Biochemical Engineering Journal (v.4, #3)

Immobilization of rice (Oryza sativa L.) callus in polyurethane foam using a turbine blade reactor by Chunzhao Liu; Kwanhoon Moon; Hiroyuki Honda; Takeshi Kobayashi (169-175).
A turbine blade reactor (TBR) was employed to cultivate rice calli immobilized in polyurethane foam as a support. In the bioreactor, rice callus could be immobilized quickly in a 3 mm cube of the support, and then attached to the stainless mesh cylinder set at the center of the bioreactor. For improving the immobilization ratio of rice callus in the bioreactor, the optimum support volume and bioreactor operation and modification were investigated. The support volume had a pronounced effect on the immobilization ratio of rice callus, and the maximum volume was found to be 60 ml. By repeating a periodic operation three times (agitating at 300 rpm for 5 min and then 50 rpm for 2 min, and then 200 rpm of constant agitation speed during the remaining time), rice calli were uniformly entrapped in almost all supports and the immobilization ratio was improved as compared with that using a constant bioreactor operation at 200 rpm. When the inoculum concentration of rice callus was increased, the callus concentration after 7-day culture increased, but the immobilization ratio decreased. To improve the immobilization efficiency further at high cell concentration, the TBR was modified by setting an air sparger inside the stainless mesh cylinder. In the modified TBR, floating of the support by attached air bubbles was avoided, and the immobilization ratio increased further and reached 86.3% when we increased the support volume to 90 ml under the periodic bioreactor operation on a daily basis. The regeneration frequency of immobilized callus was increased by periodic operation and modification of the bioreactor.
Keywords: Rice callus; Turbine blade reactor; Support volume; Periodic operation; Bioreactor modification;

The production of dextransucrase, dextran and fructose by sucrose fermentation using Leuconostoc mesenteroides NRRL-B512(F) was studied in batch operation in a bioreactor with total working volume of 1.5 dm3. The effect of temperature (20 to 40°C), pH (5.5 and 6.7) and sucrose concentration (10 to 120 g/l) on process performance was studied. The optimum conditions for dextran and fructose production were T  = 35°C and pH = 5.5.Cell growth is not inhibited by high sucrose concentrations; however, for sucrose concentration higher than 40 g/dm3 separation of products from cells is difficult.Biomass (X), enzyme (E), dextran (D), fructose (F) and sucrose (S) rate equations were considered in order to derive a simple fermentation kinetic model from batch experimental data. The logistic equation provided a reasonable description for cell concentration, X. The Luedeking and Piret equation was used to describe the enzyme production rate, by considering only the growth associated term. The concentrations of products (dextran and fructose) were reasonably described by a first order kinetic law with respect to both substrate and enzyme concentrations; the substrate, S was consumed for cell growth and for dextran and fructose production.Model parameters μ m and X o were calculated from cell growth as a function of time. The yield Y E/X were calculated from X max and E max and Y X/S was estimated from X max and the sucrose consumed by the bacteria. The remaining parameter k′ was obtained by fitting the experimental data of substrate, dextran and fructose concentrations versus time.
Keywords: Leuconostoc mesenteroides; Dextransucrase; Dextran; Fructose; Batch fermentation; Kinetic; Modelling;

The mass transfer characterization in reversed micellar extraction of amino acid phenylalanine (Phe) is presented. The mass transfer rates in forward extraction of Phe from aqueous KCl solutions (pH 1.4 – 2.3) to AOT/isooctane reversed micellar solutions and in backward extraction from the reversed micellar organic phase to KHCO3/KOH buffer solutions (pH 9.0 – 11.0) were investigated using a stirred cell with a flat liquid–liquid interface. Both the forward and the backward extraction rates are controlled by the interfacial rate processes, i.e., the solubilization and the release processes. The solubilizing rate constants for the forward extraction of Phe increase with decreasing pH and initial Phe concentration and with increasing initial AOT concentration. On the other hand, the releasing rate constants for the backward extraction decrease with increasing initial AOT concentration and with decreasing ionic strength, but are little influenced by pH. The backward extraction rates are fairly slow compared to the forward extraction rates, and are accelerated by the addition of 2-methyl-2-propanol, similar to the extraction of protein lysozyme.
Keywords: Reversed micellar extraction; Solubilization rate; Release rate; Phenylalanine; AOT;

A model for the rate of enzymatic hydrolysis of cellulose in heterogeneous solid–liquid systems by Kamyar Movagarnejad; Morteza Sohrabi; Tahereh Kaghazchi; Farzaneh Vahabzadeh (197-206).
Hydrolysis of cellulose by cellulase enzymes has been studied in a stirred batch reactor at 50°C. A kinetic model has been devised by which the behaviour of such a reaction could be described. The model has been developed on the basis of shrinking particle theory and Langmuir isotherm concept. The applicability of the model has been tested by comparing the experimental results for diverse reaction systems, obtained in the present study or taken from the literature, and those predicted from the model. The degree of agreement was within ±2–11%.
Keywords: Cellulose; Hydrolysis of cellulose; Solid–liquid reactions; Enzyme reactions model; Cellulase enzymes; Shrinking particles model;

This work investigates the enzyme-support equilibrium behaviour in immobilised lipase biocatalysts. Equilibrium data determines the maximum enzyme up-take by unit weight of support. Four lipases were immobilised on two polymeric supports, respectively. They were Lipase PS from Pseudomonas, Lipolase 100L from Humicola, SP871 from Rhizomucor miehel and QL from Alcaligenes. The supports were Accurel EP100 (a polypropylene material) and 45SAA (a polypropylene/silica composite). Experimentally, equilibrium was expressed in terms of lipase loading (LU/g support) versus residual lipase concentration (LU/dm3). Activity, efficiency and operational stability of the immobilised lipases were assayed by solvent-free esterification of oleic acid and octanol.Equilibrium data were modelled by the Langmuir, Freundlich and Redlich–Peterson formulae. It was found that Lipolase 100L/Accurel, PS/45SAA and SP871/45SAA systems conformed to the Langmuir behaviour, while Lipase PS/Accurel and SP871/Accurel systems followed the Freundlich behaviour and Lipolase 100L/45SAA, QL/45SAA and QL/Accurel EP100 resembled Redlich–Peterson behaviour. Whereas immobilisation on Accurel EP100 resulted in classical equilibrium isotherms with all four lipases, immobilisation on support 45SAA resulted in two-plateau equilibrium curves which included a step change in the isotherm for all lipases studied, except for SP871. Quantitatively, for 1 g lipase, Accurel and 45SAA had a maximum capacity of 140 and 260 kLU for PS, 112 and 550 kLU for Lipolase 100L, 320 and 800 kLU for SP871 and 18 and 29 kLU for QL, respectively.
Keywords: Lipase immobilisation; Equilibrium; Hydrophobic; Hydrophilic;

A model of ethanol fermentation by Zymomonas mobilis ATCC 10988 on the medium containing glucose and fructose is proposed. This model was developed on the basis of metabolic analysis and many experimental findings. When glucose was used as the substrate, the dependence of the carbon fraction (α) assimilating to biomass on the specific growth rate (μ) could be well correlated to α  = 0.25μ  + 0.012. This correlation resulted in a novel equation for specific glucose uptake rate, which could describe the Z. mobilis fermentation in both batch and continuous modes. When fructose and glucose were both presented in the liquid medium, the model could predict the uptake of glucose and fructose as well as the formation of biomass, ethanol and sorbitol by Z. mobilis. All parameters used in the model were independently evaluated on the basis of various experimental findings. Good agreement was found between the model predictions and data of Z. mobilis fermentation on media containing both glucose and fructose. The proposed model could also describe the behavior of ethanol fermentation on sucrose medium supplemented with immobilized invertase.
Keywords: Ethanol; Fermentation; Zymomonas mobilis; Modeling; Growth kinetics; Metabolic analysis;

In this study, the competitive biosorption of iron(III) and chromium(VI) to Chlorella vulgaris from a binary metal mixture was investigated in a single-staged batch reactor as a function of V 0/X 0 (volume of solution containing heavy metal mixture/quantity of biosorbent) ratio and second metal ion concentration at pH 2. The obtained results showed that the increase in biomass quantity (or the decrease of V 0/X 0 ratio) with the addition of second metal ion affected the removed quantities of iron(III) or chromium(VI). The sorption phenomenon was expressed by the competitive, multi-component Langmuir adsorption isotherm and this expression was used for calculating each residual or adsorbed metal ion concentration at equilibrium (C eq,i or C ad,eq,i ) at a constant V 0/X 0 ratio for a given combination of heavy metal ions in a single-staged batch reactor. Experimental C eq,i and C ad,eq,i values were compared to those calculated and graphically determined.
Keywords: Binary mixture of iron(III)-chromium(VI); Single-staged biosorption; Chlorella vulgaris;

Economic analysis of lipase production by Penicillium restrictum in solid-state and submerged fermentations by Leda R Castilho; Carla M.S Polato; Edmond A Baruque; Geraldo L Sant’Anna; Denise M.G Freire (239-247).
In the present work an economic analysis of the production of Penicillium restrictum lipase in both submerged (SF) and solid state fermentations (SSF) was performed. For a production scale of 100 m3 lipase concentrate per year, total capital investment needed for the submerged process was 78% higher than that needed for the solid-state fermentation process. The submerged process proved to be economically unfeasible, as unitary product cost was 68% higher than the product selling price. Contrastingly, the solid-state fermentation process turned out to be very attractive from an economic point of view. Also for a scale of 100 m3/year, SSF unitary product cost was 47% lower than the selling price, payback time was 1.5 years, return on investment was 68% and internal return rate was 62% for a 5-year-project life. Furthermore, the profitability of this process remained high even with eventual increases of 40% in product concentration or total capital investment, or decreases of 20% in product price. The great advantage of the SSF process is the extremely cheap raw material it uses as main substrate.
Keywords: Economic analysis; Lipase; Penicillium restrictum; Solid-state fermentation; Submerged culture; Enzyme production;

Index (249).

Index (251-257).