Effect of compressed carbon dioxide on microbial cell viability

In order to study the influence of compressed carbon dioxide, over a range of pressures (1.5 to 5.5 MPa) and exposure times (up to 7 h), on the surviv al of Escherichia coli, Saccharomyces cerevisiae, and Enterococcus faecalis , a new pressurizable reactor system was conceived. Microbial cells were in oculated onto a solid hydrophilic medium and treated at room temperature; t heir sensitivities to inactivation varied greatly. The CO2 treatment had an enhanced efficiency in cell destruction when the pressure and the duration of exposure were increased. The effects of these parameters on the loss of viability was also studied by response-surface methodology. This study sho wed that a linear correlation exists between microbial inactivation and CO2 pressure and exposure time, and in it models were proposed which were adeq uate to predict the experimental values. The end point acidity was measured for all the samples in order to understand the mechanism of microbial inac tivation. The pHs of the treated samples did not vary, regardless of the ex perimental conditions. Other parameters, such as water content and pressure release time, were also investigated.