Post harvest diseases fruits and vegetables - Xavier University ...

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Chemical Control 153
sufficient to destroy bacterial cells suspended in clean water within
seconds, 50-500 ppm at pH 7.5-8.5 is frequently recommended for
commercial conditions, necessitating killing bacteria in packinghouse
water containing a considerable amount of soil and organic matter.
Sulfamic acid and other amines have been added to the water to form
N-chloramines, in order to stabilize the concentration of the active
chlorine in the solution. Surfactants are sometimes added to the water to
improve the wetting of vegetable surfaces and to enhance the cleaning
capability of the chlorinated water (Bartz and Kelman, 1984). The use of
chlorine dioxide (CIO2) as a disinfectant has been evaluated for water
containing high levels of organic matter. This compound may be effective
for packinghouse water systems since its efficiency is not significantly
influenced by pH in the presence of organic matter and it does not react
with amines or ammonia, while reacting slowly with organic matter
(Bartz and Eckert, 1987).
Because of its instability in the presence of organic matter, chlorine is
not effective in killing microorganisms embedded within injured tissue
or in natural openings of the host, such as stomata and lenticels. The
effectiveness of chlorine lies, therefore, in its ability to reduce the level of
the inoculum or to eliminate most of the waterborne pathogenic
microorganisms that might inoculate the product during the treatment.
In other words, the main contribution of chlorine solutions to decay
control is the prevention of the buildup of the pathogenic microbial
population in the water used for washing and hydrocooling the harvested
produce. The effectiveness of chlorine on the human pathogen
Escherichia coli, which is responsible for food poisoning outbreaks linked
to the consumption of contaminated vegetables, has recently been
studied. Dipping inoculated Cos lettuce leaves or inoculated broccoli
florets in hypochlorite solutions was found to reduce E. coli counts
significantly more than water alone, but did not eliminate the bacterium
population. The reduction in E, coli cells was dependent on the time of
exposure and the concentration of free chlorine (Behrsing et al., 2000).
Immersing fruits and vegetables in appropriate disinfectants may
actually remove most of the fungal spores from their surfaces. However,
a product that has undergone disinfection may be rapidly reinfested with
pathogenic spores, either directly by the continuous fall of airborne
spores on their surfaces, or by contact with infested equipment in the
packinghouse. An appropriate sanitation system should therefore ensure
both the removal of pathogen sources from every corner and the
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