Effect of residual chlorine and organic acids on survival and attachment of Escherichia coli O157: H7 and Listeria monocytogenes on spinach leaves during storage

The use of sanitizers during produce wash operation is a common practice, but little is known about the effect of residual sanitizers on minimizing food safety risks associated with post-sanitizing cross-contaminations. This study investigated the effect of residual chlorine and organic acids on the survival and the attachment of E. coli O157:H7 and L. monocytogenes on spinach leaves during refrigerated storage. The pathogens were spot inoculated on chlorine (100 ppm), lactic acid (0.5%) and acetic acid (0.5%) treated leaves, and their survival during refrigerated storage (4 degrees C) was examined. A significant reduction (P < 0.05) in E. coli O157:H7 and L. monocytogenes populations was observed within 15 min of exposure on chlorine-treated leaves, with total reductions of 2.64 and 3.15 log CFU/cm(2) respectively after 48 h. On 0.5% lactic acid treated leaves, the reduction in E. coli O157:H7 and L. monocytogenes population was 3.07 log CFU/cm(2) (24 h) and 1.40 log CFU/cm(2) (48 h), respectively. The effect of residual sanitizers was significantly greater on loosely attached populations compared to strongly attached populations. These results indicate that the residual sanitizers present on vegetable leaves after sanitizers wash may have a role in reducing the risks associated with post-sanitizing cross-contamination.