Effect of high hydrostatic pressure on Listeria innocua 910 CECT inoculated into ewe's milk

Ewe's milk standardized to 6% fat was inoculated with Listeria innocua 910 CECT at a concentration of 10(7) CFU/ml and treated by high hydrostatic pressure. Treatments consisted of combinations of pressure (200, 300, 350, 400, 450, and 500 MPa), temperature (2, 10, 25, and 50 degrees C), and time (5, 10, and 15 min). To determine numbers of L. innocua, listeria selective agar base with listeria selective supplement and plate count agar was used. Low-temperature (2 degrees C) pressurizations produced higher L. innocua inactivation, than treatments at room temperatures (25 degrees C). Pressures between 450 and 500 MPa for 10 to 15 min were needed to achieve reductions of 7 to 8 log units. The kinetics of destruction of L. innocua were first order with D-values of 3.12 min at 2 degrees C and 400 MPa and 4 min at 25 degrees C and 400 MPa. A baroprotective effect of ewe's milk (6% fat) on L. innocua was observed in comparison with other studies using different media and similar pressurization conditions.