EFFECT OF ATTACHMENT TIME FOLLOWED BY CHLORINE WASHING ON THE SURVIVAL OF INOCULATED LISTERIA MONOCYTOGENES ON TOMATOES AND SPINACH

The effect of attachment time (30 min, 24, 48 and 72 h) followed by chlorine washing (200 ppm) on the survival of inoculated Listeria monocytogenes on the surface and subsurface of tomatoes and spinach were studied. The work was done to determine the efficacy of chlorine to decontaminate surface and subsurface pathogens that may have come into contact with produce during preharvest. Tomatoes and spinach leaves were inoculated with a 6 log cfu/mL 18 h culture of L. monocytogenes ATCC 7644 (LM) on the surface and subsurface and incubated at 20C for either, 30 min, 24, 48 or 72 h. LM attached and survived on the surface and subsurface structures of both control and chlorine-washed vegetables after each attachment time, up to 72 h. Higher levels of LM attachment and survival was however noticed on the subsurface structures. Chlorine had a greater effect on the LM on the surface structures compared to those in the subsurface structures, possibly because chlorine was not able to access the subsurface structures where the pathogens were located. Chlorine was not effective in totally inactivating the surface LM on spinach and tomato. This research indicated that LM could attach to both surface and subsurface structures of both tomatoes and spinach within 30 min and that even after 72 h, it still remained viable. PRACTICAL APPLICATIONS This study will inform the produce industry on the ability of L. monocytogenes ATCC 7644 to attach and grow on the surface and subsurface structures of tomato and spinach during post harvest. More attention should be given to this phenomenon because the use of fresh or minimally processed fruits and vegetables are recommended as part of a healthy diet. It also indicates that minimal processors should avoid using vegetables with wounds since L. monocytogenes attached more to the subsurfaces structures of the produce. Moreover, the use of sanitizers such as chlorine is less effective under these conditions. It has also brought to light the inability of chlorine to effectively decontaminate pathogens making it imperative for the produce industry to implement Hazard Analysis Critical Control Point, Good Agricultural Practice and Good Hygiene Practice.