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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
40 Postharvest Diseases of Fruits and Vegetables
The interrelations among the environmental temperature, the
pathogen and the host can be depicted as a triangle displaying the effect
of the temperature on each of the others, which have their own mutual
interrelations:
TEMPERATURE
^ HOST
PATHOGEN
In fact, a significant proportion of the decay that occurs in the
markets, particularly that of tropical fruits, results from overexposure to
damaging temperatures. For some tropical fruits and vegetables, storage
below 10°C is sufficient to cause chilling injuries, even when external
physiological symptoms are not visible.
The use of low temperatures to depress decay by maintaining host
resistance will be described in a separate chapter (See: Means for
Maintaining Host Resistance - Cold Storage).
2. RELATIVE HUMIDITY AND MOISTURE
The high relative humidity (RH) required for the protection of fruits
and vegetables from dehydration and weight loss might stimulate
pathogen development during storage. The danger of decay is enhanced
by the condensation of mist over the fresh fruit or vegetable surface.
Similarly, wrapping the fruit or vegetables in sealed plastic film with low
permeability to water vapor often causes enhanced decay when these
films are not punctured and ventilated. Rodov et al. (1995c) found that
the RH within an airtight polymeric wrap can be reduced by adding a
hygroscopic substance such as sodium chloride. This reduction results in
a reduced decay of peppers wrapped in a polyethylene film and stored at
8°C. Without the insertion of the hygroscopic substance, the relative
humidity within the wrapping might approach saturation, with
condensed water drops on the fruit and on the wrapping inner surface.
Leafy vegetables and, especially, leafy herbs, characterized by rapid
dehydration following harvest, store better under high RH and
subsequently decay less because of the reduced accumulation of dead
tissues, which may provide nutrients for decay organisms (Yoder and
Whalen, 1975). Packing such crops in polyethylene-lined crates has the
advantage of preventing dehydration and preserving turgidity. The main
limitation to the use of polymeric film packaging is the water condensation
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