Production Practices and Quality Assessment of Food Crops. Vol. 1
Production Practices and Quality Assessment of Food Crops. Vol. 1
Production Practices and Quality Assessment of Food Crops. Vol. 1
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<strong>of</strong> more than 13 hours <strong>of</strong> night temperature below 15.6 °C during the week preceding<br />
harvest would cause irreversible damage resulting in visible symptoms during<br />
marketing. This treatment may, however, cause undesirable s<strong>of</strong>tening <strong>and</strong> increase<br />
decay <strong>and</strong> may cause condensation to form on the product especially in storage<br />
(Skog, 1998). Preconditioning can also be used. It is the stepwise cooling <strong>of</strong> the<br />
commodity <strong>and</strong> can allow the vegetable to adapt to the cooler temperature <strong>and</strong><br />
minimize chilling injury development in storage.<br />
Controlled or modified atmospheres (generally O 2 < 5%, CO 2 > 2%) can slow<br />
plant metabolism <strong>and</strong> slow chilling injury development in certain crops. Controlled<br />
atmospheres can also allow longer storage <strong>of</strong> chilling sensitive crops when stored<br />
above their critical temperature (Skog, 1998). Modifying the atmosphere surrounding<br />
certain fruits subject to a number <strong>of</strong> low temperature disorders has been reported<br />
in some instances to alleviate or delay the symptoms usually associated with chilling<br />
injury (Lyons <strong>and</strong> Breidenback, 1987). Reduced O 2 <strong>and</strong> elevated CO 2 can overcome<br />
the impact <strong>of</strong> low temperature injury on the ripening process (Wade, 1979; Ilker<br />
<strong>and</strong> Morris, 1975). Controlled atmospheres may in some cases further stress crops<br />
<strong>and</strong> increase chilling injury susceptibility for crops such as cucumbers, tomatoes <strong>and</strong><br />
asparagus (Skog, 1998). Maintaining a high RH around the commodity during<br />
storage, as occurs with film wraps <strong>and</strong> modified atmosphere storage, reduces the<br />
severity <strong>of</strong> chilling injury symptoms by minimizing desiccation.<br />
Proper pre-harvest nutrition can minimize chilling susceptibility. Calcium treatments<br />
may stabilize cellular membranes <strong>and</strong> reduce chilling injury in certain<br />
commodities. Ilker <strong>and</strong> Morris (1975) found that treatment with solutions <strong>of</strong> calcium<br />
<strong>and</strong> potassium salts could afford some protection against chilling injury in okra. The<br />
severity <strong>of</strong> chilling injury in squash (Cucurbita moschata) fruits, stored at 4 °C<br />
was reduced by dipping in 1% CaCl 2 or 10 mM sodium benzoate at 20 °C for 30<br />
minutes (Lee <strong>and</strong> Yang, 1999). Fruits treated with sodium benzoate showed a low<br />
incidence <strong>of</strong> chilling injury (< 10 °C) following 30 days <strong>of</strong> storage at 4 °C.<br />
Reports examining possible approaches to alleviating chilling injury conclude that<br />
the most likely solution occurs through genetic modification (Graham <strong>and</strong> Patterson,<br />
1982; Couey, 1982; Bramlage 1982). A better underst<strong>and</strong>ing <strong>of</strong> the primary causes<br />
<strong>of</strong> chilling injury will provide information for the development <strong>of</strong> rapid methods<br />
for screening potential germ-plasm <strong>and</strong> possibly control <strong>of</strong> this disorder. The debate<br />
as to whether there is a single primary response <strong>and</strong> whether the membrane plays<br />
a central role as the primary temperature sensor remains unresolved.<br />
3.2. Freezing injury<br />
Effect <strong>of</strong> Preharvest Factors 11<br />
Commodities may be frozen in the field before or during harvest, in transit <strong>and</strong><br />
storage. Vegetables vary in their susceptibility to freezing injury. Some may be<br />
able to go through freezing <strong>and</strong> thawing several times with little or no apparent<br />
damage, while others are damaged by slight freezing. The relative susceptibility<br />
<strong>of</strong> fresh vegetables to freezing injury is shown in Table 4. The inherent susceptibility<br />
<strong>of</strong> tissues to freezing stress may be partially responsible for this variation in<br />
sensitivity. Ice nucleating bacteria may also play an important role. Whether or<br />
not ice formation in the tissues is accompanied by permanent injury <strong>and</strong> death