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G Zacchi

Publications and source records attributed to G Zacchi.

At least 19 recordsLinked to original sources
PubMed2006

Bio-ethanol--the fuel of tomorrow from the residues of today.

The increased concern for the security of the oil supply and the negative impact of fossil fuels on the environment, particularly greenhouse gas emissions, has put pressure on society to find renewable fuel alternatives. The most common renewable fuel today is ethanol produced from sugar or grain (starch); however, this raw material base will not be sufficient. Consequently, future large-scale use of ethanol will most certainly have to be based on production from lignocellulosic materials. This review gives an overview of the new technologies required and the advances achieved in recent years to bring lignocellulosic ethanol towards industrial production. One of the major challenges is to optimize the integration of process engineering, fermentation technology, enzyme engineering and metabolic engineering.

Agriculture↗
PubMed2002

A review of the production of ethanol from softwood.

Ethanol produced from various lignocellulosic materials such as wood, agricultural and forest residues has the potential to be a valuable substitute for, or complement to, gasoline. One of the major resources in the Northern hemisphere is softwood. This paper reviews the current status of the technology for ethanol production from softwood, with focus on hemicellulose and cellulose hydrolysis, which is the major problem in the overall process. Other issues of importance, e.g. overall process configurations and process economics are also considered.

Cellulose↗
PubMed2001

The effect of shaking regime on the rate and extent of enzymatic hydrolysis of cellulose.

In an attempt to elucidate the effect of mixing on the rate and extent of enzymatic hydrolysis of cellulosic substrates, alpha-cellulose was hydrolysed using a commercial cellulase preparation at varying levels of substrate concentration (2.5,5 and 7.5% (w/v)) and by using three shaking regimes: continuous at low-speed (25 rpm), continuous at high-speed (150 rpm) and an intermittent regime comprised of high and low-speed shaking intervals. The continuous, high-speed shaking produced the highest conversion yields, whereas the intermittent and low-speed shaking regimes resulted in lower conversions. After 72 h, at all shaking regimes (150 rpm,25 rpm and intermittent), using a low substrate concentration (2.5%) produced conversion yields (82,79 and 80%) higher than those obtained at high (7.5%) substrate concentration (68,63 and 68%). As the substrate concentration increased, the conversion yields at intermittent shaking gradually approached those resulting from high-speed shaking. Thus, it appears that intermittent shaking could be a beneficial process option as it can reduce the mixing energy requirements while producing reasonably high conversion yields.

Biotechnology↗
PubMed2001

Reduced inhibition of enzymatic hydrolysis of steam-pretreated softwood.

Softwood constitutes the main source of lignocellulosic material in Sweden which can be used for ethanol production from renewable resources. To make the biomass-to-ethanol process more economically feasible, it is preferable to include the sugar-rich prehydrolysate, i.e. the liquid obtained after the pretreatment step, in the enzymatic hydrolysis of the solid fraction. This study shows that the prehydrolysate inhibits cellulose conversion in the enzymatic hydrolysis step. When the prehydrolysate was included in the enzymatic hydrolysis, the cellulose conversion was reduced by up to 36%. However, this inhibition can be overcome by fermentation of the prehydrolysate prior to enzymatic hydrolysis.

Journal Article↗
PubMed2001

Separation of lactic acid-producing bacteria from fermentation broth using a ceramic microfiltration membrane with constant permeate flow.

The influence of several operating parameters on the critical flux in the separation of lactic acid-producing bacteria from fermentation broth was studied using a ceramic microfiltration membrane equipped with a permeate pump. The operating parameters studied were crossflow velocity over the membrane, bacterial cell concentration, protein concentration, and pH. The influence of the isoelectric point (IEP) of the membrane was also investigated. In the interval studied (5.3-10.8 m/s), the crossflow velocity had a marked effect on the critical flux. When the crossflow velocity was increased the critical flux also increased. The bacterial cells were retained by the membrane and the concentration of bacterial cells did not affect the critical flux in the interval studied (1.1-3.1 g/L). The critical flux decreased when the protein concentration was increased. It was found that the protein was adsorbed on the membrane surface and protein retention occurred even though the conditions were such that no filter cake was present on the membrane surface. When the pH of the medium was lowered from 6 to 5 (and then further to 4) the critical flux decreased from 76 L/m(2)h to zero at both pH 5 and pH 4. This was found to be due to the fact that the lowering in pH had affected the physiology of the bacterial cells so that the bacteria tended to adhere to the membrane and to each other. The critical flux, for wheat flour hydrolysate without particles, was much lower (28 L/m(2)h) when using a membrane with an IEP of 5.5 than the critical flux of a membrane with an IEP at pH 7 (96 L/m(2)h). This was found to be due to an increased affinity of the bacteria for the membrane with the lower IEP.

Bacterial Proteins↗
PubMed2001

Conversion of sodium lactate to lactic acid with water-splitting electrodialysis.

The conversion of sodium lactate to lactic acid with water-splitting electrodialysis was investigated. One way of reducing the power consumption is to add a conductive layer to the acid compartment. Doing this reduced the power consumption by almost 50% in a two-compartment cell, whereas the electric current efficiency was not affected at all. Three different solutions were treated in the electrodialysis unit: a model solution with 70 g/L of sodium lactate and a fermentation broth that had been prefiltered two different ways. The fermentation broth was either filtered in an open ultrafiltration membrane (cut-off of 100,000 Dalton) in order to remove the microorganisms or first filtered in the open ultrafiltration membrane and then in an ultrafiltration membrane with a cut-off of 2000 Dalton to remove most of the proteins. The concentration of sodium lactate in the fermentation broth was 70 g/L, as well. Organic molecules present in the broth (peptides and similar organic material) fouled the membranes and, therefore, increased power consumption. Power consumption increased more when permeate from the more open ultrafiltration membrane was treated in the electrodialysis unit than when permeate from the membrane with the lower cut-off was treated, since there was a higher amount of foulants in the former permeate. However, the electrodialysis membranes could be cleaned efficiently with a 0.1 M sodium hydroxide solution.

Cell Compartmentation↗
PubMed2000

Use of holographic laser interferometry to study the diffusion of polymers in gels.

The aim of this study was to demonstrate the potential for holographic interferometry to be used for diffusion studies of large molecules in gels. The diffusion and partitioning of BSA (67,000 g/mol) and pullulans (5,900-112,000 g/mol) in agarose gel were investigated. The gel diffusion coefficients obtained for BSA were higher when distilled water was used as a solvent compared to those obtained with 0.1 M NaCl as the solvent. Furthermore, the gel diffusion coefficient increased with increasing BSA concentration. The same trend was found for liquid BSA diffusion coefficients obtained by DLS. BSA partition coefficients obtained at different agarose gel concentrations (2-6%, w/w) decreased slightly with increasing gel concentration. However, all BSA gel diffusion coefficients measured were significantly lower than those in pure solvent and they decreased with increasing agarose concentration. The gel diffusion coefficients obtained for pullulans decreased with increasing pullulan molecular weight. The same effect from increased molecular weight was seen in the liquid diffusion coefficients measured by DLS. The pullulan partition coefficients obtained decreased with increasing molecular weight. However, pullulans with a larger Stokes' radius than BSA had partition coefficients that were higher or approximately the same as BSA. This implied that the pullulan molecules were more flexible than the BSA molecules. The results obtained for BSA in this study agreed well with other experimental studies. In addition, the magnitude of the relative standard deviation was acceptable and in the same range as for many other methods. The results thereby obtained showed that holographic interferometry is a suitable method for studying diffusion of macromolecules in gels.

Diffusion↗
PubMed2000

Diffusion of lysozyme in gels and liquids. A general approach for the determination of diffusion coefficients using holographic laser interferometry.

A study on diffusion measurements of the protein lysozyme in liquids and agarose gels, at different pH and ionic strengths, has been performed using holographic laser interferometry. The measurements showed that the diffusive flux was very dependent on pH and ionic strength when the protein was not at its isoelectric point or when the charge of the lysozyme molecules was not screened by ions in the solution. Evaluation of the experimental data with Fick's law, resulted in diffusion coefficients for lysozyme that are strongly dependent on pH and ionic strength. Evaluation of the experimental data using a more general transport model, based on chemical potential gradients instead of concentration gradients resulted in lysozyme diffusion coefficients that are independent of pH and ionic strength. The chemical potential was estimated by using the Poisson-Boltzmann equation.

Diffusion↗
PubMed2000

Effect of substrate and cellulase concentration on simultaneous saccharification and fermentation of steam-pretreated softwood for ethanol production.

Economic optimization of the production of ethanol by simultaneous saccharification and fermentation (SSF) requires knowledge about the influence of substrate and enzyme concentration on yield and productivity. Although SSF has been investigated extensively, the optimal conditions for SSF of softwoods have yet not been determined. In this study, SO2-impregnated and steam-pretreated spruce was used as substrate for the production of ethanol by SSF. Commercial enzymes were used in combination with the yeast Saccharomyces cerevisiae. The effects of the concentration of substrate (2% to 10% w/w) and of cellulases (5 to 32 FPU/g cellulose) were investigated. SSF was found to be sensitive to contamination because lactic acid was produced. The ethanol yield increased with increasing cellulase loading. The highest ethanol yield, 68% of the theoretical based on the glucose and mannose present in the original wood, was obtained at 5% substrate concentration. This yield corresponds to 82% of the theoretical based on the cellulose and soluble glucose and mannose present at the start of SSF. A higher substrate concentration caused inefficient fermentation, whereas a lower substrate concentration, 2%, resulted in increased formation of lactic acid, which lowered the yield. Compared with separate hydrolysis and fermentation, SSF gave a higher yield and doubled the productivity.

Carbohydrate Metabolism↗
PubMed2000

Cellulase production of Trichoderma reesei Rut C 30 using steam-pretreated spruce. Hydrolytic potential of cellulases on different substrates.

Various techniques are available for the conversion of lignocellulosics to fuel ethanol. During the last decade processes based on enzymatic hydrolysis of cellulose have been investigated more extensively, showing good yield on both hardwood and softwood. The cellulase production of a filamentous fungi, Trichoderma reesei Rut C 30, was examined on carbon sources obtained after steam pretreatment of spruce. These materials were washed fibrous steam-pretreated spruce (SPS), and hemicellulose hydrolysate. The hemicellulose hydrolysate contained, besides water-soluble carbohydrates, lignin and sugar degradation products, which were formed during the pretreatment and proved to be inhibitory to microorganisms. Experiments were performed in a 4-L laboratory fermentor. The hydrolytic capacity of the produced enzyme solutions was compared with two commercially available enzyme preparations, Celluclast and Iogen Cellulase, on SPS, washed SPS, and Solka Floc cellulose powder. There was no significant difference among the different enzymes produced by T. reesei Rut C 30. However, the conversion of cellulose using these enzymes was higher than that obtained with Iogen or Celluclast cellulases using steam-pretreated spruce as substrate.

Cellobiose↗
PubMed2000

Simultaneous saccharification and fermentation of steam-pretreated spruce to ethanol.

Ethanol production was studied in simultaneous saccharification and fermentation (SSF) of steam-pretreated spruce at 42 degrees C, using a thermotolerant yeast. Three yeast strains of Kluyveromyces marxianus were compared in test fermentations. SSF experiments were performed with the best of these on 5% (w/w) of substrate, at a cellulase loading of 37 filter paper units/g of cellulose, and a beta-glucosidase loading of 38 IU/g of cellulose. The detoxification of the substrate and the lack of pH control in the experiments increased the final ethanol concentration. The final ethanol yield was 15% lower compared to SSF with Saccharomyces cerevisiae at 37 degrees C, owing to the cessation of ethanol fermentation after the first 10 h.

Cellulase↗
PubMed2000

Effect of acetic acid and furfural on cellulase production of Trichoderma reesei RUT C30.

Because of the high temperature applied in the steam pretreatment of lignocellulosic materials, different types of inhibiting degradation products of saccharides and lignin, such as acetic acid and furfural, are formed. The main objective of the present study was to examine the effect of acetic acid and furfural on the cellulase production of a filamentous fungus Trichoderma reesei RUT C30, which is known to be one of the best cellulase-producing strains. Mandels's mineral medium, supplemented with steam-pretreated willow as the carbon source at a concentration corresponding to 10 g/L of carbohydrate, was used. Four different concentration levels of acetic acid (0-3.0 g/L) and furfural (0-1.2 g/L) were applied alone as well as in certain combinations. Two enzyme activities, cellulase and beta-glucosidase, were measured. The highest cellulase activity obtained after a 7-d incubation was 1.55 FPU/mL with 1.0 g/L of acetic acid and 0.8 g/L of furfural added to the medium. This was 17% higher than that obtained without acetic acid and furfural. Furthermore, the results showed that acetic acid alone did not influence the cellulase activity even at the highest concentration. However, beta-glucosidase activity was increased with increasing acetic acid concentration. Furfural proved to be an inhibiting agent causing a significant decrease in both cellulase and beta-glucosidase production.

Acetic Acid↗
PubMed1999

Separation of cells and proteins from fermentation broth in a shear-enhanced cross-flow ultrafiltration module as the first step in the refinement of lactic acid.

A shear-enhanced, cross-flow ultrafiltration module was used to separate cells and proteins from the fermentation broth. Three (fermented) media were studied: rich medium, rich medium with hydrolytic enzymes added after fermentation, and wheat flour hydrolysate. To find a membrane with as high a flux as possible, but still capable of separating cells and proteins from the lactic acid containing broth, the performance of three hydrophilic membranes of varying cutoffs (10,000, 20,000, and 30,000) and one hydrophobic membrane (cutoff 25,000) was investigated. The proteins produced by the lactic acid bacteria during fermentation and the hydrolytic proteins were retained by the hydrophilic membrane with a cutoff of 20,000, whereas wheat flour proteins were detected in the permeate. In the permeates from the hydrophobic membrane (cutoff 25,000), almost no proteins were detected. The flux of the whole-wheat flour hydrolysate was significantly lower than that of rich medium, for both the hydrophilic and the hydrophobic membranes. The flux was, in all cases, higher for the hydrophilic membrane (12-85 L/[m2 x h], depending on which medium was treated) than for the hydrophobic one (8-45 L/[m2 x h]), even though the nominal cutoffs of the hydrophobic and hydrophilic membranes were almost the same. However, the difference in flux was smaller when the whole-wheat flour hydrolysate was processed (12 vs 8 L/[m2 x h]) than when the rich medium was processed (85 vs 45 L/[m2 x h]). Protein retention was higher for the hydrophobic membrane than for the hydrophilic membrane (cutoff 20,000) owing to blocking of the pores by proteins adsorbed on to the hydrophobic membrane surface.

Journal Article↗
PubMed1998

Swelling kinetics of poly(N-isopropylacrylamide) gel.

In many gel applications the swelling and shrinking kinetics are very important, e.g. in controlled/slow release, where the kinetics determined the rate of out-diffusion of the active component, and in gel extraction where the gel is swollen and shrunk several times. In this study swelling kinetics of poly(N-isopropylacrylamide) gel (NiPAAm gel) was determined by monitoring the swelling process using a stereo microscope and a video camera. The swelling of spherical gel bodies could conveniently be studied after a temperature change. The results obtained were treated according to the approach of Tanaka and Fillmore, in which the swelling and shrinking of a gel is described as a motion of the gel network according to the diffusion equation. This was shown to be valid when the temperature changes are kept below the critical point of the gel. However, the model fails to describe the shrinking process when passing from below to above the critical temperature. The collective diffusion coefficient (D), defined as the osmotic bulk modulus divided by the friction factor, was determined by fitting to the experimental data. D was found to increase with temperature according to the Wilke-Chang relation D = 2.0.10(-11) + 7.6.10(-17).T/mu. The results were used to simulate the swelling/shrinking process. The simulations show the importance of having sufficiently small gel bodies to achieve a short swelling time.

Acrylic Resins↗
PubMed1998

Use of hemicellulose hydrolysate for beta-glucosidase fermentation.

Hydrolysis of cellulose by Trichoderma cellulases often results in a mixture of glucose, cellobiose, and low-mol-wt cellodextrins. Cellobiose is nonfermentable for most yeasts, and therefore it has to be hydrolyzed to glucose by beta-glucosidase prior to ethanol fermentation. In the present study, the beta-glucosidase production of one Penicillium and three Aspergillus strains, which were previously selected out of 24 strains, was investigated on steam pretreated willow. Both steam-pretreated willow and hemicellulose hydrolysate, released during steam explosion of willow, were used as carbon sources. Reference cultivation runs were performed using prehydrolyzed Solka Floc and glucose. The four strains were compared with Trichoderma reesei regarding sugar consumption and beta-glucosidase production. Aspergillus niger and Aspergillus phoenicis proved to be the best enzyme producers on hemicellulose hydrolysate. The maximum beta-glucosidase activity, 4.60 IU/mL, was obtained when A. phoenicis was cultivated on the mixture of hemicellulose hydrolysate and steam-pretreated willow. The maximum yield of enzyme activity, 502 IU/g total carbohydrate, was obtained when Aspergillus foetidus was cultivated on the hemicellulose hydrolysate.

Aspergillus↗
PubMed1997

Diffusion of glucose and insulin in a swelling N-isopropylacrylamide gel.

The diffusional characteristics for poly(N-isopropylacrylamide) (NiPAAm) gel have been investigated. This gel is a critical gel which means that small changes in the environment influence the gel volume considerably. The effective diffusion coefficients for the solutes glucose and insulin were determined in batch experiments with the solutes diffusing out from small cylindrical gel bodies with diameters of 2.4-2.9 mm and at temperatures below the critical temperature: 10, 20 and 30 degrees C. The effective diffusion coefficients were obtained by fitting the experimental data to a mathematical model considering back-mixing and time delay in the experimental set-up, dilution due to the adsorbed liquid on the gel bodies and partition due to the exclusion effect. The effective diffusion coefficient for glucose increases from 2.7.10(-10) to 4.7.10(-10) m(2)/s when the temperature increases from 10 to 30 degrees C, following the Wilke-Chang relationship. This implies that the effect of the network is negligible compared with the effect of the temperature. However, for a solute with a molecular weight of about 6000 the network has a considerable effect. The effective diffusion coefficient for insulin increases from 4.4.10(-10) to 5.9.10(-10) m(2)/s when the temperature increases from 10 to 30 degrees C, which is less than expected from the Wilke-Chang relationship. This indicates an increased resistance for diffusion inside the gel due to shrinking.

Journal Article↗
PubMed1996

Influence of experimental errors on the determination of flux control coefficients from transient metabolite concentrations.

The influence of experimental errors on the determination of flux control coefficients from transient metabolite concentrations with the method proposed by Delgado and Liao [(1992) Biochem. J. 282, 919-927] has been investigated by using Monte Carlo simulations. The method requires least-squares fitting of the transient metabolite concentrations. Three different fitting methods have been evaluated. Simulated metabolite concentrations of a fictive metabolic pathway were scattered randomly, emulating experimental errors, before performing the fits. This was repeated a large number of times; the mean values and standard deviations of the resulting control coefficients are reported. The results show that the proposed method for determining control coefficients is too sensitive to experimental errors to be practicable, with theoretically justified fitting methods. This is in particular due to the high degree of correlation between the concentrations. An alternative ad hoc fitting method produced biased mean values of the estimates of the control coefficients, but with remarkably low standard deviations.

Biometry↗