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Biochemical Engineering Journal (v.23, #1)
Evaluation of porous glass and zeolite as cells carriers for xylitol production from sugarcane bagasse hydrolysate by Júlio C. Santos; Solange I. Mussatto; Giuliano Dragone; Atílio Converti; Sílvio S. Silva (pp. 1-9).
Adsorbing carriers for immobilisation of Candida guilliermondii cells to use for xylitol production from sugarcane bagasse hemicellulose hydrolysate were tested. Biomass was immobilised in situ by natural adsorption, i.e. through direct contact between cells for the inoculum and carrier particles at the beginning of fermentations. The carriers employed were: Syrane porous glass beads with 2.53mm diameter in average and pore diameter in the range 60–300μm, supplied by Bioengineering (Wald, Switzerland), and NaX zeolite UOP WE 894 purchased from Plury QuÃmica S.A. (Diadema, SP, Brazil). At the end of the run with free cells taken as a reference test, xylitol concentration ( Pf) achieved 35.5g/l, corresponding to a xylose-to-xylitol yield factor ( YP/S) of 0.72g/g and a volumetric productivity ( QP) of 0.49g/lh, while final cell concentration ( Xf) and productivity ( Qx) were only 5.32g/l and 0.048g/lh, respectively. Both systems with immobilised cells exhibited lower xylitol productions ( Pf=28.8–29.5g/l, YP/S=0.52–0.53g/g, QP=0.32–0.33g/lh) and higher cell growth, with particular concern to porous glass ( Xf=10.5g/l, Qx=0.10g/lh). Electronic microscopy observations demonstrated that the excellent performance of porous glass as cell support was due to the development of a thick extracellular matrix either within the large pores or on the surface of this material. As a consequence, almost 50% of the cells resulted to be adsorbed to the carrier at the end of the run. This growth was also responsible for a decrease in the fraction of xylose available for xylitol production. Employing zeolite, a material with pore size smaller than cell size, immobilised cells represented only 30% of the final population and immobilisation was just observed on the carrier surface. The low cell attachment on this material can be explained by the stress exerted on the outer immobilised cells by the friction among beads.
Keywords: Porous glass; Zeolites; Immobilised cells; Hemicellulose hydrolysate; Fermentation; Xylitol
Enantioselective synthesis of ( S)-α-cyano-3-phenoxybenzyl alcohol by lipase-catalyzed alcoholysis of racemic ester in organic medium by Rong Zhou; Jian-He Xu (pp. 11-15).
Enantioselective synthesis of ( S)-α-cyano-3-phenoxybenzyl alcohol [( S)-CPBA] was successfully achieved by lipase-catalyzed alcoholysis of ( R, S)-CPBA acetate [( R, S)-CPBAc] in organic medium after systematic optimization of catalysts, water activity, organic solvents and acyl acceptors. A commercially available Pseudomonas fluorescens lipase, Lipase AK (Amano), showed excellent enantioselectivity (eep>99%, E=568) and high alcoholysis activity (1.88μmolmin−1mgenzyme−1) towards the ( S)-ester. The lipase exhibited higher activities in organic solvents with higher hydrophobicity and lower water activity controlled by anhydrous sodium sulfate. The initial rate of alcoholysis was nearly the same for alcohols of short chains (C2–C5) and the optimal concentration for n-butanol was 200–500mM. A celite-adsorbed preparation of Lipase AK was used repeatedly for eight times, without significant loss of enzyme activity.
Keywords: Pseudomonas fluorescens; lipase; Organic solvent; (; S; )-α-Cyano-3-phenoxybenzyl alcohol; Enantioselective alcoholysis; Repeated batch reactions
Novel immobilized metal ion affinity adsorbent based on cross-linked β-cyclodextrin matrix for repeated adsorption of α-amylase by Yu-Chieh Liao; Mei-Jywan Syu (pp. 17-24).
β-Cyclodextrin (β-CD) was chosen as the matrix material for the affinity binding of α-amylase in this work. β-CD was cross-linked with epichlorohydrin to improve its rigidity. Iminodiacetic acid (IDA), as a ligand, was bond with the cross-linked β-CD to increase the binding affinity for α-amylase. The affinity adsorbent thus prepared was further chelated with Cu2+ for the purpose of binding affinity and stability. The prepared affinity adsorbent was notated as β-CDcl–IDA-Cu2+. Excellent binding as well as de-binding was achieved within an extremely short period of time. Consequently, β-CDcl–IDA–Cu2+ successfully performed its ability on the affinity adsorption towards α-amylase. The adsorbent was also tested by its ability on repeated utilization. The result further confirmed that it could be repeatedly used and maintained the adsorption/desorption performance stably through many batches of operation. In addition, the bound α-amylase after many adsorption batches could be desorbed with a very high efficiency and hence rather high α-amylase activity could be collected.
Keywords: α-Amylase; β-Cyclodextrin; Cross-linked; Affinity adsorbent; Epichlorohydrin; Iminodiacetic acid; Chelating; Ligand; β-CD; cl; –IDA–Cu; 2+
Gas–liquid mass transfer studies with triple impeller system on a laboratory scale bioreactor by Meenal S. Puthli; Virendra K. Rathod; Aniruddha B. Pandit (pp. 25-30).
The gas–liquid mass transfer coefficient KL a in a fermentor is known to be a strong function of the mode of energy dissipation and physicochemical properties of the liquid media. Three impeller combinations namely, single, double and triple impellers, respectively have been tested in the laboratory bioreactor (2l) for their gas–liquid mass transfer performance. The liquid phase physico-chemical properties have been varied using distilled water, aqueous solutions of sodium carboxymethyl cellulose and simulated fermentation medium. The effects of the process variables such as the impeller speed, gas flow rate and the liquid phase physico-chemical properties on the volumetric liquid phase mass transfer coefficient of oxygen, KL a in a stirred bioreactor were investigated by static gassing out method. Correlations have been developed for the predictions of the gas–liquid mass transfer coefficient with liquids having different physico-chemical properties. It has been observed that triple impeller system gave highest values of gas–liquid mass transfer coefficient with the least power consumption.
Keywords: Gas–liquid mass transfer; Bioreactor; Triple impeller; Correlation studies; Dissolved oxygen; Power consumption
Kinetic studies on clavulanic acid degradation by Patrícia A. Bersanetti; Renata M.R.G. Almeida; Marlei Barboza; Maria Lucia G.C. Araújo; Carlos O. Hokka (pp. 31-36).
Clavulanic acid (CA), a potent beta-lactamase inhibitor, is very sensitive to pH and temperature. It is produced by Streptomyces clavuligerus and to optimize both the fermentation step and the downstream process, the expression of the hydrolysis kinetics has to be determined. In the present work the CA degradation rate from various sources was investigated at temperatures of 10, 20, 25, 30 and 40°C and pH values of 6.2 and 7.0. The results showed that first-order kinetics explained very well the hydrolysis kinetics and the Arrhenius equation could be applied to establish a relationship between the degradation rate constant and temperature, at both pHs. It has been observed that CA from fermentation medium was much more unstable than that from standard solution and from a commercially available medicine. Also, it was observed that CA was more stable at pH 6.2 than at pH 7.0, irrespective of the CA source.
Keywords: Abbreviation; CA; clavulanic acidAntibiotic; Clavulanic acid; Fermentation; Downstream processing; Degradation; Kinetic parameters
Indicator free DNA hybridization detection via EIS based on self-assembled gold nanoparticles and bilayer two-dimensional 3-mercaptopropyltrimethoxysilane onto a gold substrate by Yingzi Fu; Ruo Yuan; Lan Xu; Yaqin Chai; Xia Zhong; Dianping Tang (pp. 37-44).
A novel indicator free DNA biosensors fabricated by self-assembling of bilayer two-dimensional 3-mercaptopropyltrimethoxysilane (B2dMPTS), gold nanoparticles and oligonucleotide has been studied on gold substrate. The thiol groups of 3-mercaptopropyltrimethoxysilane (MPTS) serve as binding sites for the covalent attachment of MPTS to gold electrode surface. After hydrolysation and condensation, the polymerized monolayer, one-dimensional network of MPTS (1dMPTS) was combined together into a two-dimensional sol–gel network (2dMPTS). The second silane layer (B2dMPTS) was formed by immersing electrodes back into the MPTS solution overnight, and then the gold nanoparticles were chemisorbed onto the thiol groups of the second silane layer. Finally, the mercapto oligonucleotide was self-assembled onto the surface via the gold nanoparticles. Electrochemical impedance spectroscopy (EIS) was used to characterize the modified process. And we used the impedance spectroscopy as a platform for reagentless DNA sensing assay. The performance and factors influencing the performance of the resulting biosensor were studied in detail. The linear range of the biosensor was from 1.0×10−8 to 1.0×10−6M with a detection limit of 5.0×10−9M at 3 σ. In addition, the experiment results indicate that oligonucleotide immobilized on this way exhibits a good sensitivity, selectivity, stability and a long-term maintenance of bioactivity.
Keywords: Bilayer two-dimensional 3-mercaptopropyltrimethoxysilane; DNA immobilization; Gold nanoparticles; Electrochemical impedance spectroscopy
Facilitatory effect of immobilized lipase-producing Rhizopus oryzae cells on acyl migration in biodiesel-fuel production by Mitsuhiro Oda; Masaru Kaieda; Shinji Hama; Hideki Yamaji; Akihiko Kondo; Eiji Izumoto; Hideki Fukuda (pp. 45-51).
For biodiesel-fuel production by methanolysis of plant oils, Rhizopus oryzae cells producing a 1,3-positional specificity lipase were cultured with polyurethane foam biomass support particles (BSPs) in a 20l air-lift bioreactor, and the cells immobilized within BSPs were used as whole-cell biocatalyst in repeated batch-cycle methanolysis reaction of soybean oil. The whole-cell biocatalyst had a higher durability in the methanolysis reaction when obtained from air-lift bioreactor cultivation than from shake-flask cultivation. Following repeated methanolysis reaction using the whole-cell biocatalyst, analysis of the reaction mixture composition indicated that monoglycerides (MGs) decreased and free fatty acids (FFAs) increased with increasing water content in the reaction mixture, and that MGs, diglycerides (DGs), and triglycerides (TGs) increased with increasing number of reaction cycles. The isomers of MGs and DGs generated during the 20th methanolysis reaction cycle consisted of 2-MGs and 1,2(2,3)-DGs, respectively. The hydrolytic activity of the whole-cell biocatalyst, on the other hand, was stable regardless of the number of reaction cycles. It was demonstrated thus that the whole cell biocatalyst promotes acyl migration of partial glycerides, and that the facilitatory effect is increased by increase in the water content of the reaction mixture but it is lost gradually with increasing number of reaction cycles.
Keywords: Biodiesel fuel; Methanolysis; Rhizopus oryzae; Lipase; Whole-cell biocatalyst; Air-lift bioreactor; Acyl migration
Ginsenoside production by hairy root cultures of Panax ginseng: influence of temperature and light quality by Kee-Won Yu; Hosakatte Niranjana Murthy; Eun-Joo Hahn; Kee-Yoeup Paek (pp. 53-56).
Large-scale production of valuable secondary metabolites by plant cell cultures is generally hampered by low productivity. This productivity is affected by several physical factors like temperature and light. In this study we have investigated the impact of temperature and light quality on biomass accumulation and ginsenoside production by hairy roots cultivated in large-scale bioreactors. Biomass accumulation and ginsenoside production was optimal under 20°C/13°C day (12h)/night (8h) cycle. Biomass of hairy roots was highest in the cultures grown under dark or red light while ginsenoside accumulation was optimum in the cultures grown under fluorescent light.
Keywords: Bioreactors; Ginseng; Ginsenosides; Large-scale cultivation; Light quality; Plant cell culture; Metabolite production.
Simulation of competition between two microorganisms in a biofilm reactor based on different growth models by Mohammad R. Khoyi; Soheila Yaghmaei (pp. 63-72).
A simple biofilm model based on a model suggested by Soda et al. [S. Soda, E. Heinzle, M. Fujita, Modeling and simulation of competition between two microorganisms for a single inhibitory substrate in a biofilm reactor, Biotechnol. Bioeng. 66 (1999) 258–264] was used to simulate the competition between two microorganisms for space and a single inhibitory substrate in a biofilm reactor. Different growth kinetics were used to describe the growth of two microorganisms A and B which utilize the inhibitory substrate and the effect of biofilm thickness on microorganism concentration in biofilm was discussed. It was assumed that the biofilm has a uniform thickness and is composed of N segments ( N=4–10). The qualitative behavior of the biofilm reactor is characterized by four regions, I–IV, depending on the substrate concentration in feed, dilution rate, and growth kinetics. In region I, both microorganisms are washed out of the biofilm reactor. In region II, microorganism B is washed out of the biofilm and in region III microorganism A is washed out. In region IV both microorganism coexist with one another.
Keywords: Biofilm; Diffusion; Competition; Growth kinetics; Modeling; Substrate inhibition
Determination of kinetic parameters in fixed-film bio-reactors: an inverse problem approach by D. Kiranmai; A. Jyothirmai; C.V.S. Murty (pp. 73-83).
Processes employing bio-films are increasingly used nowadays for wastewater purification, because they are perceived to be highly efficient compared to the physical or chemical methods of treatment. Mathematical modelling of some of the bio-film processes is not always straightforward, however. A case in point is the fixed-film bioreactors, which have a microbial film attached to a solid inert packing material. The problem is mainly due to the difficulty in obtaining proper kinetic information about the biological reactions taking place in the bio-films. Some attempts have been reportedly made to determine these experimentally but the outcome is not wholly satisfactory. An alternative methodology is proposed in the present work, which makes use of a novel optimization method to evaluate the bio-kinetic parameters, in the course of the solution of an inverse problem with the aid of measured data of fractional conversion of the substrate. In this context, the importance of using a rigorous mathematical model to obtain an accurate estimate of the kinetics is emphasized. Also highlighted is the need to account for the variation of the bio-film thickness in the reactor and its dependence on the organic and the hydraulic loading rates.
Keywords: Anaerobic processes; Bio-films; Differential evolution; Fixed-bed bioreactors; Genetic algorithms; Inverse problem; Optimization and orthogonal collocation
Removal of ternary VOCs in air streams at high loads using a compost-based biofilter by Yonghui Liu; Xie Quan; Yazhi Zhao; Shuo Chen; Huimin Zhao (pp. 85-95).
Waste gases in the industry process are often characterized by the presence of multi-pollutants and concentration varieties of the compounds. In this study, the behavior of a biofilter system under high loads of ternary VOCs was studied. The biofilter was operated using a mixture of compost, lava and soil and applied to treat the air containing ethyl acetate, isopropanol and toluene. The biofilter treated up to 200gm−3bedh−1 of ethyl acetate and 120gm−3bedh−1 of isopropanol with percentage removals of nearly 100% and the empty bed retention time between 45 and 90s. Toluene removal efficiencies were in the range of 40–100% with the inlet concentration about 0.5gm−3 due to the inhibition of ethyl acetate and isopropanol. During the 3 months operation, filter media clogging/channeling, pH decrease and nitrogen loss from the media resulted in the deterioration of the biofilter performance. The results demonstrated that under the conditions of pH ranging from 6.4 to 7.4 and the nitrogen content of the media above 0.3mgg−1, the mixture of ethyl acetate, isopropanol and toluene could be treated effectively using a compost-based biofilter.
Keywords: Biofilters; VOCs; Biodegradation; Ethyl acetate; Isopropanol; Toluene