The effects of various disinfectants against Listeria monocytogenes on fresh-cut vegetables

Demand for fresh, healthier convenience-type foods has stimulated sales of fresh-cut vegetables in North America. As part of an overall program to better define the microbiological safety of these products, studies were done to examine the effects of various disinfectants against Listeria monocytogenes on fresh-cut vegetables. Some of the more established disinfectants such as chlorine and chlorine dioxide, as well as some of the newer ones including Salmide(R) and trisodium phosphate were tested against L. monocytogenes on lettuce and cabbage. Different exposure times, as well as concentrations of the disinfectants were evaluated. In addition, organic acids such as lactic and acetic were examined for their ability to inactivate L. monocytogenes present on the surface of vegetables. Chlorine was also tested in combination with the organic acids and various surfactants. For chlorine (200 ppm, 10 min) the maximum observed log(10) reduction of L. monocytogenes at 4 and 22 degrees C, respectively, was 1.3 and 1.7 for lettuce and 0.9 and 1.2 for cabbage. Chlorine dioxide treatment (5 ppm, 10 min) of lettuce and cabbage at 4 and 22 degrees C, respectively, resulted in a maximum observed log(10) reduction of L. monocytogenes of 1.1 and 0.8 for lettuce and 0.4 and 0.8 for cabbage. In comparison, the highest levels of Salmide(R) used on cabbage and lettuce (200 ppm) at 22 degrees C led to maximum reductions of 1.8 and 0.6 logs, respectively None of the surfactants tested improved the disinfectant efficiency of chlorine, and actually proved to be antagonistic. Trisodium phosphate had almost no effect on reducing numbers of L. monocytogenes, at levels that did not affect the organoleptic qualify of lettuce. Lactic acid proved to be more effective than acetic acid in reducing numbers of L. monocytogenes, although maximum reductions of only 0.5 and 0.2 logs were observed after a 10 min exposure to 1% solutions of each organic acid. In general, therefore, one can expect approximately a 1 log reduction in numbers of L. monocytogenes, regardless of the disinfectant used. (C) 1996 Academic Press Limited