Inactivation of Escherichia coli and Listeria monocytogenes on iceberg lettuce by dip wash treatments with organic acids

Aims: To study and compare the efficacy of organic acids and chlorine dipping in inactivation of Escherichia coli and Listeria monocytogenes on fresh-cut iceberg lettuce. Methods and Results: Fresh-cut iceberg lettuce leaves were inoculated with E. coli or L. monocytogenes. After inoculation, samples were stored at 4 degrees C for 24 h and dipped in organic acid or chlorine solutions for 2 and 5 min. E. coli and L. monocytogenes were enumerated on selective media. Treatment of fresh-cut iceberg lettuce with chlorine solution caused 1.0 and 2.0 log(10) CFU g(-1) reductions in the number of L. monocytogenes and E. coli, respectively. Maximum reduction for E. coli (about 2.0 log(10) CFU g(-1)) was obtained for samples dipped in lactic or citric acids while maximum reduction for L. monocytogenes (about 1.5 log(10) CFU g(-1)) was attained for samples dipped in lactic acid. Conclusions: Dipping of iceberg lettuce in 0.5% citric acid or 0.5% lactic acid solution for 2 min could be as effective as chlorine for reducing microbial populations on fresh-cut iceberg lettuce. Significance and Impact of the Study: Dipping in solutions containing organic acids is shown to be effective to reduce E. coli and L. monocytogenes on fresh-cut iceberg lettuce.