Temperature Effects on Produce Degradation 641
20.5.6 CITRUS FRUITS
Many species of citrus fruit are susceptible to chilling injury. Common symptoms
include surface pitting (Figure 20.11), browning or darkening of the membranes
between the segments, discoloration of the white spongy tissue and, after storage
below 2°C, a water-soaked appearance of the flesh.^7 The development and severity
of chilling injury in citrus is influenced by both preharvest and postharvest factors.^64
With oranges, the location of production affects the development of chilling injury.
Fruit grown in California and Arizona may develop chilling injury when held at
temperatures below about 3 to 5°C, while oranges produced in Florida or Texas
rarely show chilling injury. Other preharvest factors that affect the development of
chilling injury in citrus fruits include cultivar, weather conditions, and even location
of fruit on the tree (sun-exposed fruit is more susceptible to chilling injury).
Postharvest, the best means of preventing chilling injury is by storing fruit at
nonchilling temperatures.^64 Development of chilling injury symptoms also can be
reduced through temperature conditioning before storage, use of high-CO 2 atmo-
spheres (e.g., in controlled atmosphere storage or through the use of wax coatings
or plastic film wraps), intermittent warming, and use of benzimidazole fungicides
(e.g., thiabendazole and benomyl).
Decay associated with Pencillium infection may be reduced in oranges by expos-
ing the fruit to temperatures of 30°C and 90 to 100% RH for several days after
harvest.^65 Pencillium digitatum infection was inhibited by sealing lemons, pomelos,
and grapefruit in plastic bags then exposing them to 34 to 36°C for 3 d. This treatment
resulted in lignification and an increase in antifungal materials in the peels.
Insect disinfestation of citrus fruit is usually accomplished by holding the fruit
at 0 to 2.2°C for 10 to 16 d before raising the temperature to the normal storage
temperature of 6 to 11°C, depending on the cultivar.^66 Since citrus is susceptible to
chilling injury, fruits are usually held at 20°C for 3 to 5 d before being placed in
the low temperature. This holding period decreases susceptibility of the fruit to
chilling injury during the subsequent low-temperature disinfestation treatment.
An alternative method of disinfesting citrus fruit is a high-temperature, forced-
air treatment.^66 In this treatment, fruits are heated to a temperature of 44°C over a
period of 90 min. They are held at this temperature for an additional 100 min before
being cooled to their storage temperature.
20.5.7 TOMATOES
Tomatoes are usually harvested when they are mature green or partly colored. The
objective in storage after harvest is to control the rate of ripening. Temperatures
below 13°C in the field or in storage may result in damage caused by chilling injury.^67
Chilling injury symptoms include alterations in the rate of color change and the
development of such effects as uneven coloring, pitting, breakdown, and poor flavor
development (Figure 20.12 and Figure 20.13). The extent of injury depends on the
storage temperature, the time the tomatoes are exposed to the temperature, and the
stage of fruit ripeness. Green and breaker stage fruits are considered more susceptible
to chilling injury than are ripe fruits.^36