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

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Means for Maintaining Host Resistance 119
Low-temperature conditioning was similarly effective for grapefruits:
preconditioning grapefruits at 10-16°C for 7 days or at IT'^C for 6 days
resulted in reduced chilling injury and decay development during cold
storage of this chilling-sensitive fruit (Chalutz et al., 1985; Hatton and
Cubbedge, 1982). Exposure of papaya fruits to 12.5°C for 4 days
markedly reduced chilling sensitivity at storage temperatures below
7.5°C (Chen and PauU, 1986).
For certain commodities, a double-step, or 'stepwise', temperature
conditioning has been found more effective in reducing chilling injury
symptoms than a single temperature conditioning. The advantage of this
technique was exhibited in mangoes by Thomas and Oke (1983), who
found that preclimacteric mangoes exposed to 20°C for 1 day and then to
15°C for 2 days were more tolerant of storage at 10°C than those treated
with a single temperature conditioning. Marangoni et al. (1990) showed
that tomatoes can also be acclimated to cold storage by gradual cooling:
this included exposure to 12°C for 4 days, to 8°C for 4 days and to 5°C
for 7 days.
Another way to prevent or retard chilling injury is by the application
of intermittent warming. Studies with various horticultural crops have
shown that periodic interruption of cold storage by exposure of fruits to
short periods of warming can reduce chilling injury symptoms and
maintain fruit quality for longer durations (Wang, 1993). The optimum
storage conditions with intermittent warming may vary greatly
according to the cultivar, fruit maturity stage and growing conditions.
For each fruit, however, interruption of chilling exposure with warm
treatments must be performed before chilling injury has developed
beyond a reversible stage. Wang (1993) emphasized the importance of
correct timing and duration for intermittent warming treatments to be
effective; if the critical time at chilling temperature has been exceeded
and chilling injury progressed beyond recovery, the high temperature
would only accelerate the degrading processes and the appearance of
injury symptoms. On the other hand, warming treatments applied too
early or too frequently result in excessively soft tissues, which are
vulnerable to invasion by postharvest pathogens.
Intermittent warming was found to be effective in reducing chilling
injury in various cold-sensitive citrus fruit cultivars. Early studies by
Brooks and McCoUoch (1936) had already shown that removal of
grapefruits from 2°C storage for 1 day after 1 week and again after 2
weeks markedly reduced the development of chilling injury symptoms,
including pitting, scald and watery breakdown. Hatton et al. (1981)
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