Biomedical subjects

G Zacchi

Publications and source records attributed to G Zacchi.

24 records · Page 2Linked to original sources

PubMed1995

MIST: a user-friendly metabolic simulator.

The Metabolic Interactive Simulation Tool, MIST, is a software package, running under Microsoft Windows 3.1, which can be used for dynamic simulations, stoichiometric calculations and control analysis of metabolic pathways. The pathways can be of any complexity and are defined by the user in a simple, interactive way. The user-defined enzymatic rate equations can be compiled either by an external or an internal compiler. Simulations of pathways compiled by an external compiler run significantly faster, but since these compilers are commercial software, they are not distributed together with MIST. The simulations are performed by numerical integration of a set of ordinary differential equations. The integration can be done by either an explicit fourth-order Runge-Kutta algorithm or a semi-implicit third-order Runge-Kutta algorithm, both with adjustable step size. The second algorithm can be used if the set of differential equations is stiff. Vector-based drawing facilities are included in the program, with which results can be presented in graphs. Results of simulations, including graphics, can be stored in files. MIST is a very user-friendly, flexible and yet powerful program, with the mathematical details regarding models, simulations and calculations hidden from the user. This makes it suitable for scientists and students with limited computer experience.

Algorithms↗

PubMed1991

Simulation of batch and continuous reactors with co-immobilized yeast and beta-galactosidase.

A reaction-diffusion model was used to simulate a co-immobilized system utilizing the numerical method of orthogonal collocation. The production of ethanol from deproteinized whey using beta-galactosidase co-immobilized with Saccharomyces cerevisiae in calcium alginate gel beads was chosen as a model system. Calculated concentrations of lactose, glucose, galactose and ethanol were compared with experimental data for a batch reactor and a continuous horizontal packed-bed reactor. The mathematical model has been used to analyse the influence of internal and external mass transfer for the continuous reactor. The external mass transfer was shown to be of minor importance. The introduction of baffles decreased the backmixing in the horizontal packed-bed reactor. Internal mass transfer was found to be the main cause of the reduction in the apparent reaction rate. Thus, much of the expected increase in reaction rate is diminished by mass transfer hindrance when the cell concentration is increased.

Alginates↗

PubMedDate not supplied

Influence of enzyme loading and physical parameters on the enzymatic hydrolysis of steam-pretreated softwood.

Softwood is an interesting raw material for the production of fuel ethanol as a result of its high content of hexoses, and it has attracted attention especially in the Northern hemisphere. However, the enzymatic hydrolysis of softwood is not sufficiently efficient for the complete conversion of cellulose to glucose. Since an improvement in the glucose yield is of great importance for the overall economy of the process, the influence of various parameters on the cellulose conversion of steam-pretreated spruce has been investigated. The addition of beta-glucosidase up to 50 IU g(-)(1) cellulose to the enzymatic hydrolysis process resulted in increased cellulose conversion at a cellulase loading up to 48 FPU g(-)(1) cellulose. Despite very high enzyme loading (120 FPU g(-)(1) cellulose) only about 50% of the cellulose in steam-pretreated spruce was converted to glucose when all of the material following pretreatment was used in the hydrolysis step. The influence of temperature, residence time, and pH were investigated for washed pretreated spruce at a dry matter (DM) content of 5% and a cellulase activity of 18.5 FPU g(-)(1) cellulose. The optimal temperature was found to be dependent on both residence time and pH, and the maximum degree of cellulose conversion, 69.2%, was obtained at 38 degrees C and pH 4.9 for a residence time of 144 h. However, when the substrate concentration was changed from 5% to 2% DM, the cellulose conversion increased to 79.7%. An increase from 5% to 10% DM resulted, however, in a similar degree of cellulose conversion, despite a significant increase in the glucose concentration from 23 g L(-)(1) to 45 g L(-)(1). The deactivation of beta-glucosidase increased with increasing residence time and was more pronounced with vigorous agitation.

Aspergillus↗

PubMedDate not supplied

Measurement of diffusion coefficients in gels using holographic laser interferometry.

The accuracy and precision of holographic interferometry as a method to measure diffusion coefficients in gels are investigated both experimentally and theoretically. The standard deviations in the experimentally determined diffusion coefficient for ethanol in 4% (w/v) agarose gel were 3.3% for diffusion into the gel and 6.1% for diffusion out of the gel. These are in good agreement with the standard deviations obtained using Monte Carlo simulations. Systematic errors derived from an assumption of constant diffusion coefficients were also investigated.

Computer Simulation↗

PubMedDate not supplied

Cost analysis of ethanol production from willow using recombinant Escherichia coli.

This study comprises a technical and economic analysis of the production of fuel ethanol by fermentation of a pentose-rich hydrolysate with recombinant Escherichia coli, strain KO11. Hydrolysate from steam-pretreated willow was used as raw material in calculations regarding the fermentation. The calculations were based on a feed capacity of 10 metric tons of dry willow per hour to the pretreatment stage, providing 35 metric tons of hydrolysate per hour, consisting of 45 g of sugars/L, to the pentose fermentation plant. A detoxification step was included, since the hydrolysate has been shown to have an inhibitory effect on the E. coli KO11. The technical data used in the calculations were based on a kinetic fermentation model, which was developed from laboratory-scale experiments in a previous study. The economic analysis predicted an ethanol production cost of 48/L in the pentose fermentation plant, indicating potentially good economy. The detoxification cost constitutes 22% of this cost. Sensitivity analyses revealed that if the concentration of sugars in the feed to the fermentation was decreased by 40% to 27 g/L, the ethanol production cost was increased to 54/L. The production cost was increased to 50/L ethanol if the cell mass was recirculated to the fermentation stage 5 times instead of 20.

Biotechnology↗

PubMedDate not supplied

[Enzymatic hydrolysis of willow treated with a steam burst without preliminary water extraction with a high concentration of substrate].

A laboratory reactor equipped with a screw press was used for hydrolysis of steam-SO2 exploded willow Salix caprea by a composition of Trichoderma reesei and Aspergillus foetidus enzyme preparations at high substrate concentrations. Optimal conditions providing the maximal volume of hydrolysis syrup with maximal sugar concentrations were determined. Two different hydrolysis procedures were developed in order to exclude initial washing of steam-pretreated plant raw material by large volumes of water, which is necessary to eliminate the inhibitory effect of explosion by-products on enzymatic hydrolysis. The first procedure included a one-hour-long enzymatic prehydrolysis of the substrate, then separation of sugar syrup containing 40-60 g/l of glucose, 20-25 g/l of xylose, and up to 10% of disaccharides, as well as up to 35% of the initial enzymatic activity, then addition of a diluted acetate buffer (pH 4.5), and subsequent hydrolysis of the substrate by the adsorbed enzymes leading to the final accumulation of up to 140 g/l glucose and up to 15 g/l xylose. In the second scenario, the exploded willow was initially adjusted by alkali to pH 4.5 and then hydrolyzed directly by added enzymes for 24 hours. This procedure resulted in a nearly total polysaccharide hydrolysis and accumulation of up to 170 g/l glucose and 20 g/l xylose. The reasons of inhibition of enzymatic hydrolysis are discussed.

Aspergillus↗