Effectiveness of electrolyzed water on the inactivation of Listeria monocytogenes in letucce (lactuca sativa L.)

The effectiveness of electrolyzed oxidizing water for inactivating L. monocytogenes in suspension and inoculated in lettuce was evaluated. An electrolytic cell for the production of EO water was built and a solution of 5% NaCl was used. The EO water produced had a residual chlorine concentration of 29 parts per million (ppm) and pH 2.83. Ten strains of L. monocytogenes isolated from processed chicken (109 CFU/ml) were inoculated on 9 ml of EO water or 9 ml of deionized water (control) and incubated at 15°C for 5, 10, 15 and 20 min. The surviving population of each strain was determined on Columbia agar. An exposure time of 5 min reduced the populations by approximately 6.6 log CFU/ml. The most resistant strains to hypochlorite (NaOCl) were selected and used in a strain mixture (9.56 log CFU/ml, 109UFC/ml approximately) for the inoculation of 35 lettuces by the dip inoculation method using distilled water as control. The population mean of L. monocytogenes after treatment with EO water and distilled water was reduced by 3.92 and 2.46 log CFU/ml respectively (p= 0.00001). EO water and 6% acetic acid (vinegar) were combined for improve the EO water effect on L. monocytogenes inoculated in lettuce, the effectiveness of this combination were examined. The results showed that there was a synergistic effect of both antimicrobial agents (population reduction by 5.49 log CFU/ml approximately) on the viability of L. monocytogenes cells.