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An ultra scale-down study to understand and predict E. coli cell recovery from high-speed discharge centrifuges.

Chan, G.H.T.; (2006) An ultra scale-down study to understand and predict E. coli cell recovery from high-speed discharge centrifuges. Doctoral thesis , University of London. Green open access

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The ability to recover cells from a fermentation broth in an intact form can be an important criterion for determining the overall performance of a recovery and purification sequence. Disruption of the cells can lead to undesired contamination of an extracellular product with intracellular components and vice versa loss of intracellular products may occur. In particular, the value of directed location of a product in the periplasmic space of say Escherichia coli would be diminished by such premature non-selective cell disruption. Several options exist for cell recovery or removal namely centrifugation, in a batch or a continuous configuration, filtration or membrane operations, and in selected cases expanded beds. The choice of operation is dependant on many variables including the impact on the overall process sequence. In all cases the cells are exposed to shear stresses of varying levels and times and additionally such environments exist in ancillary operations such as pumping, pipe flow and control valves. In this thesis an ultra scale-down device has been designed to expose cells to controlled levels of shear, time and impact in a way that seeks to mimic those effects that may occur during full-scale processes using continuous or intermittent discharge disc stack centrifuges. Results demonstrate that the extent of cell breakage was found to be proportional to shear stress. An additional level of breakage occurred due to the jet impacting on the collecting surface. Here it was possible to correlate the additional breakage with the impact velocity, which is a function of the distance that the jet travels before impacting on the collection surface, and the initial jet velocity. The accuracy of the ultra scale-down predictions has been tested using two scales of intermittent discharge disc-stack centrifuges. After the calibration of the ultra scale- down device using cells of a standard preparation the mimic gave a similar trend of cell breakage to that observed at large-scale. However the error margins for the mimic was up to +1-20% and hence further work is required to refine the mimic and further understanding of the calibration factor is necessary. In addition, an initial understanding of the effect of change of centrifuge geometry and method of operation on the level of cell damage was gained. Finally, the extent of damage as represented by protein release is shown to be indicative of even greater extents of damage with studies using flow cytometry showing significant changes in cell wall structure.

Type: Thesis (Doctoral)
Title: An ultra scale-down study to understand and predict E. coli cell recovery from high-speed discharge centrifuges.
Identifier: PQ ETD:592707
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by Proquest
UCL classification:
URI: https://discovery.ucl.ac.uk/id/eprint/1445387
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