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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
152 Postharvest Diseases of Fruits and Vegetables
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Fig. 26. Relationship between pH and the relative concentration of undissociated
hypochlorous acid (HOCl) in a solution of chlorine. (Reproduced from Bartz and
Eckert, 1987 with permission of Marcel Dekker Inc.).
conversion (Robbs et al., 1995). Examining the effect of chlorine solutions
on cells of the bacterium, Erwinia caratovora subsp. carotovora and the
fungus, Geotrichum candidum suspended in water, Robbs et al. (1995)
showed that the chlorine solution toxicity was correlated with free
chlorine concentrations, the pH of the solution and the
oxidation-reduction potential of the solutions. The oxidation-reduction
potential was directly correlated with logic of the chlorine concentration
at each pH. It was also found that cells of JE. carotovora subsp. carotovora
were 50 times more sensitive to chlorine than were conidia of G.
candidum, with populations of 10'^ cells or 10'^ conidia per milliliter,
respectively. Populations of Erwinia were reduced below detectable
levels (> 102 cells ml-i) by approximately 0.5, 0.5 or 0.75 mg l-i of free
chlorine at pH 6.0, 7.0 or 8.0, respectively. With conidia of Geotrichum,
25, 25 and more than 3 mg l-i, respectively, were required to produce
similar levels of efficacy.
In addition, the hypochlorous acid attacks organic matter, and its
concentration in the solution should always be appropriately determined
(Bartz and Eckert, 1987). Although a few ppm active chlorine may be
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