Efficacy of Ozone on Microbial Quality and Reduction of Inoculated of E. coli O157:H7 and Salmonella on Leaf Lettuce

Ozone is a strong oxidant and a potent disinfecting agent. There are numerous application areas of ozone in food industry. While there are many investigations on the application of ozone in food industry, relatively little information is available on the potential of ozone to reduce microbial populations in fresh-cut fruits and vegetables and the visual quality of lettuce. In this study, ozone water was applied at five concentrations (0.6, 0.8, 1.2, 1.6 and 2 ppm) for four exposure times (1, 3, 5 and 10 min) on natural microflora and E. coli O157:H7 and Salmonella inoculated of lettuce. The reduction in the total bacterial count, yeast and mold, total coliform, as well as lactic acid bacteria counts were examined. The promising results indicated the efficacy of ozone water to reduce the microbial populations on lettuce. In the best condition, the inoculated samples of E. coli O157:H7 (ATCC 35150, NCTC 12900), Salmonella typhi morium (ATCC 14028, NCTC 12023) and Salmonella enterica subsp, enterica (PTCC 1709) on lettuce were decreased further than 2 log10 cfu/g. The results showed the population of aerobic mesophilic bacteria, yeast/ moulds, total coliforms and lactic acid bacteria were decreased to 1.54, 0.94, 1.94 and 1.35 log10 cfu/g respectively. The method of ozone generation, type of application, as well as the optimal exposure time and concentration of ozone as an antimicrobial agent on lettuce is mentioned in detail.