THE EFFECTS OF VARIOUS DISINFECTANTS AGAINST LISTERIA-MONOCYTOGENES ON FRESH-CUT VEGETABLES

Demand for fresh, healthier convenience-type foods has stimulated sale s of fresh-cut vegetables in North America. As part of an overall prog ram to better define the microbiological safety of these products, stu dies were done to examine the effects of various disinfectants against Listeria monocytogenes on fresh-cut vegetables. Some of the more esta blished disinfectants such as chlorine and chlorine dioxide, as well a s 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 e valuated. In addition, organic acids such as lactic and acetic were ex amined for their ability to inactivate L. monocytogenes present on the surface of vegetables. Chlorine was also tested in combination with t he organic acids and various surfactants. For chlorine (200 ppm, 10 mi n) 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 let tuce 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 su rfactants 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 no t affect the organoleptic qualify of lettuce. Lactic acid proved to be more effective than acetic acid in reducing numbers of L. monocytogen es, 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 gene ral, therefore, one can expect approximately a 1 log reduction in numb ers of L. monocytogenes, regardless of the disinfectant used. (C) 1996 Academic Press Limited