Siddiqi, Somaiya Fatima; (1998) Process simulation and optimisation of high pressure disruption for the release of intracellular proteins. Doctoral thesis (Ph.D), UCL (University College London).

Text Process_simulation_and_optimis.pdf Download (21MB)

Abstract

The aim of this study was to simulate high pressure homogenisation and to examine the use of simulation techniques in identifying optimal strategies for integrating this unit operation with the fermentation process. The first part of this thesis describes the models developed to predict changes in homogenate particle size distributions (PSDs) generated during the high pressure homogenisation of packed baker's yeast Saccharomyces cerevisiae. The influence of homogenisation conditions on the value of d50, where d50 is the particle size below (or above) which 50% of the particles in the total PSD lie, is explained using the following mathematical expression: ln[d50,N=0 / (d50,N=0 - d50)]=kD N^β ΔP^α where, d50,N=0 is the d50 value for the whole cells, N is the number of passes; ΔP=(P - Pth), P is the operating pressure , Pth is the threshold pressure i.e. the pressure below which there is no significant cell disruption occurring, kD is a rate constant and; β and α are the exponents of N and ΔP, respectively. For baker’s yeast the value of β was found to be -0.4 and the value of α was found to be -1. A Boltzman-type equation was then found to predict the total PSD using d50 as an input parameter. The second part of this thesis details work carried out to deduce whether the scale of high pressure homogeniser used has any effect on the cell disruption process. It was found that for the production scale, pilot scale and small scale homogenisers tested, packed baker's yeast cell disruption kinetics was independent of homogeniser capacity. A study was also carried out to deduce the effect of initial cell concentration on cell disruption characteristics using high pressure homogenisation. It was found that cell disruption characteristics were independent of initial cell concentrations between the range of 1 - 45% wet cell weight/ L for packed baker's yeast. The above results were then used to define a scaled-down cell disruption process. This scaled-down process can now be used in process verification studies of large scale processes. The final part of this thesis describes the impact of fermentation and processing conditions on the disruption of baker's yeast. It was found that cell cultures grown using high dilution rates, defined media, aerobic growth conditions, or harvested during early growth phase were more susceptible to disruption than cell cultures grown using low dilution rates, complex media, anaerobic growth conditions or harvested during late growth phase. It was also found that cell cultures that were stored at 4°C post harvesting became more resistant to disruption with time. This interaction between the fermentation process conditions on the cell disruption unit operation was modelled. It was found that there is a linear relationship (regression coefficient >0.94) between the cell disruption rate constant kD and the initial whole cell d50 (i.e. d50,N=0), irrespective of growth rate, growth phase and storage time but not irrespective of growth media. A weaker linear relationship (regression coefficient = 0.79) between the cell disruption rate constant kD and the initial whole cell d50 (i.e. d50,N=0) was found, irrespective of growth media, growth rate, growth phase and storage time. These linear models give reasonable first approximations of kD given only the initial d50 value of the whole cell culture PSD and provide a convenient quantitative measure of the effect of changing upstream fermentation conditions on the subsequent stage of high pressure homogenisation. Cell disruption results obtained were also used to elucidate the mechanism of high pressure homogenisation. It was found that the mechanism of high pressure homogenisation is not due to forces generated by turbulence.

Download activity - last month

Export as JSONXMLCSV

Download activity - last 12 months

Export as JSONCSVXML

Downloads by country - last 12 months

Export as CSVXMLJSON

Archive Staff Only

View Item