Production Practices and Quality Assessment of Food Crops. Vol. 1

06. Failure of fruits to ripen in the expected pattern following removal to ripening
conditions.
07. Accelerated rate of senescence, but with an otherwise normal appearance.
08. Increased susceptibility to decay due to leakage of plant metabolites that
encourage growth of microorganisms.
09. A shortened storage shelf life due to one or more of the above responses.
10. Composition changes – especially in relation to flavour and taste.
11. Loss of growth (sprouting capacity – important with stored propagules).
These symptoms are not unique to chilling injury and many can also be induced
by water stress and anoxia. The symptoms may not be evident while the commodity
is held at the chilling temperature and develop rapidly when removed from
cool storage. In most studies directed toward determining the extent of chilling injury,
a treatment of varying times and temperature is applied and then the test material
is placed at 20–25 °C for 3 days for observation.
The factors that influence the relative susceptibility of vegetables to chilling injury
are, genetic diversity, stage of physiological development and the conditions under
which the commodities are grown. Cultivars within a sensitive species can differ
in symptom expression. King and Ludford (1983) showed that differences in chilling
sensitivity among 5 tomato cultivars as measured by electrolyte leakage could be
discerned prior to the development of visible symptoms. Tomato fruit are quite
susceptible to chilling in their mature green stage (Autio and Bramlage, 1986).
Chilling sensitivity decline, as ripening progress and then increase again during
the late stages of ripening. Fully mature honeydew melons were less susceptible
to chilling injury than less mature melons (Lipton, 1978). Mature green fruits of bell
peppers (Capsicum sp) showed surface pitting after storage at 1 °C for 3 days,
while full colour of fruits showed no chilling injury after 2 weeks at 1 °C (Lin et
al., 1993). The conditions under which the commodities are grown may influence
the extent and development of chilling injury (Kader, Lyons and Morris, 1974). Some
winter-grown tomatoes were more susceptible to chilling injury than summer grown
fruit of the same cultivar (Abdel-Madsoud et al., 1974). Fully ripe, firm fruit can
be held at 0–2.5 °C for short periods if they are to be consumed immediately upon
removal from refrigeration. Some of the important vegetables susceptible to chilling
injury and the potential symptoms are listed in Table 3.
3.1.3. Alleviation of chilling injury
Effect of Preharvest Factors 9
Chilling injury can be avoided by limiting growing, handling and storage of sensitive
crops above the critical threshold temperatures. Growing cultivars that are less
sensitive or tolerant of chilling injury is probably the only way of effectively reducing
chilling injury in the field. Several other temperature treatments have been tried with
various degrees of success to control mostly chilling injury in storage. These will
be discussed briefly below.
High temperature conditioning treatments have been reported to enhance the
chilling tolerance of a number of chilling sensitive tissues (McCollum and
McDonald, 1993). Cucumber fruits immersed in 42 °C water for 30, 45 or 60 minutes