Inactivation of Escherichia coil O157 : H7, Listeria monocytogenes, and Lactobacillus leichmannii by combinations of ozone and pulsed electric field

Pulsed electric field (PEF) and ozone technologies are nonthermal processin g methods with potential applications in the food industry. This research w as performed to explore the potential synergy between ozone and PEF treatme nts against selected foodborne bacteria. Cells of Lactobacillus leichmannii ATCC 4797, Escherichia coli O157:H7 ATCC 35150, and Listeria monocytogenes Scott A were suspended in 0.1% NaCl and treated with ozone, PEF, and ozone plus PEF Cells were treated with 0.25 to 1.00 mug of ozone per ml of cell suspension, PEF at 10 to 30 kV/cm, and selected combinations of ozone and P EF Synergy between ozone and PEF varied with the treatment level and the ba cterium treated. L. leichmannii treated with PEF (20 kV/cm) after exposure to 0.75 and 1.00 mug/ml of ozone was inactivated by 7.1 and 7.2 log(10) CFU /ml, respectively; however, ozone at 0.75 and 1.00 mug/ml and PEF at 20 kV/ cm inactivated 2.2, 3.6, and 1.3 log(10) CFU/ml, respectively. Similarly, o zone at 0.5 and 0.75 mug/ml inactivated 0.5 and 1.8 log(10) CFU/ml of E. co li, PEF at 15 kV/cm inactivated 1.8 log(10) CFU/ mi, and ozone at 0.5 and 0 .75 mug/ml followed by PEF (15 kV/cm) inactivated 2.9 and 3.6 log(10) CFU/m l, respectively. Populations of L. monocytogenes decreased 0.1, 0.5, 3.0, 3 .9, and 0.8 log(10) CFU/ml when treated with 0.25, 0.5, 0.75, and 1.0 mug/m l of ozone and PEF (15 kV/cm), respectively; however, when the bacterium wa s treated with 15 kV/cm, after exposure to 0.25, 0.5, and 0.75 mug/ml of oz one, 1.7, 2.0, and 3.9 log(10) CFU/ml were killed, respectively. In conclus ion, exposure of L. leichmannii, E. coli, and L. monocytogenes to ozone fol lowed by the PEF treatment showed a synergistic bactericidal effect. This s ynergy was most apparent with mild doses of ozone against L. leichmannii.