Temperature Effects on Produce Degradation 629
a result of this study and a number of others, it was concluded that fatty acid
composition in membrane lipids may not be the only factor that determines phase
transition and fluidity of the membrane. Other membrane components, such as sterols
and cholesterol or the lipid-protein complex, may also be involved in regulating
membrane fluidity.
20.4.1.4 Treatments to Alleviate Chilling Injury
The most obvious way to prevent chilling injury is to store susceptible commodities
above the temperature at which the injury will occur. In commercial practice, how-
ever, a wide range of commodities is often stored together and at a compromise
temperature chosen to minimize chilling injury of susceptible products while extend-
ing the shelf life of nonsusceptible products as much as possible.
A number of studies have been conducted to identify treatments to alleviate
chilling injury. Some treatments have been applied directly to the commodity, while
others involve manipulation of the product’s environment.^28 Treatments that have
shown promise include ensuring proper humidity levels during cool storage, condi-
tioning the produce at near-chilling temperatures before chilling, intermittent warm-
ing treatments during chilling, increased CO 2 in the atmosphere during chilling,
pretreatment with calcium or ethylene, and holding under hypobaric conditions
during chilling.
Chilling injury may be reduced if the storage humidity is either high or low,
depending on the commodity.^30 The mechanism of high humidity prevention of
chilling injury may be in preventing drying out of injured tissue. Low humidity may
prevent injury by enhancing the loss of volatile toxins from the tissue.
Reduction of the incidence of chilling injury has been observed in some produce
when it is held at room temperature for a period before being placed in cold storage.^32
Chilling injury was reduced in sweet pepper fruits stored 5 or 10 d at 10°C prior to
subsequent storage at 0°C.^33 A 7-d exposure of grapefruit to 10 or 15°C prevented
or significantly reduced chilling injury during storage at 0 or 1°C. Produce showing
reduced chilling injury after delayed cold storage were the ones that were ripening
at harvest or beginning to ripen just after harvest.^32 Thus, the reduction of chilling
injury by delaying storage seems to be related to alteration of the stage of ripening
when the fruit enters storage.
The use of high temperatures (38°C or higher) has been shown to be an effective
way to increase resistance to low temperatures in some products.^3 In practice, a
prestorage high-temperature treatment is often used for insect disinfestation or for
fungal control. In some products, however, this elevated temperature also can slow
the progression of ripening and, therefore, assist in maintaining quality. A high-
temperature prestorage treatment was found to inhibit chilling injury in avocado,
citrus fruits, mango, papaya, persimmon, and some apples.
The mechanism by which heat treatment protects against chilling injury is not
known. Exposure of some plant tissues to temperature stress for several hours or
more has been shown to induce a heat-shock response characterized by reduced total
protein synthesis and the production of specialized heat shock proteins (HSP).^13
These HSPs confer thermotolerance so that subsequent exposure to normally lethal