Sterilization and Preservation in Bioprocessing

  • Owen P. Ward


Sterilization technology is used in bioprocessing to produce culture media, air and other processing materials, foods and pharmaceuticals which are free from living organisms as ascertained by defined testing procedures. Sterilization procedures include the use of dry heat, steam, gas, ionizing radiation, filtration, and the use of liquid and other sterilization materials. Apart from filtration, the remaining techniques involve the destruction of micro-organisms. The rate of destruction of microbial cells is logarithmic, that is, first order with respect to the concentration of cells; it can be described by the expression
$$\frac{{{N_0}}}{{{N_t}}} = {e^{kt}}$$
where N t = the number of organisms alive at time t
$$ \begin{gathered} N_0 = {\text{ the initial number of organisms}} \hfill \\ {\text{k = the kinetic rate constant}} \hfill \\ \end{gathered} $$
As N t approaches infinity. According to this equation, absolute sterility is impossible to attain and, in practice, total kill is assumed when defined acceptable tests at culturing result in no growth. Because the sterilization rate is a function of microbial cell concentration, ‘bioburden or bioload’ (the number of micro-organisms present) is taken into account in designing industrial sterilization cycles. Typical death rates for E. coli at various temperatures are illustrated in Fig. 5.1


Fumaric Acid Propyl Gallate Sorbic Acid Steam Injection Steam Sterilization 
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Further reading

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Copyright information

© Owen P. Ward 1991

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  • Owen P. Ward

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