Combining High-Pressure Processing and Supercritical Carbon Dioxide for Inactivation of Listeria innocua .

The effect of high-pressure treatment with supercritical CO 2 on the inactivation of Listeria innocua in a fish soup was investigated. The soup was inoculated with L. innocua , packaged in modified atmosphere with 50:50 or 95:5 CO 2 :N 2 , high-pressure processed (300, 350, 400 and 600 MPa, 2 min) under subcritical (T < 304 K) or supercritical conditions (T > 304 K) and stored at 4 °C for up to 53 days. Treatment at 400 and 600 MPa had a significant ( p < 0.05) effect on L. innocua under both supercritical and subcritical conditions. In contrast, pressurization at 350 MPa and supercritical conditions were needed to significantly ( p < 0.05) inactive L. innocua . Increased levels of CO 2 in the headspace significantly ( p < 0.05) reduced the bacterial load during processing, and supercritical conditions had a significant ( p < 0.01) interaction with both CO 2 levels and pressure. Increased storage time gave significantly increased levels of L. innocua at 400 and 600 MPa. In addition, high levels of CO 2 significantly decreased ( p < 0.001) growth. However, 350 MPa under supercritical conditions seemed to set the L. innocua in a permanent lag phase, with slow and steadily decreasing numbers of bacteria during storage. All the design variables resulted in significant inactivation of L. innocua , and supercritical conditions combined with high levels of CO 2 inhibited the recovery of L. innocua to a large degree.