Ozone inactivation of acid stressed Listeria monocytogenes and Listeria innocua in orange juice using a bubble column

Orange juice inoculated with Listeria monocytogenes strains ATCC 7644, NCTC 11994 and Listeria innocua NCTC 11288 (10⁶ CFU/ml) as challenge microorganisms was treated with direct ozone at 0.098 mg/min/ ml for different time periods (0-8 min) using an ozone bubble column. Ozone treatment of mild acid stressed and mild acid stress-habituated (pH 5.5) cells of L. monocytogenes resulted in higher inactivation times compared to control non-acid stressed cells. Additionally acid stressed cells habituated in orange juice (ATCC 7644 & NCTC 11288), showed higher inactivation times during ozonation by comparison with the control as well as the mild-acid stressed cells. Overall the gaseous ozone treatment applied to orange juice resulted in a population reduction of 5 log cycles within a time range that varied between 5 and 9 min.