Effect of Supercritical Carbon Dioxide on Some Bacteria and Yeasts of Interest in the Food Industry

The sterilisation with supercritical carbon dioxide of some microorganisms of interest in food technology is considered as a first step for the application of this technique to complex media on a large scale. A sourdough yeast strain and several bacterial species (Enterococcus faecium, Escherichia coli andLactobacillus casei) are treated with supercritical carbon dioxide in a static system. Experiments are performed at a temperature of 313 K, at different pH values (6.4 and 7.4), different pressures (10 and 20 MPa) and several times of exposition at the operating conditions (20, 40, 60, 80 min). It is found that E. coli and E. faecium are more sensitive to the treatment than L. casei and sourdough yeast. The effect is enhanced at a pH value of 6.4 for each pressure/time combination and stronger inactivation is obtained by increasing the exposition time and pressure. Nevertheless, a similar inactivation can be achieved with both 20 MPa+60 min and 10MPa+80min in buffer at pH=6.4; the latter are relatively mild conditions in view of possible industrial applications.