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Biochemical Engineering Journal (v.50, #1-2)
A stoichiometric analysis of biological xylitol production by Juan S. Aranda-Barradas; Claudio Garibay-Orijel; Jesús A. Badillo-Corona; Edgar Salgado-Manjarrez (pp. 1-9).
In the biological production of xylitol from xylose it has been demonstrated that a low-level supply of oxygen to the culture (∼0.1 volume of air per volume of culture medium per minute) yields an increase of extracellular accumulated xylitol up to 0.65gxylitolgxylose−1 in our experiments. In spite of the abundant experimental evidence regarding xylitol production, the advances in the mathematical description of the process are relatively scarce. In this work, a stoichiometric model considering the main biochemical reactions (metabolic fluxes) involved in microaerobic xylitol production is proposed. The main metabolic reactions in xylitol production by Candida parapsilosis were incorporated in order to establish a stoichiometric reaction rate analysis of the network. The reaction rates in the metabolic network were calculated both for determined and underdetermined systems. A comparison between predicted and experimentally measured or reported yields has shown that the proposed stoichiometric model correctly depicts the xylitol yield within a 12.8% average error for several xylose-assimilating yeasts. The expected xylitol concentrations for a production process were also estimated after a sensitivity analysis of the metabolic network. An analysis of the estimated metabolic fluxes provided insight into some physiological events involved in the production of xylitol by yeasts.
Keywords: Xylose; Xylitol; Candida parapsilosis; Metabolic network; Stoichiometric matrix; Stoichiometric model
Electricity generation from synthetic substrates and cheese whey using a two chamber microbial fuel cell by Georgia Antonopoulou; Katerina Stamatelatou; Symeon Bebelis; Gerasimos Lyberatos (pp. 10-15).
In this study, the possibility of electricity generation from diluted cheese whey in a two-chamber mediator-less microbial fuel cell (MFC) was investigated. Synthetic substrates such as glucose and lactose were also used for characterization of the MFC and for microbial acclimation at the anode compartment. The maximum power density obtained using diluted cheese whey was 18.4mW/m2 (normalized to the geometric area of the anodic electrode, which was 13.8cm2), corresponding to a current density of 80mA/m2 and a MFC voltage of 0.23V. The coulombic efficiency ɛcb was very low (only 1.9%), implying that a pretreatment step of raw cheese whey is essential prior to use. For comparison, in the case of sugars (glucose and lactose) the obtained maximum power density was 15.2mW/m2 with ɛcb equal to 28% for glucose and 17.2mW/m2 with ɛcb equal to 22% for lactose. Impedance spectroscopy measurements showed that the dominant contribution to the cell overpotential was due to the ohmic resistance of the MFC. The contribution of the electrode overpotentials was also significant, mainly that of the cathode overpotential.
Keywords: Microbial fuel cell; MFC; Glucose; Lactose; Cheese whey; Impedance spectroscopy
Improving Jatropha curcas seed protein recovery by using counter current multistage extraction by Dianika Lestari; Wim Mulder; Johan Sanders (pp. 16-23).
Jatropha curcas seed press cake contains 23wt% proteins (dry basis). Due to the toxic compounds in Jatropha, we will use the proteins for non-food applications. Related to non-food applications, an efficient protein extraction to obtain a high protein recovery and high protein concentration with good protein functional properties is required. To achieve this, we conducted protein extractions at room temperature by using different solvents at various solvent to solid ratios and performed multistage counter current extraction to improve protein recovery and protein concentration. We obtained the highest protein recovery of 82% by using 0.055M NaOH at solvent to solid ratio of 10g/g after four-stage counter current extraction. By using 0.055M NaOH extraction at lower solvent to solid ratio of 4g/g, protein recovery was 35% after one-stage extraction and improved up to 71% with a high protein concentration of 63mg/mL after four-stage counter current extraction. The highest amount of protein was precipitated from crude extracts at pH 4–5.5 and resulted on precipitate with protein content of 70%. The multistage counter current extraction did not influence Jatropha seed protein molecular weight distributions, which were within the range of 3–98kDa.
Keywords: Jatropha curcas; Counter current extraction; Protein recovery; Molecular weight distribution; Precipitation; Biorefinery
Kinetic analysis and pH-shift control strategy for poly(γ-glutamic acid) production with Bacillus subtilis CGMCC 0833 by Qun Wu; Hong Xu; Hanjie Ying; Pingkai Ouyang (pp. 24-28).
Production of poly(γ-glutamic acid) (γ-PGA) by Bacillus subtilis CGMCC 0833 was investigated. It was influenced by the utilization of extracellular substrate glutamate, which was a relatively low-efficiency procedure in γ-PGA fermentation. Then it was discovered that the glutamate utilization was greatly dependent on the medium pH. However, the optimal pH for glutamate utilization was not consistent with that for the cell growth. Therefore, in order to obtain the optimal production of γ-PGA, a two-stage pH-shift control strategy was proposed. At first 24h, pH was controlled at 7.0 to obtain the maximum biomass, and then shifted to 6.5 to obtain high level of glutamate utilization and γ-PGA production. By applying such a pH-shift control strategy, the glutamate utilization increased from 24.3 to 29.5g/l, the intracellular glutamate, which was the direct substrate, also increased, and consequently the yield of γ-PGA increased from 22.2 to 27.7g/l, increased by 24.8%. This was the first report of using a two-stage pH-shift control strategy in γ-PGA production, and it was proved to be an effective way for the optimization of γ-PGA production in this strain.
Keywords: Bacillus subtilis; CGMCC 0833; Fermentation; Glutamate transport; Kinetic analysis; pH-shift control; Poly(γ-glutamic acid)
Tailoring the enzymatic synthesis and nanofiltration fractionation of galacto-oligosaccharides by Vanessa A. Botelho-Cunha; Marília Mateus; José C.C. Petrus; Maria N. de Pinho (pp. 29-36).
Continuous galacto-oligosaccharides (GOS) synthesis by bead-immobilized β-galactosidase and nanofiltration fractionation of derived sugar mixtures by cellulose acetate membranes are investigated. Upon enzyme adsorption assays (8mL/g of solution/resin ratio, 150mg/mL of initial enzyme concentration and 14±1.4mgprotein/gresin), a Langmuir-type isotherm is observed. Enzyme concentration of 10U/mL, selected in batch reactor experiments, is used for continuous GOS production carried out at lactose concentrations of 150g/L and 300g/L, and at 40°C. Total dissolved solids concentration influences both reaction and saccharide mixtures fractionation. All observed sugar retention coefficients, mainly for monosaccharides, increase with transmembrane pressure and a gap between the retention values of synthesized disaccharides and lactose (87% versus 77%, respectively, for 2bar/40°C) is displayed as a function of the effective transmembrane pressure and total sugars concentration. At 150g/L total sugars in feed, trisaccharides are totally retained. Doubling sugars concentration, trisaccharides retentions decreased for all applied pressures, reaching 90%.
Keywords: Nanofiltration; Enzyme immobilization; Oligosaccharides synthesis; Saccharides fractionation
Heat transfer modeling of radio frequency assisted packed bed extraction of an anticancer agent (podophyllotoxin) by M. Izadifar; O.D. Baik (pp. 37-46).
Podophyllotoxin is considered as an outstanding anti-tumor agent against lung cancer which is commercially extracted by the percolation of warm ethanol through packed beds of dried rhizomes of Podophyllum emodi or Podophyllum peltatum. Radio frequency (RF) heating can be used for uniform heating of the packed bed during the extraction. Based on local volume averaging (LVA) and local thermal equilibrium (LTE), a mathematical model with variable properties was developed for transient heat transfer during RF-assisted packed bed extraction of podophyllotoxin. The validity of LVA and LTE was assessed by evaluating the length scale, time scale, and convective constraint. A control function was included in the model to take into account the effect of a temperature controller functioning during the actual RF-assisted packed bed extraction. For a vertical packed bed reactor subjected to RF heating, two governing equations associated with the packed bed and the solvent phase at the top of the bed were numerically solved using implicit-finite difference and Gauss–Seidel methods. The simulation results had a good agreement with the experimental data. Heat transfer simulation was performed for different flow rates of ethanol/water solution with different dielectric properties during the RF-assisted packed bed extraction process.
Keywords: Modeling; Packed bed extraction; Podophyllotoxin; Radio frequency heating
Construction and operation of a fibrous bed reactor with immobilized lactonase for efficient production of ( R)-α-hydroxy-γ-butyrolactone by Xian Zhang; Jian-He Xu; Dian-Hua Liu; Jiang Pan; Bing Chen (pp. 47-53).
Optically active ( R)-α-hydroxy-γ-butyrolactone ( R-HBL) was produced via enantioselective hydrolysis of racemic HBL using a lactonase extracted from Fusarium proliferatum ECU2002 (FPL). Different carriers were examined for immobilizing FPL and the highest activity was observed when the enzyme was adsorbed onto cotton cloth followed by cross-linking with glutaraldehyde. A fibrous bed reactor (FBR) was constructed by packing a piece of cotton cloth (∼2g) coiled together with a wire net into a glass column (Ø1.5cm×12cm) thermostated at 30°C. Kinetic resolution of RS-HBL was carried out semi-continuously in the FBR by recirculating a racemic lactone solution through the reactor at a certain flow rate. The performance and productivity of the FBR were evaluated by several critical parameters, including enzyme load, initial RS-HBL concentration and so on. Immobilized FPL (IFPL, ∼40U) per 50ml of working volume was found to be the optimal enzyme load, and the most suitable substrate concentration was 750mM at 30°C with an appropriate height to diameter ( H/ D) ratio (5.0). The IFPL-catalyzed kinetic resolution of RS-HBL was successfully operated in the FBR for 60 batches, with an average productivity of 2.48gl−1h−1 ( R-HBL) in high optical purity (90.0–96.4% ee) in the case of semi-continuous operation.
Keywords: Enzyme; Bioreactor; Kinetics; Immobilized; (; RS; )-α-Hydroxy-γ-butyrolactone; Fusarium proliferatum; lactonase
Batch kinetics of ferrous iron oxidation by Leptospirillum ferriphilum at moderate to high total iron concentration by Kalin Penev; Dimitre Karamanev (pp. 54-62).
A study of the kinetics of ferrous iron oxidation by a free suspended culture of the bacterium Leptospirillum ferriphilum in batch regime at moderate to high iron concentrations was conducted. A circulating bed airlift bioreactor was used in order to obtain reliable biokinetic data, unaffected by biofilm growth. The two major factors in consideration were the effects of the pH and the total iron concentration in the range of 5–40g/L. The optimal pH was found between 1.05 and 1.80. In this range a strictly growth associated biooxidation with constant yield coefficient was proven, while at suboptimal pH values non-growth associated iron biooxidation was shown at pH as low as 0.4. This effect was taken into consideration for the derivation of a Monod-type kinetic model, derived on first principles from the electrochemical-enzymatic model for ferrous iron biooxidation. Our model shows a linear dependence between the apparent half-saturation constant ( Kapp) and the total iron concentration in studied range of iron concentration.
Keywords: Leptospirillum ferriphilum; Extremophiles; Iron biooxidation; Kinetic modeling; Airlift bioreactor
Design and performance evaluation of a microwave based low carbon yielding extraction technique for naturally occurring bioactive triterpenoid: Oleanolic acid by Vivekananda Mandal; Subhash C. Mandal (pp. 63-70).
An ecofriendly microwave-assisted extraction (MAE) technique with a low carbon output was developed for the rapid extraction of bioactive oleanolic acid from Gymnema sylvestre. Several different influential extraction parameters such as microwave power, extraction time, solvent type, solvent composition, preleaching time, loading ratio and extraction cycle were studied in a systematic fashion for the determination of optimum extraction conditions. Under optimum conditions, 8min of MAE produced a maximum yield of 7.6% (w/w) of oleanolic acid which was found to be 4 times, 3 times and 1.2 times more efficient than maceration, stirring extraction and heat reflux extraction, respectively. Extracts obtained from 8min of MAE showed better antioxidant activity when compared to other conventional methods. No degradation of the target analyte was observed at the optimum conditions as evidenced from the stability studies performed with standard oleanolic acid. The proposed method also showed high degree of reproducibility. From the results of scanning electron microscopy a new synergistic phenomenon of heat transfer and mass transfer was proposed.
Keywords: Gymnema sylvestre; Oleanolic acid; Microwave-assisted extraction; Synergistic; Antioxidant; Extraction time
Immobilization of activated sludge in poly(ethylene glycol) by UV technology and its application in micro-polluted wastewater by Qiao Xiangli; Liu Zhe; Liu Zhiwei; Zeng Yinglin; Zhang Zhengjia (pp. 71-76).
A new method, ultraviolet (UV) technology, was utilized to immobilize activated sludge in poly(ethylene glycol) (PEG) gel carriers. A number of characteristics of immobilized cells, such as water content, oxygen uptake rate, and protein content, were examined, and performance in batch culture for treating synthetic micro-polluted wastewater with different C/N ratios and different pH values was also investigated. The bioactivity of immobilized cells was maintained during immobilization and the cells showed high nitrification activity after 10–15d acclimation. Ammonia removal increased with C/N ratio while TOC removal decreased with it. However, more than 85% of the ammonia nitrogen and 72% of the TOC could be reduced in 4–6h in all cases. No obvious effects on nitrification were seen for pH shocks at pH 6, 7, 8 or 9, but a pH shock at pH 5 caused a 30% loss of nitrification efficiency. SEM images showed that the immobilization beads were highly porous and that immobilized nitrifiers dominated the surface and within the core of the gel beads.
Keywords: Immobilized cell; Activate sludge; Waste treatment; Aerobic digestion; Microbial; Biopolymers
Multi-objective process optimization and integration for the sequential and increased production of biomass, lipase and endospores of a probiotic bacterium by Subhasish Das; Shailesh Kharkwal; Saurabh K. Pandey; Ramkrishna Sen (pp. 77-81).
The objective of this study was to substantially enhance the yields of lipase, biomass and spores from a sporogenous probiotic bacterium, Bacillus coagulans RK-02 by multivariate response surface modeling and genetic algorithm based optimization. The effect of temperature, agitation and aeration on time course of growth, lipase formation and sporulation of individual batch cultivation were also studied. The optimum conditions for three responses were found to be different from each other. Comparatively lower temperature and higher agitation and aeration were needed for biomass and lipase production than that for maximizing sporulation rate. In the final validation experiment, three different optimal conditions for maximizing each of these responses, namely biomass, lipase and spore yields, in a stage wise manner were maintained respectively. This strategy produced 6.25gL−1 biomass, 6×1012 spores per gram of biomass, and maximum of 13.46IU lipase. Such high yield of biomass, lipase and spore from batch cultivation is first ever to be reported.
Keywords: Bacillus coagulans; RK-02; Probiotic; Biomass; Spore; Lipase; Multivariate optimization