EFFECT OF HIGH HYDROSTATIC-PRESSURE ON LISTERIA-INNOCUA-910 CECT INOCULATED INTO EWE 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 hydro static pressure. Treatments consisted of combinations of pressure (200 , 300, 350, 400, 450, and 500 MPa), temperature (2, 10, 25, and 50 deg rees C), and time (5, 10, and 15 min). To determine numbers of L. inno cua, listeria selective agar base with listeria selective supplement a nd plate count agar was used. Low-temperature (2 degrees C) pressuriza tions 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 o f 3.12 min at 2 degrees C and 400 MPa and 4 min at 25 degrees C and 40 0 MPa. A baroprotective effect of ewe's milk (6% fat) on L. innocua wa s observed in comparison with other studies using different media and similar pressurization conditions.