bluuebunny/crossref_metadata_2025 huggingface dataset:
Fuel ethanol and high protein feed from corn and corn–whey mixtures in a farm‐scale plant
Authors: Gibbons William R. , Westby Carl A.
Published: December 2004

Distiller's wet grain (DWG) and 95% ethanol were produced from corn in a farm‐scale process involving batch cooking–fermentation and continuous distillation–centrifugation. The energy balance was 2.26 and the cost was $1.86/gal (1981 cost). To improve the energy balance and reduce costs, various modifications were made in the plant. The first change, back‐end (after liquefaction) serial recycling of stillage supernatant at 20 and 40% strengths, produced beers with 0.2 and 0.4% (v/v) more ethanol, respectively, than without recycling. This increased the energy balance by 0.22–0.43 units and reduced costs by $0.07–$0.10/gal. The DWGs from back‐end recycling had increased fat. The second change, increasing the starch content from 17–19% to 27.5%, increased the ethanol in the beer from 10.5–14.9% at a cost saving of $0.41/gal. The energy balance increased by 1.08 units. No significant change was seen in DWG composition. The third change, using continuous cascade rather than batch fermentation, permitted batch‐levels of ethanol (10%) in the beer but only at low dilution rates. Both the cost and energy balance were decreased slightly. The DWG composition remained constant. The last change, replacing part of the corn and all of the tap water in the mash with whole whey and using Kluyveromyces fragilis instead of Saccharomyces cerevisiae during fermentation, resulted in an energy balance increase of 0.16 units and a $0.27/gal cost reduction. Here, 10% ethanolic beers were produced and the DWGs showed increased protein and fat. Recommendations for farm‐scale plants are provided.
Alkaline peroxide delignification of agricultural residues to enhance enzymatic saccharification
Authors: Gould J. Michael
Published: December 2004

Approximately one‐half of the lignin and most of the hemicellulose present in agricultural residues such as wheat straw and corn stover are solubilized when the residue is treated at 25°C in an alkaline solution of hydrogen peroxide. The delignification reaction is most efficient when the ratio of hydrogen peroxide to substrate is at least 0.25 (w/w) and the pH is 11.5. The supernatant fraction from a given pretreatment, after addition of makeup peroxide and readjustment of the pH, can be recycled to treat at least six additional batches of substrate, resulting in a substantial concentration of hemicellulose and soluble lignin degradation products. Hydrolysis of the insoluble fraction with Trichoderma reesei cellulase after alkaline peroxide treatment yields glucose with almost 100% efficiency, based upon the cellulose content of the residue before treatment. These data indicate that alkaline peroxide pretreatment is a simple and efficient method for enhancing the enzymatic digestibility of lignocellulosic crop residues to levels approaching the theoretical maximum.
Mathematical modeling of diffusion and reaction in the hydrolysis of vegetable protein in an immobilized enzyme recycle reactor
Authors: Adu‐Amankwa B. , Constantinides A.
Published: December 2004

Experimental investigation is by far the most effective approach for studying the behavior of physical systems. However, an enzymatic solubilization of vegetable protein is a complex combination of intrinsic problems, of which many are not easily adaptable to experimental investigation. Experimental designs to study enzyme vegetable protein reactions yield data which describe the extramembraneous activity of the immobilized enzyme. In a continuous recycle immobilized enzyme reactor, the microenvironment concentration of the substrate or product in the membrane phase, or the concentrations along the reactor axial length in the bulk phase are not discernible to the experimenter. However, the knowledge of such concentration profiles is important in weighing the significance of such factors as intermembrane diffusion, enzyme loading, wet membrane size, and the mode of operation of the reactor. The simulation of mathematical models, which describe the physical system within the constraints imposed, yields information which is vital to the understanding of the process occurring in the reactor. The kinetics and diffusion of an immobilized thermophilic Penicillium duponti enzyme at pH 3.4–3.7 and 50°C was modeled mathematically. The kinetic parameters were evaluated by fitting a model to experimental data using nonlinear regression analysis. Simulation profiles of the effects of reactor geometry, substrate concentration, membrane thickness, and enzyme leading on the hydrolysis rate are presented. From the profiles generated by the mathematical model, the best operational reactor strategy is recommended.
Kinetic studies of corn stover saccharification using sulphuric acid
Authors: Bhandari Nandan , Macdonald Douglas G. , Bakhshi Narendra N.
Published: December 2004

The kinetics of crystalline cellulose and hemicellulose hydrolysis in corn stover were studied with a nonisothermal technique. Reactions were arrested at temperatures between 160 and 240°C and product sugars were analyzed using a Bio‐Rad HPX‐85 liquid chromatographic column. A simple first‐order series reaction model was used for both cellulose and hemicellulose hydrolysis reactions. Kinetic parameters were obtained for three different sulphuric acid concentrations (0.49, 0.92, and 1.47 wt %). Activation energies remained constant over this acid concentration range but the preexponential factors showed an increase with acid concentration. Relationships were obtained between the preexponential factors and acid concentrations. Cellulose hydrolysis and glucose degradation reactions were observed to be of higher order with respect to acid concentration in comparison with the previous studies with other raw materials.
Cellobiose hydrolysis using Pichia etchellsii cells immobilized in calcium alginate
Authors: Jain D. , Ghose T. K.
Published: December 2004

The rate of celluose degradation, limited due to the inhibition by cellobiose, can be increased by the hydrolysis of cellobiose to glucose using immobilized β‐glucosidase. Production of β‐glucosidase in four yeasts was studied and a maximum activity of 1.22 IU/mg cells was obtained in cells of Pichia etchellsii when grown on 3% cellobiose as the sole carbon source. A study of the immobilization of β‐glucosidase containing cells of Pichia etchellsii on various solid supports was conducted and immobilization by entrapment in calcium alginate gel beads was found to be the most simple and efficient method. A retention of 96.5% of initial activity after ten sequential batch uses of the immobilized preparation was observed. The pH and temperature optima for free and immobilized cells were the same, i.e., 6.5 (0.05M Maleate buffer) and 50°C, respectively. Even though the temperature optimum was found to be 50°C, the enzyme exhibits a better thermal stability at 45°C. Beads stored at 4°C for six months retain 80% of their activity. Kinetic studies performed on free and immobilized cells shown that glucose is a noncompetitive product inhibitor.

The immobilized preparation was found to be limited by pore diffusion but exhibited no film‐diffusion resistance during packed bed column indicated by a low dispersion number of 0.1348. A model for reaction with pore diffusion for a noncompetitive type of inhibited system was developed and applied to the cellobiose hydrolysis system. The rate of reaction with diffusional limitations was determined by using the model and effectiveness factors were calculated for different particle sizes. An effectiveness factor of 0.49 was obtained for a particle diameter of 2.5 mm. The modified rate expression using the effectiveness factor represented batch and packed bed reactor operation satisfactorily. The productivity in the packed bed column was found to fall rapidly with increase in conversion rate indicating that the operating conditions of the column would have to be a compromise between high conversion rates and reasonable productivity. A half‐life of over seven days was obtained at the operating temperature of 45°C in continuous operation of the packed bed reactor. However, the half‐life in the column was found to be greatly affected by temperature, increasing to over seventeen days at a temperature of 40°C and decreasing to less than two days at 50°C.
Production of 2,3‐butanediol from D‐xylose by Klebsiella oxytoca ATCC 8724
Authors: Jansen Norman B. , Flickinger Michael C. , Tsao George T.
Published: December 2004

It is known that 2,3‐butanediol is a potentially valuable chemical feedstock that can be produced from the sugars present in hemicellulose and celluose hydrolysates. Klebsiella oxytoca is able to ferment most pentoses, hexoses, and disaccharides. Butanediol appears to be a primary metabolite, excreted as a product of energy methabolism. The theoretical maximum yield of butanediol from monosaccharides is 0.50 g/g. This article describes the effects of pH, xylose concentration, and the oxygen transfer rate on the bioconversion of D‐xylose to 2,3‐butanediol. Product inhibition by butanediol is also examined. The most important variable affecting the kinetics of this system appears to be the oxygen transfer rate. A higher oxygen supply favors the formation of cell mass at the expense of butanediol. Decreasing the oxygen supply rate increases the butanediol yield, but decreases the overall conversion rate due to a lower cell concentration.
Immobilization of yeast pyridoxaminephosphate oxidase to halogenoacetyl polysaccharides
Authors: Tsuge H. , Okada T.
Published: December 2004

Pyridoxaminephosphate oxidase (EC 1.4.3.5, deaminating) that was partially purified about 40‐fold from dry baker's yeast was immobilized to iodo‐ and bromoacetyl polysaccharides. The most effective carrier was an iodoacetyl cellulose, to which almost complete activity of pyridoxine 5′‐phosphate oxidase was immobilized in 0.02M potassium phosphate buffer (pH 8.5) containing 2M ammonium sulfate at 4°C. The immobilized enzyme was more stable than the purified, soluble enzyme against heat and pH change. It was confirmed that N‐(5′‐phosphopyridoxyl)‐L‐serine was degradedly oxidized to pyridoxal 5′‐phosphate and L‐serine by the immobilized enzyme as comparable rate as pyridoxine 5′‐phosphate, whereas N‐(5′‐phosphopyridoxyl)‐D‐serine did not serve as substrate, as in the purified, soluble enzyme.
Estimation and control techniques for continuous culture fermentation processes
Authors: Gallegos Jaime Alvarez , Gallegos Joaquin Alvarez
Published: December 2004

This article presents results obtained when some modern estimation and control techniques are applied to a simulated fermentation process. The control structure uses a particular observer of the substrate concentration and assumes the biomass concentration is measurable. The overall structure has been tested for both external and parametric disturbances, with very good results.
Peroxidase‐catalyzed color removal from bleach plant effluent
Authors: Paice M. G. , Jurasek L.
Published: December 2004

Effluent from the caustic extraction stage of a bleach plant is highly colored due to the presence of dissolved products from lignin chlorination and oxidation. Color removal from the effluent by hydrogen peroxide at neutral pH was catalyzed by addition of horseradish peroxidase. The catalysis with peroxidase (20 mg/L) was observed over a wide range of peroxide concentrations (0.1mM–500mM), but the largest effect was between 1mM and 100mM. The pH optimum for catalysis was around 5.0, while the basal rate of noncatalyzed peroxide color removal simply increased with pH within the range tested (3–10). Peroxidase catalysis at pH 7.6 reached a maximum at 40°C in 4 h assays with 10mM peroxide, and disappeared above 60°C. Compared with mycelial color removal by Coriolus versicolor, the rate of color removal by peroxide plus peroxidase was initially faster (first 4 h), but the extent of color removal after 48 h was higher with the fungal treatment. Further addition of peroxidase to the enzyme‐treated effluent did not produce additional catalysis. Thus, the peroxide/peroxidase system did not fully represent the metabolic route used by the fungus.
A dynamic mathematical model for microbial removal of pyritic sulfur from coal
Authors: Kargi Fikret , Weissman Jeffrey G.
Published: December 2004

A dynamic mathematical model has been developed to describe microbial desulfurization of coal by Thiobacillus ferrooxidans. The model considers adsorption and desorption of cells on coal particles and microbial oxidation of pyritic sulfur on particle surfaces. The influence of certain parameters, such as microbial growth rate constants, adsorption‐descrption constants, pulp density, coal particle size, initial cell and solid phase substrate concentration on the maximum rate of pyritic sulfur removal, have been elucidated. The maximum rate of pyritic sulfur removal was strongly dependent upon the number of attached cells per coal particle. At sufficiently high initial cell concentrations, the surfaces of coal particles are nearly saturated by the cells and the maximum leaching rate is limited either by total external surface area of coal particles or by the concentration of pyritic sulfur in the coal phase. The maximum volumetric rate of pyritic sulfur removal (mg S/h cm3 mixture) increases with the pulp density of coal and reaches a saturation level at high pulp densities (e.g. 45%). The maximum rate also increases with decreasing particle diameter in a hyperbolic form. Increases in adsorption coefficient or decreases in the desorption coefficient also result in considerable improvements in this rate. The model can be applied to other systems consisting of suspended solid substrate particles in liquid medium with microbial oxidation occurring on the particle surfaces (e.g., bacterial ore leaching). The results obtained from this model are in good agreement with published experimental data on microbial desulfurization of coal and bacterial ore leaching.
Utilization of light for the assimilation of organic matter in Chlorella sp. VJ79
Authors: Lalucat J. , Imperial J. , Parés R.
Published: December 2004

Chlorella sp. strain VJ79 was isolated from a total heterotrophic count of a wastewater collector. It grows autotrophically, heterotrophically, and mixotrophically on a variety of organic substrates. Glucose and serine promote a mixotrophic growth from which the yield is higher than the sum of autotrophic and heterotrophic yields, but serine assimilation requires light. The interaction of glucose and light was studied in proliferating and nonproliferating cells by respirometry (IRGA and Warburg) and growth experiments. Glucose inhibits the photosynthetic CO2 fixation ten‐fold and modifies the pigmentary system as it does in heterotrophic cultures. Light inhibits glucose uptake and assimilation, but under mixotrophic conditions maximal utilization of glucose is obtained. Mutants defective in autotrophic growth were isolated by mutagenesis with nitrosoguanidine. They show a degenerated pigmentary system and a mixotrophic growth yield equal to that of the heterotrophic growth. The analysis of the mixotrophic system shows that light energy, dissipated during autotrophic growth, is used under mixotrophic conditions. From the increase in growth, the increase in photosynthetic efficiency can be calculated as ca. sixfold.
Mechanical control of foaming in a bubble column
Authors: Ohkawa Akira , Sakai Nobuyuki , Imai Hiroshi , Endoh Kazuo
Published: December 2004

This study was performed to evaluate the effects of the air sparge rate, working liquid volume, liquid feed rate onto the disk, and disk diameter on the foam‐breaking performance of foam‐breaking apparatus with a rotating disk (FARD) installed in the bubble column. Experimental results showed that the smaller the air sparge rate and working liquid volume were, and the larger the liquid feed rate and disk diameter, the lower the critical disk rotational speed required for reduced foam‐breaking. The presence of the effective ranges of the disk diameter and liquid feed rate for foam breaking was also confirmed. Furthermore, the quantitative predictions of the upper limits of the liquid feed rate, foam‐breaking regions, and the required foam‐breaking power were carried out, based on the results obtained above. Comparison of the FARD with two conventional mechanical foam‐breaking spray‐type apparati also demonstrated the highest level of the FARD in respect not only to foam‐breaking performance but also to power requirements.
Detection of microscopic leaks in fermenter cooling coils
Authors: Perkowski C. A. , Daransky G. R. , Williams J.
Published: December 2004

Microscopic leaks in fermenter cooling coils were identified as the source of chronic fermentation contaminations. Methods used to identify the problem in production fermenters are described. Recommendations for upgrading quality control criteria for new installations are presented.
Application of a statistical procedure for the control of yeast production
Authors: Kishimoto Michimasa , Sawano Toshihiro , Yoshida Toshiomi , Taguchi Hisaharu
Published: December 2004

In many cases of fermentation processes, it is difficult to measure all of the state variables needed to indicate the culture state and to predict state changes. We propose the use of time‐series data of measurable state variables instead of unmeasurable to describe the fermenatation process. We also employ a discrimination method of independent variables of regression analysis using statistical measures, PSS and AIC. These statistical procedure were applied to fed batch culture for yeast production under aerobic conditions, and the effectiveness was ascertained experimentally.
Enzyme immobilization in porous solid supports—penetration of immobilized enzyme
Authors: Do D. D.
Published: December 2004

The process of enzyme immobilization under the diffusion‐controlled regime (i.e., fast attachment of enzyme compared to its diffusion) is modeled and theoretically solved in this article. Simple and compact solutions for the penetration depth of immobilized enzyme and the bulk enzyme concentration versus time are presented. Furthermore, the conditions for the validity of our solutions are also given in this article so that researchers can discover when the theoretical solutions can be applied to their systems.
Hydrolysis of wheat straw hemicellulose with trifluoroacetic acid. Fermentation of xylose with Pachysolen tannophilus
Authors: Fanta G. F. , Abbott T. P. , Herman A. I. , Burr R. C. , Doane W. M.
Published: December 2004

Treatment of wheat straw with 1N trifluoroacetic acid (TFA) for 7 h at reflux temperature yielded 23% xylose based upon initial straw weight. This corresponds to about an 80% xylose yield based on the xylan content of the hemicellulose. The cellulose component of wheat straw was largely unaffected, as evidenced by low glucose yields. Decomposition of xylose by prolonged refluxing (23 h) was minimal in 1N TFA compared to 1N HCl. Treatment of wheat straw with refluxing 1N TFA converts about 10% of the lignin initially present in straw into water‐soluble lignin fragments. Fermentation of the xylose‐rich wheat straw hydrolyzate to ethanol with Pachysolen tannophilus was comparable to the fermentation of reagent grade xylose, indicating that furfural and toxic lignin by‐products were not produced by 1N TFA in sufficient amounts to impair cell growth and ethanol production. Cellulase treatment of the wheat straw residue after TFA hydrolysis resulted in a 70–75% conversion of the cellulose into glucose.
Peptide synthesis in aqueous–organic solvent mixtures with α‐chymotrypsin immobilized to tresyl chloride‐activated agarose
Authors: Nilsson Kurt , Mosbach Klaus
Published: December 2004

α–Chymotrypsin was immobilized with a high coupling yield (up to 80%) to tresyl chloride activated Sepharose CL‐4B.The immobilized enzyme was tested for its ability to synthesize soluble peptides from N‐acetylated amino acid esters as acyl donors and amino acid amides as acceptor amines in water–water‐miscible organic solvent mixtures. It was found that the yield of peptide increased with increasing concentration of organic cosolvent. Almost complete synthesis (97%) of Ac–Phe–Ala–NH2 was obtained from Ac–Phe–OMe using a sixfold excess of Ala–NH2. The rate of peptide formation in aqueous–organic solvent mixtures was good. Thus, 0.1M peptide was formed in less than 2 h in 50 vol% DMF with 0.1 mg immobilized chymotrypsin/mL reaction mixture. The immobilized enzyme distinguished between the L and D configurations of acceptor amino acid amides even in high concentration of nonaqueous component (90% 1,4‐butanediol). The effect of temperature was studied. It was found that both the yield of peptide and the stability of immobilized enzyme increased when the temperature was lowered. Experiments could be performed at subzero temperatures in the aqueous–organic solvent mixtures resulting in very high yield of peptide. After three weeks continuous operation at 4°C in 50% DMF, the immobilized enzyme retained 66%of its original synthetic activity. The activity of the immobilized enzyme was better conserved with a preparation made from agarose with a higher tresyl group content compared to a preparation made from a lower activated agarose, indicating that multiple point of attachment has a favorable effect on the stability of the enzyme in aqueous–organic solvent mixtures. The major advantage of using water‐miscible instead of water‐immiscible organic solvents to promote peptide syntheses appears to be the increased solubility of substrates and products, making continuous operation possible.
Feed component inhibition in ethanolic fermentation by Saccharomyces cerevisiae
Authors: Maiorella B. L. , Blanch H. W. , Wilke C. R.
Published: December 2004

Inhibition by secondary feed components can limit productivity and restrict process options for the production of ethanol by fermentation. New fermentation processes (such as vacuum or extractive fermentation), while selectively removing ethanol, can concentrate nonmetabolized feed components in the remaining broth. Stillage recycle to reduce stillage waste treatment results in the buildup of nonmetabolized feed components. Continuous culture experiments are presented establishing an inhibition order: CaCl2, (NH4)2×SO4 > NaCl, NH4Cl > KH2PO4 > xylose, MgCl2 > MgSO4 > KCl. Reduction of the water activity alone is not an adequate predictor of the variation in inhibitory concentration among the different components tested. As a general trend, specific ethanol productivity increases and cell production decreases as inhibitors are added at higher concentration. We postulate that these results can be interpreted in terms of an increase in energy requirements for cell maintenance under hypertonic (stressed) conditions. Ion and carbohydrate transport and specific toxic effects are reviewed as they relate to the postulated inhibition mechanism. Glycerol production increases under hypertonic conditions and glycerol is postulated to function as a nontoxic osmoregulator. Calcium was the most inhibitory component tested, causing an 80%decline in cell mass production at 0.23 mol Ca2+/L and calcium is present at substantial concentration in many carbohydrate sources. For a typical final cane molasses feed, stillage recycle must be limited to less than onethird of the feed rate; otherwise inhibitory effects will be observed.
Studies on on‐line bioreactor identification. I. Theory
Authors: Stephanopoulos Gregory , San Ka‐Yiu
Published: December 2004

An integrated approach is presented for the on‐line estimation of the state of a biochemical reactor from presently attainable real‐time measurements. Elemental and macroscopic balances are used for the determination of the total rate of growth and state‐of‐the‐art estimation techniques are subsequently employed for the elimination of process and measurement noises and the estimation of state variables and unknown culture parameters. The proposed approach is very flexible in that as new sensors become available they can be easily incorporated within the present framework to estimate new variables or improve the accuray of the old ones. The method does not require any model for the growth kinetics and is very successful in accurately estimating the above variables in the presence of intense noise and under both steady‐state and transient conditions. State estimates obtained by the presented method can be used for the development of adaptive optimal control schemes as well as for basic studies of the characteristic properties of microbial cultures.
Studies on on‐line bioreactor identification. IV. Utilization of pH measurements for product estimation
Authors: San Ka‐Yiu , Stephanopoulos Gregory
Published: December 2004

Relationships between the total rate of biomass growth and the rate of ammonia addition to a fermentor for pH control are presented. These equations make use of the concept of reaction invariants and provide the additional information needed for bioreactor identification. They are especially useful when the RQ measurement is not sufficient for this purpose, such as when sensitivities arise with the measured values of the respiratory quotient or when fermentation products are formed. The cases of batch, fed‐batch and continuous fermentations, forming products with or without acidic/basic properties are considered. The derived relationships were successfully tested with nonbiological acid‐base continuous flow reaction systems and subsequently applied to the identification of the continuous yeast fermentation of glucose to ethanol. Results of these experimental studies are also presented.
Invertase immobilization via its carbohydrate moiety
Authors: Marek M. , Valentová O. , Káš J.
Published: December 2004

After periodate oxidation of its glycosidic component, invertase was covalently bound onto three types of modified solid supports: glycidyl methacrylate, styrene–divinylbenzene copolymers, and bead cellulose. Direct reaction of the invertase aldehyde groups that were formed with amino groups of the support and use of the modified Ugi reaction have been employed as immobilization procedures. Apart from binding methods, the important effects of the buffer, support, conditions of periodate oxidation, and the length of the spacer on the activity of the enzyme conjugate have been investigated. Superior conjugate activity was obtained, via modified Ugi reaction, by the immobilization of a suitably oxidized invertase to a styrene–divinylbenzene copolymer having free amino groups.
Ease of removal of barnacles from various polymeric materials
Authors: Becka Ann , Loeb George
Published: December 2004

The forces required to remove living, fully attached barnacles from the surface of a number of polymeric solids were measured. The forces were related to the surface energy components of the materials. The results indicate a positive correlation between polymer surface energy and force required for barnacle removal. The nonpolar component of the surface energy was more closely related to the removal force than the polar component, although the polar component is significant. Adherence to some composite materials was greater than was consistent with the correlation for noncomposites.
Mixed populations of marine microalgae in continuous culture: Factors affecting species dominance and biomass productivity
Authors: Regan D. L. , Ivancic N.
Published: December 2004

Marine microalgae were grown in multispecies continuous cultures. Under carbon dioxide limitation, blue–green algae dominated. Under nitrate and light limitation, species dominance depended on the initial conditions. When the inoculum consisted primarily of blue–green algae with smaller amounts of other species, blue–green algae and pennate diatoms dominated. When the inoculum consisted of equal amounts of all species, green flagellates and pennate diatoms dominated. Green flagellates and blue–green algae were incompatible and never shared dominance. When nutrient limitations were overcome, the productivity of seawater was increased 100‐fold before light limitation occurred. The productivity could be further increased by reducing photorespiration in the culture. The dilution rates studied (0.1, 0.2, and 0.4 day−1) had no effect on species dominance, nor did the higher dilution rates select for smaller cells. The maximum productivity occurred at a dilution rate of 0.2 day−1. Temperature had the greatest effect on species dominance, with green flagellates, pennate diatoms, and blue–green algae dominating at 20°C and only blue–green algae dominating at 35°C. The productivity at 35°C was lower than that at 20°C because of the lower solubility of carbon dioxide at higher temperatures. At 10% salinity, green flagellates and pennate diatoms dominated. The productivity at this salinity was 50% that obtained at the salinity of seawater (3.5%). At 25% salinity, only the green flagellate, Dunaliella salina, survived at a productivity of 1% that obtained at the salinity of seawater.
Cybernetic modeling of microbial growth on multiple substrates
Authors: Kompala Dhinakar S. , Ramkrishna Doraiswami , Tsao George T.
Published: December 2004

The internal regulatory processes, which underlie a variety of behavior in microbial growth on multiple substrates, are viewed as a manifestation of an invariant strategy to optimize some goal of the cells. A goal‐seeking or cybernetic model is proposed here, with the optimization obased on a short‐term perspective of response to the environment. The model parameters are determined from the growth data on single substrates. The model predicts the entire range of microbial growth behavior on multiple substrates from simultaneous utilization of all sugars to sequential utilization with pronounced diauxic lags. It is shown to predict the many variations of the diauxic phenomenon in different growth conditions. The transients in continuous culture growth on mixed substrates caused by varying the feed strategies are easily simulated by this model. The framework of this model can be applied to batch or continuous culture growth of many bacteria on different combinations of substrates.
Thermal stabilization of amylolytic enzymes by covalent coupling to soluble polysaccharides
Authors: Lenders J.‐P. , Crichton R. R.
Published: December 2004

The immobilization of pullulanase and β‐amylase on soluble polysaccharides (dextrans and amylose) has been carried out. The method used for coupling the enzymes to the carbohydrate support involves limited periodate oxidation of the polysaccharide followed by reductive alkylation with sodium cyanoborohydride or borohydride. The influence of the degree of functionalization of the carbohydrate, the incubation time, the nature of the reducing agent and, for the dextrans studied, their molecular weight, on the properties of the conjugate were studied. We have observed an apparent correlation between the molecular weight of the glycoprotein conjugates formed and their thermal stability, resistance to urea denaturation and their kinetic parameters. By selecting the proper experimental conditions leading to conjugates with maximum thermal stabilities, it has also been shown that β‐amylase conjugates can hydrolyze starch at a temperature 20°C higher than the corresponding value for the native enzyme. This result demonstrates that conjugation may result in modified enzymes leaving a high operational stability at elevated temperatures. We suggest that the immobilization method presented in this article represents an approach to the stabilization of enzymes employed at an industrial level, which may be of general application.
A cybernetic view of microbial growth: Modeling of cells as optimal strategists
Authors: Dhurjati P. , Ramkrishna D. , Flickinger M. C. , Tsao G. T.
Published: December 2004

A cybernetic framework is presented which views microbial response in multiple substrate environments as a judicious investment of cellular resources in synthesizing different key proteins according to an optimal regulatory strategy. A mathematical model is developed within the cybernetic framework for the diauxic growth of Klebsiella pneumoniae on a mixture of D‐glucose and D‐xylose. The “bang–bang” optimal policy describes well the experimental observations obtained using a fermenter coupled to an Apple II microcomputer. Striking variations in respiratory levels are observed experimentally during the switching of the cell's adaptive machinery for the utilization of the less preferred substrate.
Solid‐state fermentation of sweet sorghum to ethanol
Authors: Kargi Fikret , Curme James A. , Sheehan John J.
Published: December 2004

Solid‐state fermentation of chopped sweet sorghum particles to ethanol was studied in static flasks using an ethanol tolerant yeast strain. The influence of various process parameters, such as temperature, yeast cell concentration, and moisture content, on the rate and extent of ethanol fermentation was investigated. Optimal values of these parameters were found to be 35°C, 7 × 108 cells/g raw sorghum, and 70% moisture level, respectively.
Enzymatic gallic acid esterification
Authors: Weetal Howard H.
Published: December 2004

Gallic acid esters of n‐propyl and amyl alcohols have been produced by enzymatic synthesis in organic solvents using immobilized tannase. Studies indicate that maximum esterification of gallic acid occurs with amyl alcohol. The enzyme shows broad alcohol specificity. However, the enzyme exhibits absolute specificity for the acid portion of the ester. Studies were carried out on Km, Vmax, pH, and temperature optima.
Enzymatic hydrolysis and recrystallization behavior of initially amorphous cellulose
Authors: Bertran Maria Silvia , Dale Bruce E.
Published: December 2004

Cellulose samples from cotton and wood pulps with varying low degrees of crystallinity (mechanically decrystallized) were studied. The influence of initial cellulose crystallinity on sugar yield after enzymatic hydrolysis was determined by two different methods. As expected, samples with low crystallinity were much more accessible to enzymatic attack and glucose yields were higher than were samples of high initial crystallinity. Hydrolysis of cellulose seems more dependent on cellulose crystallinity than on the source of cellulose. It is known that decrystallized or amorphous cellulose can recrystallize under proper conditions, e.g., during acid hydrolysis. The data reported here also reveal some recrystallization during enzymatic hydrolysis which probably occurs simulataneously with a selective enzymatic attack on the amorphous regions of cellulose. In all cases, the amorphous celluloses recrystallized in the original lattice form, that of native cellulose.
Application of the upflow anaerobic sludge bed (UASB) process for treatment of complex wastewaters at low temperatures
Authors: Koster I. W. , Lettinga G.
Published: December 2004

The feasibility of the upflow anaerobic sludge bed (UASB) process for the treatment of potato starch wastewater at low ambient temperatures was demonstrated by operating two 5.65‐L reactors at 14°C and 20°C, respectively. The organic space loading rates achieved in these laboratory‐scale reactors were 3 kg COD/m3/day at 14°C and 4‐5 kg COD/m3/day at 20°C. The corresponding sludge loading rates were 0.12 kg COD/kg VSS/day at 14°C and 0.16−0.18 kg COD/kg VSS/day at 20°C.

These findings are of considerable practical importance because application of anaerobic treatment at low ambient temperatures will lead to considerable savings in energy needed for operating the process. As compared with various other anaerobic wastewater treatment processes, a granular sludge upflow process represents one of the best options developed so far. Although the overall sludge yield under psychrophilic conditions is slightly higher than under optimal mesophilic conditions, this doesn't seriously hamper the operation of the process. The extra sludge yield, due to accumulation of slowly hydrolyzing substrate ingredients, was 4.75% of the COD input at 14°C and 1.22% of the COD input at 20°C.
Feasible and optimal retrofitting of batch‐soluble to continuous‐immobilized enzyme processes applied to adsorbed enzymes
Authors: Domach M. M. , Gricus T. J.
Published: December 2004

The advantages of retrofitting an in situ soluble enzyme batch process to an immobilized enzyme continuous process are contrasted against the disadvantages by means of a dimensionless feasibility/optimization analysis. The general analysis is applied to the case of an adsorbed enzyme system where a maximum in activity occurs with respect to loading. For this case, a minimum in the ratio of enzyme‐carrier complex working lifetime to in situ batch process time and a maximum in the cost difference between the in situ and retrofit processes occurs with respect to loading and retrofit process conversion. For the maximization of cost difference, the analysis also suggests a criterion that can be used to determine whether the values for optimal loading and retrofit conversion will result in the retrofit being economically feasible. When infeasibility occurs, qualitative sensitivity analysis for a variety of situations points out whether a catalyst or process modification will improve feasibility the most. Apart from forming the basis for an iterative retrofit process design algorithm, the modeling approach's ability to specify optimal values of catalyst properties such as loading lends itself to defining process‐specific, catalyst design “targets” would be useful for those developing immobilized enzyme preparation methodology and those investigating enzyme–carrier interactions.
Structure and properties of enzyme graft copolymers: Temperature effects on HRP immobilization mechanism
Authors: D'Angiuro L. , de Lalla C. , Cremonesi P.
Published: December 2004

The possibility of obtaining immobilized horseradish peroxidase (HRP) materials with K′m values close to that of the native enzyme, but with good thermal stability, was investigated. The photochemical reaction was used as the immobilization methodology. Temperature and catalyst concentration were found to be the main parameters able to control the immobilization reaction mechanism more than type of functional monomer, polymer–matrix, and enzyme–polymer ratios. By carrying out the immobilization reaction at 35°C and using either bisacryloylpiperazine (BAP) or hexhydro‐1,3,5‐triacryloyl‐s‐triazine (HTsT) as the functional monomer, materials with a good thermal stabilization (the retained activity after 240 min at 60°C was between 65–25%) as well as kinetic constants (0.6–0.8 × 10−4M) similar to that of the free enzyme (0.57 × 10−4M) were obtained. Since low K′m values were obtained also using a high polymer content (pBAP copolymers, 25%; pHTsT copolymers, 30%) and neither limitation to substrate diffusion nor a reduction of the enzyme mobility was found, the enzyme should be linked to the matrix during the last steps of monomer polymerization, and it should have an external disposition with respect to the support.
Heterogeneous denaturation of enzymes: A distributed activation energy model with nonuniform activities
Authors: Agarwal Pradeep Kumar
Published: December 2004

A model is proposed for the denaturation of enzymes based on heterogeneous enzyme subpopulations with nonuniform initial activities and nonzero final activities. The more frequently used simple first‐order deactivation model is a special case of the model corresponding to the standard deviation of Gaussian distribution of activation energies approaching zero. Parametric studies made with the model are capable of simulating the reported trends in experimental data on the thermal profile and activity time behavior of native as well as modified enzymes with a minimum number of adjustable parameters. The model predictions are found to be in good agreement with data reported in the literature.
Steric hindrance of growth of filamentous fungi in solid substrate fermentation of wheat straw
Authors: Laukevics J. J. , Apsite A. F. , Viesturs U. S. , Tengerdy R. P.
Published: December 2004

Cellulolytic fungi, such as Trichoderma reesei, T. lignorum, and Chaetomium cellulolyticum reach a low packing density of mycelia when grown on straw under conditions of solid substrate fermentation. The low packing density is shown to be caused partially by the geometric limitation of the growth of mycelia in the substrate and particularly in its pores, but the exact contribution of this limitation and other limitations such as mass transfer and substrate availability cannot be easily distinguished. The combined effect of such limitations is called steric hindrance. This steric hindrance is associated with and may be the principal cause of low biomass concentration in SSF.
Ion exchange process for removing glucosyltransferase from crude glucoamylase
Authors: Ayers J. S.
Published: December 2004

The advant of a new range of high‐protein capacity cellulosic ion exchangers suitable for use on an industrial scale made it worthwhile investigating the conditions necessary to remove the contaminating enzyme glucosyltransferase from a commercial preparation of crude glucoamylase. The potential of the SP derivative, SP Indion®, for achieving this separation is shown. At pH 2.5 the glucosyltransferase was selectively adsorbed by the ion exchanger, and 99% of the glucoamylase was recovered in the eluate from the column. Purification of an Aspergillus culture filtrate by this method will require careful control of the ionic strength of the culture medium if it is to be used without the additional step of cation exchange to lower than pH to 2.5.
Stability of alginate‐immobilized algal cells
Authors: Dainty A. L. , Goulding K. H. , Robinson P. K. , Simpkins I. , Trevan M. D.
Published: December 2004

Investigations were carried out using immobilized Chlorella cells to determine the diameter, compressibility, tolerance to phosphate chelation, and ability to retain algal cells during incubation of various alginate beads. These physical bead characteristics were found to be affected by a variety of interactive factors, including multivalent cation type (hardening agent) and cell, cation, and alginate concentration, the latter exhibiting a predominant influence. The susceptibility of alginate beads to phosphate chelation was found to involve a complex interaction of cation type, concentration, and pH of phosphate solution. A scale of response ranging from gel swelling to gel shrinking was observed for a range of conditions. However, stable calcium alginate beads were maintained in incubation media with a pH of 5.5 and a phosphate concentration of 5μM. A preliminary investigation into cell leakage from the beads illustrated the importance of maintaining a stable gel structure and limiting cell growth to reduce leakage.
Dilute acid hydrolysis of wheat straw hemicellulose at moderate temperature: A simplified kinetic model
Authors: González G. , López‐Santín J. , Caminal G. , Solà C.
Published: December 2004

Wheat straw has been hydrolized with sulfuric acid at 34 and 90°C. The treatment at 90°C yields complete solubilization of hemicellulose to xylose and arabinose without significant amounts of furfural. The influence of acid concentration was studied and the kinetics of the acid‐catalyzed hydrolysis has been modeled suggesting a two‐consecutive reactions mechanism. This model is useful to explain the different behavior of the concentration of the two main sugars produced. The enhanced cellulose accessibility to enzymatic attack is also reported.
Growth of animal cells on microbeads. I. In situ estimation of numbers
Authors: Miller S. J. O. , Henrotte M. , Miller A. O. A.
Published: December 2004

Evaluation of the number of anchorage‐dependent cells growing on the surface of microbeads kept in suspension in a bioreactor is a tedious procedure fraught with many difficulties. Using the Coulter counter as a biomass probe, this article shows that the number of cells adhering to microbeads can be determined while the cells are still attached.
Role of exocellular polymer in the design of activated sludge
Authors: Sheintuch M. , Lev O. , Einav P. , Rubin E.
Published: December 2004

This research is aimed at understanding the reactor‐settler interaction. The reactor operating conditions affect the sludge‐settling properties due to (a) production of exocellular polymer that serves as a flocculant in the settler and (b) population shift from flocculating bacteria to filamentous microorganisms that do not settle. A structured kinetic model that accounts for stored substrate and production of polymers, biomass, and inerts was constructed and applied to various open and closed reactor configurations. It is based on our observation that, in a batch reactor, the polymer is produced during endogenous respiration. The model describes well the observed temporal variation in substrate, biomass, and polymer concentration. Application of the model to continuous operation predicts increasing polymer concentration with sludge age, which is in good agreement with one study in the literature. Our study in a once‐through reactor, as well as others, suggests an inverse dependence. The difference is probably due to different operating modes. Our study confirmed the role of the polymer in the sedimentation process. Under some conditions, however, a slow population shift to filamentous growth becomes the dominant factor.
Encapsulation of viable cells within polyacrylate membranes
Authors: Gharapetian H. , Davies N. A. , Sun A. M.
Published: December 2004

A new, semipermeable hydrogel membrane for encapsulating viable cells has been developed. The encapsulation was performed by consecutively introducing droplets of a suspension of hybridoma cells in a solution of a polyanionic acrylic copolymer into aqueous solutions of three polycationic polymers. As a result of interpolymeric ionic interactions and some chemical reactions, a polyelectrolyte complex membrane was formed at the interface between each droplet and the polycationic polymeric solutions. The hybridoma cells, used as a model system, were derived by fusing spleen cells from immunized BALB/c mice with the NS‐1 murine plasmacytoma cell line. The cells divided and gradually filled the microcapsules over a period of 8 days. Prior to encapsulation of the hybridoma cells, the polyanions were tested for toxicity and inhibition of cell growth. A direct relationship was observed between hybridoma cell viability in the acrylic polyanion/RPMI‐1640/10% (w/v) fetal calf serum (FCS) solutions and the kinematic viscosities of the solutions of the polyanions. Antihuman IgM was produced by the encapsulated hybridoma cells and immunoassay showed that the antibody concentration was 3 μg/ml of the total culture medium.
Quantitative method based on energy and mass balance for estimating substrate transient accumulation in activated sludge during wastewater treatment
Authors: Guiot S. R. , Nyns E. J.
Published: December 2004

To calculate the transient accumulation of soluble organic matter in activated sludge, an equation based on COD and respirometry is described. In this approach the difference between the actual utilized organic matter and the metabolized matter is expressed as substrate transient accumulation. The amount of substrate generated by the lysis of dead microorganisms was taken into account, and the metabolized organic matter was expressed in two main endergonic functions of O2 consumption, that is, assimilation and maintenance. The equation thus derived was simplified to contain parameters such as COD and O2 consumption and tested on experimental results. The results show that the values obtained using this equation compared well to substrate removal in the absence of O2 in short‐term batch cultures.