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

FREEDOM PALESTINE FREEDOM PALESTINE FREEDOM PALESTINE
118 Postharvest Diseases of Fruits and Vegetables
When low-temperature storage is used for decay suppression, it is
necessary to take into consideration not only the storage temperature but
also the temperature from which the commodity was removed to cold
storage, and the shelf-life temperature to which it will be transferred.
Maximum storage life prolongation demands the rapid removal of the
Tield heat' from the commodity. Holding the commodity at a high
temperature prior to refrigeration, or delasdng its removal to cold
storage, will permit germination of many of the spores which infest
wounds and will contribute to pathogen establishment in the tissues,
thus shortening the way to decay initiation. In addition, we should
remember that low temperatures during storage are generally not lethal
to the pathogenic fungi and bacteria, but merely retard their
development. When the commodity is transferred to higher temperature
conditions to complete its ripening or for marketing, the pathogen
resumes growth and develops rapidly into decay lesions. Thus, growth of
B. cinerea, the gray mold fungus in strawberries, which is markedly
suppressed during cold storage at 0-2°C, will develop rapidly upon
removal of the fruit to shelf-life conditions. On the other hand, the
exposure of germinating sporangiospores of R. stolonifer to temperatures
close to freezing, causes their death and prevents decay development
during shelf life. It is no wonder, therefore, that the incidence of
Rhizopus rot in peaches stored at O^^C for one week prior to transfer to
ambient temperatures was lower than that in fruits which were held
continuously for a week at room temperature to ripen before marketing
(Pierson, 1966).
Chilling Injury Retardation
In order to store fresh commodities, which are sensitive to chilling, at
temperatures lower than their critical chilling range, their tolerance to
chilling conditions should be enhanced or the appearance of chilling
injury symptoms should be delayed. Various postharvest techniques for
preventing or alleviating chilling injury have been reported during the
recent decades (Wang, 1993).
One approach is to condition fruits at temperatures above the critical
chilling level, to increase their tolerance to chilling during subsequent
low-temperature storage. This method has been found effective in
alleviating chilling injury in several citrus fruits. Preconditioning limes
at 7-20°C for 1 week prior to storage at 1.5°C, or exposure of lemons to 5
or 15°C for 1 week prior to storage at 0-2.2°C, reduced chilling injury
during cold storage (Houck et al., 1990; Spalding and Reeder, 1983).
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