High-pressure and thermal-assisted pasteurization of habituated, wild-type, and pressure-stressed Listeria monocytogenes, Listeria innocua, and Staphylococcus aureus

Current study investigated decontamination efficacy of elevated hydrostatic pressure against wild-type, 72-h habituated, and pressure-stressed phenotypes of Listeria monocytogenes, Listeria innocua, and Staphylococcus aureus in milk and orange juice. Pressure intensity levels of 350 and 500 MPa were utilized at 4.4 degrees C and 60.0 degrees C for up to 7 min. Temperature was controlled using a stainless steel water jacket surrounding reaction chamber connected to a refrigerated circulating water bath. Results were statistically analyzed using ANOVA. While <2 log reduction of L. monocytogenes, L. innocua, and S. aureus were observed after treatments of up to 7 min at 500 MPa at 4.4 degrees C, same treatment at 60.0 degrees C resulted in >= 5 log reductions (p < 0.05) of pathogens in milk. Similar trends were observed when the pathogens were inoculated in acidic environment of orange juice and treated at 350 MPa at 4.4 and 60 degrees C. As such, under the conditions of our experiments, we observed that mild heat could to great extend augment the efficacy of a pressure-based pasteurization treatment. The three phenotypes (habituated, wild-type, and pressure-stressed) of these Gram-positive pathogens exhibited comparable sensitivity to treatments, indicating a validated treatment against wild-type cells could be as efficacious against other phenotypes as well.