Biochemical Engineering Journal (v.4, #2)

Bioreactors for plant engineering: an outlook for further research by Lidija Sajc; Dragan Grubisic; Gordana Vunjak-Novakovic (89-99).
This paper reviews bioreactor related aspects of large scale plant cell technology for the production of biologically active compounds. Bioreactor designs currently in use are discussed with respect to specific operating parameters that can be varied to modulate cell growth and function in order to optimize product release and separation. Flow and mixing are recognized as key factors responsible for both the direct hydrodynamic effects on cell shape and function and flow induced changes in mass transfer of nutrients and metabolites. The integration of biosynthesis and separation is considered as a possible approach towards more efficient plant cell and tissue culture.
Keywords: Plant cell bioreactors; Plant cell culture; Mixing; Bioseparations;

Separation of glucose/fructose mixtures: counter-current adsorption system by Lj. Matijašević; Đ. Vasić-Rački (101-106).
In the present study a simulated counter current adsorption system was used to separate two components with different adsorption selectivity. The system consists of four columns connected in series, packed with Lewatit MDS 1368. The mathematical model was developed to calculate concentration profiles in the adsorbers where the adsorption isotherms were presented by linear equations. Concentration profiles were calculated from a dispersed flow model. On the basis of this model a theoretical system analysis was carried out showing that there is an optimal ratio of process parameters (feed/eluent) where the effectiveness of separation in counter current adsorption system can be improved.
Keywords: Adsorption isotherms; Counter-current system; Glucose/fructose separation;

Effect of solution conditions on protein damage in foam by J.R Clarkson; Z.F Cui; R.C Darton (107-114).
In this study we investigated the conditions under which protein damage during foaming could be reduced. We used bovine serum albumin (BSA), immunoglobulin G (IgG), pepsin, catalase and lysozyme. The parameters examined were ionic strength, pH, protein concentration and the addition of sugars (trehalose and sucrose). Results showed that protein damage can be reduced by operating at optimal ionic strength and pH, and to a lesser extent, by the addition of sugars. Solution conditions under which the native structure of the protein was stabilised in solution favoured a reduction in the amount of damage, due to lower surface adsorption. The actual quantity of protein damaged in foaming was found to be relatively insensitive to changes in the bulk protein concentration, provided that the concentration was near to, or greater than, the apparent CMC value.
Keywords: Biophysical chemistry; Bubble columns; Enzyme deactivation; Protein denaturation; Foam; Ionic strength;

The chitinase fermentation process utilizing chitin as the sole carbon source was investigated in a stirred tank bioreactor. Agitator speed of 224 rpm was found to be most suitable for cell growth as well as for chitinase production. Chitinase yield decreased rapidly at higher agitator speed, while decrease in cell yield at higher agitator speed was not rapid. Probably, mass transfer limitation was predominant in the fermentation process at lower agitator speed. Higher agitator speed appears to reduce chitinase production.
Keywords: Agitation; Bioreactors; Chitinase; Kinetics; Trichoderma harzianum; Yield;

The batch fermentations were conducted using lactose as the substrate at pH 6.5 and temperature 30°C. Average batch kinetic data was eventually used to develop an unstructured mathematical model. The kinetic parameters of the model were determined by non-linear regression technique using the batch experimental results. Parametric sensitivity analysis showed the maximum specific substrate consumption rate (r S max) and the maintenance energy constant (m S) to be the most sensitive parameters. The experimental observations in batch fermentation were close to the model predictions. The batch model was extrapolated to identify nutrient feeding strategies, which were tested successfully for two different fed-batch fermentations. It demonstrated enhanced propionic acid productivity. The developed model was found suitable for the design of feeding strategies to increase propionic acid production in fed-batch mode of reactor operation.
Keywords: Batch/fed-batch propionic acid fermentation; Modelling of kinetics;

In this paper, hydrodynamic modelling of a fluidised bed reactor is studied through two different approaches (the input/output model and the distributed parameters model), as the aim of our work is complete study of anaerobic digestion in a fluidised bed reactor. After identification of parameters based on several experiments, the use of each model is discussed according to the stated objectives. Orthogonal collocation is used to reduce the partial derivative equations and the resulting model is validated for all our experiments. We show that the axial dispersion model appears to be the best choice in our case to design a control law for the process. The different steps we followed during this study, enable us to model recycling outside the reactor in a very simple and satisfactory way.

Cellulase deactivation in a stirred reactor by K. Ganesh; J.B. Joshi; S.B. Sawant (137-141).
During the production or downstream processing of an enzyme it is always subjected to shear stress, which may deactivate the enzyme. This susceptibility of enzymes to shear stress is a major concern as it leads to the loss of enzyme activity and is, therefore, a major consideration in the design of the processes involving enzyme production and its application.In the present work the cellulase enzyme was subjected to shear stress in a stirred reactor with an objective of investigating its deactivation under various conditions such as different agitation speeds, concentrations of enzyme, concentrations of buffer, pH ranges, buffer systems and the presence of gas–liquid interface. It was found that the extent of deactivation depends upon the conditions under which the enzyme was subjected to shear.
Keywords: Cellulase; Deactivation; Gas sparging; Surface aeration; Surface deactivation;

N-(benzyloxycarbonyl)-L-aspartyl-L-phenylalanine methyl ester (ZAPM), an aspartame precursor, was synthesized enzymatically from N-(benzyloxycarbonyl)-L-aspartic acid (ZA) and L-phenylalanine methyl ester (PM) using a biphasic reaction system. Measurement of the partition coefficient in an aqueous/alcohol system showed that, 1-hexanol and 1-heptanol were proper solvents for the system. The membrane phase separation could be performed using a hydrophobic membrane, and 1-hexanol gave higher flux than 1-heptanol. Integration of the membrane phase separation into the biphasic enzyme reaction system was realized by the continuous stable ZAPM production.
Keywords: Biphasic reaction; Phase separation; Hydrophobic membrane; Enzyme reactor; Aspartame precursor;

Selective separation of chymotrypsinogen using anti-chymotrypsinogen-antibodies as affinity ligands was realized in reverse micellar system composed of a nonionic surfactant tetra-oxyethylenemonodecylether. Antibodies as affinity ligands were immobilized in reverse micelles by combining cholesteryl groups covalently. Selective separation of proteins using bioaffinity ligands was extended to antigen-antibody reaction system, which enables us to choose any kind of target proteins.
Keywords: Antigen-antibody interaction; Reverse micellar system; Chymotrypsinogen; Extraction; Nonionic surfactant;

Growth profiles of the batch and fed-batch culture of hybridoma cells producing monoclonal antibody were simulated using an unstructured model. The model describes the production of cellular macromolecules and monoclonal antibody, the metabolism of glucose and glutamine with the production of lactate and ammonia, and the profiles of cell growth in batch and fed-batch culture. Equations describing the cells arrested in G1 phase [T.I. Linardos, N. Kalogerakis, L.A. Behie, Biotechnol. Bioeng. 40 (1992) 359–368; E. Suzuki, D.F. Ollis, Biotechnol. Bioeng. 34 (1989) 1398–1402] were included in this model to describe the increase of the specific antibody productivity in the near-zero specific growth rate, which was observed in the recent experiments in fed-batch cultures of this study and the semi-continuous culture of hybridoma cells [S. Reuveny, D. Velez, L. Miller, J.D. Macmillan, J. Immnol. Methods 86 (1986) 61–69]. This model predicted the increase of specific antibody production rate and the decline of the specific production rate of cellular macromolecules such as DNA, RNA, protein, and polysaccharide in the late exponential and decline phase of batch culture and at lower specific growth rates in the fed-batch culture.
Keywords: Unstructured model; Hybridoma; Monoclonal antibody; Growth phase; Macromolecule;