Effect of High Hydrostatic Pressure on Listeria innocua 910 CECT Inoculated into Ewe's Milk

Abstract

Ewe's milk standardized to 6% fat was inoculated with Listeria innocua 910 CECT at a concentration of 107 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°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°C) pressurizations produced higher L innocua inactivation than treatments at room temperatures (25°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°C and 400 MPa and 4 min at 25°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.