C. Colby

A Modified Version of the Volume-Averaged Continuum Theory To Predict Pressure Drop across Compressible Packed Beds of Sepharose Big-Beads SP

Using a modified version of the volume‐averaged continuum theory for multiphase processes, theoretical predictions of pressure drop across compressible packed beds of Sepharose Big‐Beads SP (Amrad Pharmacia Biotech, Sydney, Australia) are made. Modifications to the volume‐averaged continuum theory included an additional term incorporated into governing equations to account for the influence of column diameter and a constitutive function to account for the effect of compressibility on pressure gradient. Theoretical predictions are compared to experimental pressure‐drop data. Results indicate the modified volume‐averaged continuum theory can provide accurate pressure‐drop predictions for Sepharose Big‐Beads SP at different bed heights, column diameters, superficial velocities, and fluid viscosity. The influence of column diameter on pressure‐drop behavior during scale‐up is then examined by comparing theoretical predictions for laboratory and production‐scale columns. Predictions demonstrate a significant dependence on column diameter. This result emphasizes the dangers of predicting pressure‐drop behavior for compressible chromatography resins in production‐scale columns by extrapolation from laboratory‐scale pressure‐drop data.

Simulation of compression effects during scaleup of a commercial ion-exchange process

A modified version of the general nonlinear multicomponent rate equation chromatography model has been developed to simulate compression effects on system behavior. It accounts for the variations in porosity and particle deformation that occur within a packed bed during compression. This paper investigates the effect of compression on the scaleup of a commercial packed‐bed ion‐exchange process to manufacture a whey growth factor extract (WGFE). The resin employed in the ion‐exchange process is Sepharose Big‐Beads SP (Amrad‐Pharmacia, Sydney, Australia). Compression‐induced changes in packed‐bed porosity and particle diameter for a laboratory‐ (2 cm) and a production‐scale (20 cm) column were estimated from pressure‐drop data by using a modified volume‐averaged continuum theory. These were combined with model parameters from a previous experimental study for two major whey proteins, lactoperoxidase and lactoferrin. Model simulations were performed. First, model parameters were validated by replication of experimental frontal adsorption breakthrough and step‐elution curves. Selection of numerical parameters and accurate adsorption equilibria were identified as critical steps in ensuring successful reconciliation of model predictions with experimental data. The effect of compression on frontal adsorption and elution steps during scaleup was then investigated. For both frontal adsorption and step elution, system behavior was found to be largely independent of compression. Increased compression created only minor and trivial variations in effluent concentration profiles. These were influenced by two competing mechanisms, namely, premature breakthrough and increased external film mass transfer. Further simulations with a smaller particle size and superficial velocity displayed no significant increase in compression effects. Compression effects are not important during scaleup of this system.

Optimal Conditions for Controlling Haze-Forming Wine Protein with Bentonite Treatment: Investigation of Matrix Effects and Interactions Using a Factorial Design

Protein instability in white wine can result in unsightly haze formation, and therefore, its prevention by adsorption of haze proteins onto bentonite is an important unit operation in commercial wine production. Optimisation of this process is challenging due to the performance impact of environmental factors and matrix effects which are difficult to control and study in wine systems. These issues are addressed in the present study; the effect of different factors on adsorption behaviour of a purified thaumatin-like grape protein (VVTL1) by sodium bentonite in a chemically defined model wine solution was investigated using a factorial design with surface response analysis. Bentonite adsorption of VVTL1 was well characterised by a multi-factor Langmuir adsorption model. The main effects of pH, temperature, potassium concentration as well as the pH*potassium matrix interaction all had a significant effect (p < 0.05) on the adsorption capacity, as did the aging of bentonite slurry before use. Observations support the hypothesis that VVTL1 adsorption onto sodium bentonite is affected by steric mass action and local interactions of exposed protein charge, with pH and temperature effects related to changes in protein conformation under those conditions. Variation in potassium concentration can cause similar effects and influence adsorption capacity by affecting bentonite swelling and charge potential, providing a greater surface area for adsorption. From a processing perspective, results suggest bentonite treatment efficiency will be optimised by treating wines at higher temperatures rather than during cold storage, at the lower pH and before cold (tartrate) stabilisation.

Ensuring oxygenation of carrot cell cultures in a Couette viscometer during investigation of shear effects

Mathematical simulation and experimental measurement of dissolved O2 were performed for extended (up to 8 h) shear testing of Daucus carota (carrot) cell cultures in a conventional Couette viscometer (0.625 mm annulus). The results suggest O2 depletion below critical levels for cell growth may occur. A novel design modification incorporating an O2-permeable silicone-layer spun cast on a porous ceramic bowl was devised. It significantly improved oxygenation of the cell cultures, keeping dissolved O2 near saturation.