modification necessary. Such cells were also effective in metal accumulation and a prototype system more applicable to the treatment of metal‐containing streams on a larger scale is described.
Rules for optimization of biocatalysis in organic solvents
Authors: Laane Colja , Boeren Sjef , Vos Kees , Veeger Cees
Published: December 2004

General rules for the optimization of different biocatalytic systems in various types of media containing organic solvents are derived by combining data from the literature, and the logarithm of the partition coefficient, log P, as a quantitative measure of solvent polarity. (1) Biocatalysis in organic solvents is low in polar solvents having a log P < 2, is moderate in solvents having a log P between 2 and 4, and is high in a polar solvents having a log P > 4. It was found that this correlation between polarity and activity parallels the ability of organic solvents to distort the essential water layer that stabilizes the biocatalysts. (2) Further optimization of biocatalysis in organic solvents is achieved when the polarity of the microenvironment of the biocatalyst (log Pi) and the continuous organic phase (log Pcph) is tuned to the polarities of both the substrate (log Ps) and the product (log Pp) according to the following rules: |log Pi − log Ps| and |log Pcph − log Pp| should be minimal and |log Pcph − log Ps| and |log Pi − log Pp| should be maximal, with the exception that in the case of substrate inhibition log Pi, should be optimized with respect to log Ps In addition to these simple optimization rules, the future developments of biocatalysis in organic solvents are discussed.
Use of epifluorescence microscopy for characterizing the activity ofThiobacillus Ferrooxidanson iron pyrite
Authors: Yeh Timothy Y. , Godshalk John R. , Olson Gregory J. , Kelly Robert M.
Published: December 2004

The enumeration and characterization of microorganisms attached to solid surfaces have always presented significant difficulties. This is particularly true for micro organisms that are indigenous to coal mines and mineral deposits where metal sulfides are ubiquitous. The complications that arise are the result of the variety of inorganic compounds that are present in these environments, the harsh conditions under which the microorganisms proliferate, and the low cell densities to which they grow. The work presented here suggests that epifluorescence microscopy using acridine orange can be a useful probe to study acidophilic metal‐leaching bacteria. Experiments involving the growth ofThiobacillus ferrooxidanson iron pyrite are described which indicate a relationship between cell fluorescence color and bacterial activity. Both attached and free‐solution cell densities were determined throughout the course of the leaching process and considered along with changes in cell fluorescence color which might be associated with changes in intracellular pH. As such, epifluorescence microscopy, using acridine orange, can be used for assessing the activity ofT. ferrooxidanson iron pyrite as well as resolving the controversy concerning the significance of attachment during the leaching process.
Distribution of heparinase covalently immobilized to agarose: Experimental and theoretical studies
Authors: Bernstein Howard , Yang Victor C. , Langer Robert
Published: December 2004

An immobilized enzyme reactor has been developed to remove heparin, the anticoagulant that is required in all extracorporeal devices for patients undergoing open‐heart surgery or kidney dialysis. The device uses the enzyme heparinase (EC 4.2.2.7), which is covalently linked to agarose with cyanogen bromide. A critical parameter in the development of a model for the degradation of heparin catalyzed by immobilized heparinase is the radial concentration profile of the enzyme within the agarose matrix. Experimental determinations of bound enzyme con centrations have been conducted previously for several enzyme systems using radioactive or fluorescent labels. For the development of the heparinase reactor it is necessary to use catalytically but not electrophoretically pure enzyme, and thus it is not possible to use the labeling techniques. To obtain information about the bound enzyme distribution, an experimental study of the intrinsic binding kinetics of heparinase to cyanogen bromide‐activated agarose was conducted. The binding reaction was studied as a function of both the concentration of heparinase and the gel‐reactive group. At conditions of functional group excess, the binding kinetics were pseudo first order in heparinase concentration with a rate constant equal to 0.12 Ccn (h−1), where Ccn is the gel‐reactive group concentration. The reactive group concentration remained constant within the 2–4‐h experiments. Competitive binding between heparinase and the protein contaminants was unimportant. A model was formulated for the immobilization procedure based on the diffusion of heparinase within the porous network and the binding kinetics as determined above. The model predicted the immobilization of heparinase to be kinetically controlled and the enzyme to distribute uniformly within the agarose matrix. These experimental techniques could be applied to predict the immobilized enzyme distribution for different enzyme systems that are not electrophoretically pure.
Combined submerged and solid substrate fermentation for the bioconversion of lignocellulose
Authors: Viesturs U. E. , Strikauska S. V. , Leite M. P. , Berzins A. J. , Tengerdy Robert P.
Published: December 2004

A novel two‐stage bioreactor has been designed for a combined submerged (SF) and solid substrate fermentation (SSF) of wheat straw. The straw was pretreated with steam, and cellulases from the culture fluid of Trichoderma reesei were adsorbed on it for increased bioconvertibility. SSF was conducted in the top part of the bioreactor by inoculating the straw with a 36‐h mycelial culture of T. reesei, or Coriolus versicolor. In the bottom part of the fermenter, Endomycopsis fibuliger was grown in SF. The SF liquor was recirculated through the SSF stage at 24 h intervals to remove glucose and other metabolites that may inhibit growth, and to maintain optimum moisture level and temperature. The removed glucose and other metabolites provided nutrients for the yeast in the SF stage. The combined fermentation resulted in overall higher biomass yield, increased bioconversion, increased cellulase production, and increased digestibility compared with single SSF or SF.
Methanogenesis from volatile fatty acids in downflow stationary fixed‐film reactor
Authors: Bhadra Amit , Scharer Jeno M. , Moo‐Young Murray
Published: December 2004

Methanogenesis was studied in downflow stationary fixed‐film bioreactors. The support materials in this study included ceramic Raschig rings, hardwood chips, and sized charcoal. The performances of these support materials have been compared using both synthetic acid mixture and acid products obtained from paper mill sludge. Woodchips appeared to be the most promising support material: The maximum methane productivity of 3.56 L/L day at a nominal retention time of 0.78 day was obtained using initial total acid concentrations of 9.125 g/L. Higher productivity was achieved at the cost of efficiency of the process in terms of conversion of acids. From nitrogen balances, it was deduced that ammonia supplemented methane generation by supplying hydrogen for there duction of carbon dioxide.

An ionic balance was developed to ascertain the relationship between the composition and the pH of the liquid and the mole fraction of carbon dioxide in the gas phase. From these ionic balance equations, it was possible to predict the gas phase composition at various retention times. The maximum error between the computed and the experimental values was less than 13%.
Kinetic expression for maltose production from soluble starch by simultaneous use of β‐amylase and debranching enzymes
Authors: Shiraishi Fumihide , Kawakami Koei , Yuasa Akio , Kojima Tsuyoshi , Kusunoki Koichiro
Published: December 2004

The kinetics of the hydrolysis of soluble starch by simultaneous use of β‐amylase and either isoamylase or pullulanse was studied experimentally for a wide range of subtrate and enzyme concentrations. A kinetic expression was constituted for maltose production by β‐armylase, which was stimulated by an increase in linear linkage portions due to the debranching enzyme on amylopectin molecules. As a result, calculations by the kinetic expression agreed with time course data under various conditions.
Continuous cellulase production by immobilized Sporotrichum cellulophilum and continuous saccharification of bagasse
Authors: Tamada Masao , Kasai Noboru , Kaetsu Isao
Published: December 2004

Immobilized Sporotrichum cellulophilum with nonwoven materials was cultured continuously by a rotating‐disk fermentor to supply cellulase into the saccharification system. The filter paper activity (5.0) was retained after 696 h under conditions of 250 rpm stirring and 0.014 h−1 dilution rate. The product of the culture was supplied continuously to the saccharification reactor and used for the saccharification of bagasse. A glucose solution of ca. 0.9% was obtained continuously from 5% bagasse slurry during 610 h saccharification by this method.
Mathematical modelization of a packed‐bed reactor performance with immobilized yeast for ethanol fermentation
Authors: Gòdia F. , Casas C. , Solà Ç.
Published: December 2004

The performance of a continuous vertical packed‐bed reactor with yeast immobilized in carrageenan gel beads is reported. The study focuses on the mathematical modelling of the steady‐state fermentor behavior by means of a tanks‐in‐series model which includes the intrinsic kinetic model and the external mass transfer and internal diffusion‐reaction conditions in the beads.
A novel technique for measuring solute diffusivities in entrapment matrices used in immobilization
Authors: Merchant F. J. A. , Margaritis A. , Wallace J. B. , Vardanis A.
Published: December 2004

A novel technique has been developed for measuring effective solute diffusivities in entrapment matrices used for cell immobilization. In this technique radiotracers were used to measure effective diffusivities and equilibrium partition coefficients of the solute between the liquid and solid matrix. Ca‐alginate was used in this study, because it is one of the most commonly employed matrices for the immobilization of microbial, plant and mammalian cells. The experimental apparatus consisted of a single spherical Ca‐alginate bead which was attached to a rotating rod and immersed in water containing C14‐glucose. The rotational speed of the spherical bead was controlled and resulted in excellent mixing, and negligible external film mass transfer resistance, which allowed the measurement of true effective solute diffusivity within the solid matrix. The rates of C14‐glucose diffusion within the Ca‐alginate sphere were measured using a scintillation spectrometer. A mathematical model of unsteady‐state diffusion in a sphere was used with appropriate boundary conditions, and the effective diffusivity of glucose was found from the best fit of the experimental data using a computer regression analysis method. Using 2% (w/v) Ca‐alginate beads in this new radiotracer technique the effective diffusivity and partition coefficient of glucose were found to be 6.62 × 10−10 m2/s and 0.98, respectively. The accuracy, advantages, and simplicity of this new method for diffusivity measurements are also compared to other existing methods.
Microheterogeneity of enzymes and deactivation
Authors: Sadana Ajit , Malhotra Arun
Published: December 2004

The influence of microheterogeneity on enzyme inactivation kinetics is presented. Examples of different enzymes are given where microheterogeneity has been detected by different techniques. The different statistical models are presented which include the influence of microheterogeneity on enzyme inactivation kinetics and stability. As the microheterogeneity of the enzyme increases, there is a sharper decline in the normalized activity during the initial stages of the deactivation but a greater stability and activity, compared to similar homogeneous enzyme, as the deactivation proceeds. Microheterogeneity makes the deactivation reaction have a higher apparent order of reaction. The implications of microheterogeneity on enzyme inactivations are high lighted by different examples. The analysis provides fresh physical insights into the chemistry, subpopulations, structure, and function of enzymes.
Thermochemical pretreatment of lignocellulose to enhance methane fermentation: I. Monosaccharide and furfurals hydrothermal decomposition and product formation rates
Authors: Baugh Kent D. , McCarty Perry L.
Published: December 2004

Over a pH range 1–4 and temperatures from 170 to 230°C, the decomposition rates of xylose, gaiactose, mannose, glucose, 2‐furfural, and 5‐hydroxymethyl‐2‐furfural (5‐HMF) were pseudo first order. The effect of temperature and pH on the pseudo first‐order decomposition rate constants was modeled using the Arrhenius equation and acid‐base catalysis, respectively. Decomposition rates of the monosaccharides were minimum at a pH 2–2.5. Above pH 2.5, the monosaccharide decomposition was base catalyzed, with acid catalysis occurring at a pH of less than 2 for glucose. The furfurals were subject to acid catalysis at below ca. pH 3.5. The hydrothermal conversion of glucose to its decomposition products during thermochemical Pretreatment can be modeled as a combination of series and parallel reactions. The formation rates of identified soluble products from glucose decomposition, 5‐HMF and levulinic acid, were also functions of temperature and pH. The rate of 5‐HMF formation relative to glucose decomposition decreased as the pH increased from 2.0 to 4.0, with levulinic acid formation only detected when the pH was 2.5 or less. For glucose decomposition, humic solids accounted for ca. 20% of the decomposition products.
Selection of thermotolerant yeast strains for simultaneous saccharification and fermentation of cellulose
Authors: Szczodrak J. , Targoński Z.
Published: December 2004

A total of 58 yeast strains from 12 genera were assayed for their ability to grow and ferment carbohydrates in standard Durham tube test at 40, 43, and 46°C. Based on the kinetic parameters for glucose fermentation in shaken flask cultures, the strain Fabospora fragilis CCY51‐1‐1 was chosen for further studies. It reached about 56.0 and 35.0 g ethanol/L from ∼140 g glucose/L at 43 and 46°C in less than 48 h, respectively. Trichoderma reesei cellulase preparation (400 FPU/L) had not distinct effect on the ethanol yield and biomass production by the selected strain in the first 12 h fermentation at 46°C. Later a negligible decrease in both yields was observed. It was found that Fabospora fragilis did not grow or produce ethanol at 46°C as tho initial ethanol concentration overcame 40 g/L.
Hydrolysis of beef tallow by lipase from Pseudomonas sp.
Authors: Kosugi Yoshitsugu , Suzuki Hideo , Funada Tadashi
Published: December 2004

The lipase produced by Pseudomonas fluorescens biotype I was selected for hydrolyzing beef tallow at 50–70°C to more than 90% of reaction ratio. Using an amount of lipase sufficient to reach equilibrium, the final reaction ratio was decreased with increasing temperature and the apparent enthalpy of beef tallow hydrolysis obtained by the final reaction ratio was −1.93 × 104cal/mol, and the final reaction ratio also decreased with increasing substrate concentration. The rising time, which is the reaction time up to one‐half of the final reaction ratio, decreased remarkably with increasing temperature, and was closely related to the value of the maximum velocity by the Michaelis constant of this lipase. The final reaction ratio increased with increasing lipase amount up to equilibrium. Increasing the lipase above the amount required to reach equilibrium caused a decrease in the rising time. The feasibility of using parameters obtained by a hyperbolic simulation of the progress curve is discussed.
High‐pressure—temperature bioreactor for studying pressure—temperature relationships in bacterial growth and productivity
Authors: Miller Jay F. , Almond Edward L. , Shah Nilesh N. , Ludlow Jan M. , Zollweg John A. , Streett William B. , Zinder Stephen H. , Clark Douglas S.
Published: December 2004

Thermophilic organisms offer many potential advantages for biotechnological processes; however, realization of the promise of thermophiles will require extensive research on bacterial thermophily and high‐temperature cultivation systems. This article describes a novel bioreactor suitable for precise studies of microbial growth and productivity at temperatures up to 260°C and pressures up to 350 bar. The apparatus is versatile and corrosion resistant, and enables direct sampling of both liquids and gases from a transparent culture vessel without altering the reaction conditions. Gas recirculation through the culture can be controlled through the action of a magnetically driven pump. Initial studies in this bioreactor of Methanococcus jannaschii, an extremely thermophilic methanogen isolated from a deep‐sea hydrothermal vent, revealed that increasing the pressure from 7.8 to 100 bar accelerated the production of methane and cellular protein by this archaebacterium at 90°C, and raised the maximum temperature allowing growth from 90 to 92°C. Further increases in pressure had little effect on the growth rate at 90°C.
A continuous affinity ultrafiltration process for trypsin purification
Authors: Luong J. H. T. , Male K. B. , Nguyen A. L.
Published: December 2004

A continuous process has been devised and tested for purification of a crude trypsin preparation from pig pancreas. The development was based on the principles of affinity chromatography and Ultrafiltration. Trypsin was selectively attracted by a water‐soluble high molecular weight (>100,000) polymer, bearing a potent and specific trypsin inhibitor, m‐aminobenzamidine. The trypsin‐macroligand complex was then retained by using an appropriate Ultrafiltration membrane, while impurities could pass through. The bound trypsin was eluted by either arginine or benzamidine. The process also featured provision for recirculation of the eluant as well as the macroligand. It was demonstrated that this purification process could purify trypsin from the crude preparation with a yield of 77%, contaminated with only 3% of impurities. For the first time, a serious attempt has been made toward continuous purification of enzymes by the affinity Ultrafiltration technique. Besides a substantial increase in productivity, the affinity polymer could be easily reconditioned and expected to possess a long operative life. Such characteristics undoubtedly will play an important role in reducing the cost of trypsin purification.
Enzyme hydrolysis of plasma proteins in a CSTR ultrafiltration reactor: Performances and modeling
Authors: Bressollier Ph. , Petit J. M. , Julien R.
Published: December 2004

By investigating the effects of four operating variables—volume (V), Ultrafiltration flux (J), enzyme concentration (E), and substrate concentration (S)—on capacity (K) and conversion rate (ε) of a hollow fiber CSTR, the performances of the CSTR and the kinetic constants of the reaction were determined. A model which takes into account the course of fractional conversion (X) according to the modified space–time parameter, τ (integrated form of V, J, S, and E), was devised by employing the relationship to integrate the equation for the reaction rate of the CSTR and the expression of the modified space time. Correlation of this model and the experimentally obtained results demonstrates that the characteristics for an ultrafiltration membrane reactor for enzymatic hydrolysis by alcalase of plasma proteins are close to those of an ideal CSTR. Optimal scaling up, however, remains dependent on the compromise which may be obtained between capacity and the conversion rate.
On the optimal control of fed‐batch reactors with substrate‐inhibited kinetics
Authors: Cazzador Lorenzo
Published: December 2004

The optimal feed rate profiles, for fed‐batch fermentation that maximizes the biomass production and accounts for time, are analyzed. The solution can be found only if the final arc of the optimal control is a batch arc, since in this case the final concentrations of substrate and biomass can be determined by ulterior conditions on the mass balance and on the final growth rate of biomass and thus it is possible to solve the resulting time optimal problem by using Green's theorem. This evidences the “turnpike property” of the solution, which tries to spend the maximum time on or at least near the singular arc along which the substrate concentration is maintained constant. The optimality of the final batch arc is related to the time operational cost in the performance index. The sequence of the control depends on the initial conditions for which six different regions, with the respective patterns, have been identified, in case the performance index allows the control sequence to have a final batch.
Improved performance in viscous mycelial fermentations by agitator retrofitting
Authors: Buckland B. C. , Gbewonyo K. , Dimasi D. , Hunt G. , Westerfield G. , Nienow A. W.
Published: December 2004

For viscous mycelial fermentations it was demonstrated at the pilot‐plant scale that the replacement of standard radial flow Rushton turbines with larger diameter axial‐flow Prochem hydrofoil impellers significantly improved oxygen transfer efficiency. It was also determined that the Streptomyces broth under evaluation is highly shear thinning. Separate experiments using a Norcardia broth with similar Theological properties demonstrated that the oxygen transfer coefficient, KLa, can be greatly increased by use of water additions to reduce broth viscosity. These observations are consistent with the hypothesis that the improvement in oxygen transfer by changing agitator types is primarily due to an improvement in bulk mixing. A model is presented, based on the concepts of Bajpai and Reuss, which explains this improvement in performance in terms of enlargement of the well mixed micromixer region for viscous mycelial broths.
Stability and expression of a plasmid‐containing killer toxin cDNA in batch and chemostat cultures of saccharomyces cerevisiae
Authors: Lee Fang‐Jen S. , Hassan H. M.
Published: December 2004

A chimeric plasmid (pYT760‐ADH1) containing the yeast killer toxin–immunity cDNA was transformed into a leucine–histidine mutant (AH22) and into four industrial toxin‐sensitive yeasts. The chimeric plasmid was very stable and expressed toxin production (89.5 ± 4.8% killer cells) in two of the transformed yeasts that contained the 2μ plasmid, but was lost within 10 generations from two other transformed pickle yeasts that did not contain the 2μ plasmid. It suggested that plasmid stability was dependent on the presence of the 2μ plasmid which is naturally present in some yeasts. The plasmid was extremely stable (100% killer cells) and expressed more toxin in the mutant strain AH22. The effects of dilution rate, D(h−1) on plasmid stability and toxin expression were studied in transformed AH22 (AH22/T3) and Montrachet 522 (522/T1) wine yeast grown in glucose‐limited chemostat cultures. The results show that killer toxin production by AH22/T3 cells increased as a function of D(h−1) and that plasmid stability reached 100% at D ≥ 0.09 ± 0.01 h−1. However, with Montrachet 522/T1 transformed cells, 100% plasmid stability was seen at D ≥ 0.18 ± 0.02. h−1. We also challenged the AH22/T3 in chemostat culture (D = 0.25 h−1) with an equal number of untransformed cells (AH22). Transformed cells dominated the population (100%) within 8–10 h of growth, a time equivalent to two mean residence time.
Bioreactor considerations for secondary metabolite production from plant cell tissue culture: Indole alkaloids from Catharanthus roseus
Authors: Payne Gregory F. , Payne Nadine N. , Shuler Michael L.
Published: December 2004

Batch shake flask studies with Catharanthus roseus demonstrated that alkaloid production commenced only after growth had slowed or ceased. To obtain high alkaloid productivities for extended periods, a hormone‐free production medium was used. To develop a readily scalable process, both immobilized and suspended cell systems were studied. In the immobilized cell systems, growth, glucose utilization, and alkaloid production were suppressed; for the case of membrane entrapped cells this suppression was observed to be reversible. Based on the oxygen requirements of the cells, and the oxygen transfer capabilities of a pneumatically agitated bubble column, conditions were established that allowed the growth and production dynamics observed in shake flasks to be reproduced in the air sparged column reactor. The requirement for the aseptic exchange of growth for production medium was satisfied by using a coarse cotton filter and coupling filtration to aeration. With this filtration system, media can be rapidly and completely exchanged and the filter can be quickly and effectively backwashed. By coupling filtration to aeration, a two‐stage batch operation can be employed while requiring only a single bioreactor. Studies with this system demonstrated its capabilities for alkaloid production.
Performance of membrane fixed biocatalyst reactors. I: Membrane reactor systems and modelling
Authors: Prenosil J. E. , Hediger T.
Published: December 2004

Enzymatic membrane reactors are discussed according to the state of biocatalyst and driving force of reaction. Particular attention is given to the Capillary Membrane Fixed Enzyme Reactor (CAMFER) for its favorable characteristics. It is shown that, for a practical range of operation conditions, both kinetic and mass transfer effects must be considered simultaneously. Three modes of operation were investigated in detail using enzymatic lactose hydrolysis as a model reaction: Diffusional reactor, Recycle reactor, and Backflush reactor. In the comparison, superior performance of the CAMFER in diffusional mode was clearly demonstrated.
Selective adsorption of plant products
Authors: Payne G. F. , Shuler M. L.
Published: December 2004

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

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

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

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

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

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

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

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

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

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

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

A mathematical model that describes the adsorption and wash stages of biospecific adsorption (affinity chromatography) in a packed column is presented. The model expressions account for film and pre diffusion mass transfer as well as for different mechanisms of interaction between the adsorbate(s) and the ligand. The model equations may be applicable to single and multi‐component biospecific adsorption systems involving both monovalent and multivalent adsorbates.

The results obtained from model simulations show that the breakthrough time of the adsorbate is significantly influenced by the rate of the interaction step between the adsorbate and the ligand. The results indicate that when short beds are employed, then the choice of ligand with respect to its rate of interaction with the adsorbate may be of paramount importance. In certain systems involving bivalent adsorbates, the adsorbate may be displaced from the one‐site complex, reenter the flowing fluid stream, and increase the effluent adsorbate concentration above its inlet value. It is also shown that when a single column is divided into two beds operating in a periodic counter current mode, the ligand utilization can be almost four times higher than that obtained in a column of the same length operating in the fixed bed mode.

The studies on the wash stage indicate that the reduction of the concentration of the contaminant to a specified low level may be accomplished for certain systems in a shorter time, if the direction of flow in the wash stage is opposite to that used in the adsorption stage. However, a larger amount of product will be lost, in general, when the direction of flow of the washing medium is opposite to that employed during the adsorption stage.
Effect of pore size in substrate and diffusion of enzyme on hydrolysis of cellulosic materials with cellulases
Authors: Tanaka Mitsuo , Ikesaka Makoto , Matsuno Ryuichi , Converse Alvin O.
Published: December 2004

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

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