| 1. |
- Björnsson, Lovisa, et al.
(författare)
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Utilisation of a Pd-MOS sensor for on-line monitoring of dissolved hydrogen in anaerobic digestion
- 2001
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 73:1, s. 35-43
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Tidskriftsartikel (refereegranskat)abstract
- The use of a hydrogen-sensitive palladium-metal oxide semiconductor (Pd-MOS) sensor in combination with a membrane for liquid-to-gas transfer for the detection of dissolved hydrogen was investigated. The system was evaluated with known concentrations of dissolved hydrogen in water. The lowest concentration detected with this set-up was 160 nM. The method was applied to monitoring of a laboratory-scale anaerobic digestion process employing mixed sludge containing mainly food/industrial waste. Pulse loads of glucose were added to the system at different levels of microbial activity, and the microbial status of the culture was reflected in the dissolved hydrogen response. Simultaneous headspace hydrogen measurements were performed, and at the lower levels of dissolved hydrogen no corresponding headspace hydrogen could be detected. When glucose was added to a resting culture the dissolved hydrogen response was rapid and the first response could be detected 9 min after addition of glucose, whereas headspace hydrogen concentrations increased only after 80 to 110 min. This indicates limitations in the liquid-to-gas hydrogen transfer and illustrates the importance of hydrogen monitoring in the liquid. The sensor system developed is flexible, the membrane is easily replaceable, and the probe for liquid-to-gas hydrogen transfer can be adjusted easily to large-scale applications.
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| 2. |
- Persson, A, et al.
(författare)
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Separation of lactic acid-producing bacteria from fermentation broth using a ceramic microfiltration membrane with constant permeate flow
- 2001
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 72:3, s. 269-277
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Tidskriftsartikel (refereegranskat)abstract
- 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 land 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. (C) 2001 John Wiley & Sons, Inc.
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| 3. |
- Roger, P, et al.
(författare)
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Use of holographic laser interferometry to study the diffusion of polymers in gels
- 2000
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 69:6, s. 654-663
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Tidskriftsartikel (refereegranskat)abstract
- 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. (C) 2000 John Wiley & Sons, Inc.
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| 4. |
- Frenander, U, et al.
(författare)
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Cell harvesting by cross-flow microfiltration using a shear-enhanced module
- 1996
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 52:3, s. 397-403
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Tidskriftsartikel (refereegranskat)abstract
- Protein, produced by a bacterial culture of recombinant Vibrio cholerae, was separated from cells in a fermentation broth by cross-flow microfiltration. A new, mechanically agitated (rotational) shear filter, the DMF(TM) filter from Pall, was used to perform the separation. Higher protein recovery and permeate flux than commonly obtained during cell harvesting were demonstrated using sixfold concentration followed by twofold diafiltration. The transmembrane pressure only increased by 10 kPa when the flux was kept constant at 150 L/m(2) h during both concentration and diafiltration. The protein transmission was about 100% initially, and over 90% at the end of the concentration process. The protein transmission during the diafiltration was over 80%. The total recovery of protein was 97%. When using an enzymatic cleaning agent, no significant pure water flux decrease was detected during the course of the experiments. (C) 1996 John Wiley & Sons, Inc.
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| 5. |
- Medve, József, et al.
(författare)
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Hydrolysis of microcrystalline cellulose by cellobiohydrolase I and endoglucanase II from Trichoderma reesei: Adsorption, sugar production pattern, and synergism of the enzymes
- 1998
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 59:5, s. 621-634
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Tidskriftsartikel (refereegranskat)abstract
- Microcrystalline cellulose (10 g/L Avicel) was hydrolysed by two major cellulases, cellobiohydrolase I (CBH I) and endoglucanase II (EG II), of Trichoderma reesei. Two types of experiments were performed, and in both cases the enzymes were added alone and together, in equimolar mixtures. In time course studies the reaction time was varied between 3 min and 48 h at constant temperature (40degreesC) and enzyme loading (0.16 µmol/g Avicel). In isotherm studies the enzyme loading was varied in the range of 0.08-2.56 µmol/g at 4degreesC and 90 min. Adsorption of the enzymes and production of soluble sugars were followed by FPLC and HPLC, respectively. Adsorption started quickly (50% of maximum achieved after 3 min) but was not completed before 60-90 min. For CBH I a linear relationship was observed between the production of soluble sugars and adsorption, showing that the average activity of the bound CBH I molecules does not change with increasing saturation. For EG II the corresponding curve levelled off which is explained by initial hydrolysis of loose ends on Avicel. The enzymes competed for binding sites, binding of EG II was considerably affected by CBH I, especially at high concentration. CBH I produced more soluble sugars than EG II, except at conversions below 1%. At 40degreesC when the enzymes were added together they produced 27-45% more soluble sugars than the sum of what they produced alone, i.e. synergistic action was observed (the final conversion after 48 h of hydrolysis was 3, 6, and 13% for EG II, CBH I, and their mixture, respectively). At 4degreesC, on the other hand, when the conversion was below 2.5%, almost no synergism could be observed. Molar proportions of the produced sugars were rather stable for CBH I (11-15%, 82-89%, and <6% for glucose, cellobiose, and cellotriose, respectively), while it varied considerably with both time and enzyme concentration for EG II. The observed stable but high glucose to cellobiose ratio for CBH I indicates that the processivity for this enzyme is not perfect. EG II produced significant amounts of glucose, cellobiose, and cellotriose, which are not the expected products of a typical endoglucanase activity on a solid substrate. We explain this by hypothesizing that EG II may show processivity due to its extended substrate binding site and the presence of its cellulose binding domain. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:621-634, 1998.
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| 6. |
- Planas, Jordi, et al.
(författare)
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Analysis of phase composition in aqueous two-phase systems using a two-column chromatographic method: Application to lactic acid production by extractive fermentation
- 1997
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 54:4, s. 303-311
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Tidskriftsartikel (refereegranskat)abstract
- A new chromatographic system for the simultaneous analysis of polyethylene glycol, dextran, sugars, and low-molecular-weight fatty acids was developed. The system is based on a gel exclusion column which allows a first separation between high- and low-molecular-weight compounds, and a cationic exchange column used to further separate the low-molecular-weight compounds. Two applications of the system were demonstrated: (i) after optimizing eluent conditions the gel exclusion column was used to determine the influence of lactic acid, phosphate buffer, and lactic acid bacteria on the ethylene oxide propylene oxide-dextran T40 phase diagram by HPLC; (ii) the ion exchange column was coupled in series with the gel exclusion column and the concentration of polyethylene glycol, dextran, glucose, lactate, acetate, and formate was determined in samples from the fermentative production of lactic acid in a polyethylene glycol 8000-dextran T40 aqueous two-phase system. The fermentation was operated without pH control in a repeated extractive batch mode, where the cell-free top phase was replaced four times, whereas the cell-containing bottom phase was reused repeatedly. The yield was 1.1 mol of lactic acid formed per mole of glucose added and the productivity was 4.7 mM.h-1. The polymeric composition of the fermentation system was monitored during the five repeated extractive batches, and it showed a progressive depletion in polyethylene glycol and a progressive enrichment in dextran. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 54: 303-311, 1997.
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| 7. |
- Planas, Jordi, et al.
(författare)
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Novel polymer-polymer conjugates for recovery of lactic acid by aqueous two-phase extraction
- 1999
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 66:4, s. 211-218
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Tidskriftsartikel (refereegranskat)abstract
- A new family of polymer conjugates is proposed to overcome constraints in the applicability of aqueous two-phase systems for the recovery of lactic acid. Polyethylene glycol-polyethylenimine (PEI) conjugates and ethylene oxide propylene oxide-PEI (EOPO-PEI) conjugates were synthesized. Aqueous two-phase systems were generated when the conjugates were mixed with fractionated dextran or crude hydrolyzed starch. With 2% phosphate buffer in the systems, phase diagrams with critical points of 3.9% EOPO-PEI-3.8% dextran (DEX) and 3.5% EOPO-PEI-7.9% crude starch were obtained. The phase separation temperature of 10% EOPO-PEI solutions titrated with lactic acid to pH 6 was 35degreesC at 5% phosphate, and increased linearly to 63degreesC at 2% phosphate. Lactic acid partitioned to the top conjugate-rich phase of the new aqueous two-phase systems. In particular, the lactic acid partition coefficient was 2.1 in 10% EOPO-PEI-8% DEX systems containing 2% phosphate. In the same systems, the partitioning of the lactic acid bacterium, Lactococcus lactis subsp. lactis, was 0.45. The partitioning of propionic, succinic, and citric acids was also determined in the new aqueous two-phase systems. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 66: 211-218, 1999.
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| 8. |
- Senthuran, A, et al.
(författare)
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Lactic acid fermentation in a recycle batch reactor using immobilized Lactobacillus casei.
- 1997
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 55:6, s. 841-853
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Tidskriftsartikel (refereegranskat)abstract
- Lactic acid production by recycle batch fermentation using immobilized cells of Lactobacillus casei subsp. rhamnosus was studied. The culture medium was composed of whey treated with an endoprotease, and supplemented with 2.5 g/L of yeast extract and 0.18 mM Mn(2+) ions. The fermentation set-up comprised of a column packed with polyethyleneimine-coated foam glass particles, Pora-bact A, and connected with recirculation to a stirred tank reactor vessel for pH control. The immobilization of L. casei was performed simply by circulating the culture medium inoculated with the organism over the beads. At this stage, a long lag period preceded the cell growth and lactic acid production. Subsequently, for recycle batch fermentations using the immobilized cells, the reducing sugar concentration of the medium was increased to 100 g/L by addition of glucose. The lactic acid production started immediately after onset of fermentation and the average reactor productivity during repeated cycles was about 4.3 to 4.6 g/L . h, with complete substrate utilization and more than 90% product yield. Sugar consumption and lactate yield were maintained at the same level with increase in medium volume up to at least 10 times that of the immobilized biocatalyst. The liberation of significant amounts of cells into the medium limited the number of fermentation cycles possible in a recycle batch mode. Use of lower yeast extract concentration reduced the amount of suspended biomass without significant change in productivity, thereby also increasing the number of fermentation cycles, and even maintained the D-lactate amount at low levels. The product was recovered from the clarified and decolorized broth by ion-exchange adsorption. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55:841-853, 1997.
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| 9. |
- Stenberg, K, et al.
(författare)
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Effect of substrate and cellulase concentration on simultaneous saccharification and fermentation of steam-pretreated softwood for ethanol production
- 2000
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 68:2, s. 204-210
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Tidskriftsartikel (refereegranskat)abstract
- 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. (C) 2000 John Wiley & Sons, Inc.
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| 10. |
- Torto, N, et al.
(författare)
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Monitoring of enzymatic hydrolysis of starch by microdialysis sampling coupled on-line to anion exchange chromatography and integrated pulsed electrochemical detection using post-column switching
- 1997
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 56:5, s. 546-554
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Tidskriftsartikel (refereegranskat)abstract
- A quantitative evaluation of the hydrolysis of wheat starch using Termamyl, a thermostable alpha-amylase (endo-l,4-alpha-D-glucan, glucanohydrolase; EC 3.2.1.78), is reported. Data from the monitoring of the hydrolysis of wheat starch indicated that, after 1 h, glucose and maltooligosaccharides up to DP 7 were the main hydrolysis products and thus enabled optimization of a liquefication step during the production of L-lactic acid. The monitoring system used, both in the on- and off-line mode, was based on continuous flow microdialysis sampling (CFMS) coupled to anion exchange chromatography and integrated pulsed electrochemical detection (IPED). A microdialysis probe equipped with a 5-mm polysulfone (SPS 4005) membrane, with a molecular-weight cut-off of 5 kDa, was used to sample the hydrolysis products of native wheat starch at 90 degrees C. Characteristic fingerprint separations were achieved by anion exchange chromatography after enzymatic hydrolysis. Post-column switching improved the detection and, consequently, also quantification of the hydrolysates as fouling of the electrode could be reduced. Maltooligosaccharide standards were used for quantification and to verify the elution of the hydrolysates by spiking the off-line samples. (C) 1997 John Wiley & Sons, Inc.
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