Inactivation of Listeria monocytogenes and Salmonella enterica serovar Senftenberg 775W inoculated into fruit juice by means of ultra high pressure homogenisation

The inactivation of Listeria monocytogenes and Salmonella enterica serovar Senftenberg 775 W by ultra high pressure homogenisation (UHPH) was evaluated in grape and orange juices inoculated at a concentration of approximately 7 log CFU/ml. The fluid inlet temperature used was 6 °C and the pressure levels assayed were 200, 300 and 400 MPa. Viable and injured bacterial counts were obtained 2 h after the UHPH treatments and after 5, 8, and 15 days of storage at 4 °C. Pressure level had a significant impact on the lethal effect of UHPH and complete inactivation of S. enterica serovar Senftenberg 775 W was achieved at 400 MPa. L. monocytogenes showed more resistance than S. enterica serovar Senftenberg 775 W to the UHPH treatments and no significant differences were observed between 300 and 400 MPa treatments in both juices. Sublethal injuries were not detected in any case. During the storage at 4 °C viable counts of both strains showed a decreasing trend. L. monocytogenes viable counts became undetectable in UHPH treated and also in control samples of grape juice which could be attributed to the presence of natural compounds with antilisterial effect.