Abstract:
The effect of attachment time (30 min, 24, 48 & 72 h) followed by chlorine washing
(200 ppm) on the survival of inoculated Listeria monocytogenes on the surface and
sub-surface of tomatoes and spinach were studied. The work was done to determine
the efficacy of chlorine to decontaminate surface and sub-surface pathogens that may
have come into contact with produce during pre-harvest. 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 sub-surface and incubated at 20 oC for either, 30 min, 24, 48
or 72 h. LM attached and survived on the surface and sub-surface 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 sub-surface
structures. Chlorine had a greater effect on the LM on the surface structures compared
to those in the sub-surface structures, possibly because chlorine was not able to access
the sub-surface 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 sub-surface structures of both
tomatoes and spinach, within 30 min, and that even after 72 h, it still remained viable.
