Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

HEAT TREATMENT FOR ENHANCING POSTHARVEST QUALITY 249
1.4 80
1.2
1
70
60
0.8
50
Control
Control
40
0.6
50°C, 2 h
50°C, 2 h
30
0.4
20
0.2
10
0
0
0 2 4 6
0 2 4 6
(a) Days in 15°C storage
(b) Days in 15°C storage
Fig. 11.3 Chlorophyllase (a) and chlorophyll degrading peroxide, and heated florets were held in hot air at 50 ◦ C
for 2 h before storage. (Adapted from Funamoto et al., 2002, 2003.)
Units/mg protein
Units/mg protein
after the heat treatments. However, the same treatments applied to Brussels sprouts were
not effective in delaying yellowing.
Other processes that involve ethylene in harvested vegetables, such as geotropic bending
of asparagus (Paull and Chen, 1999) and extension growth of green onions (Hong et al.,
2000; Cantwell et al., 2001), were also controlled by hot water treatments before storage.
Hot water dips controlled sprout and root growth in garlic cloves (Cantwell et al., 2003).
Sprouting and spoilage of potatoes were also inhibited by a hot water dip (Ranganna et al.,
1998). The best treatments to inhibit these physiological processes were hot water dips from
2 to 4 min in the temperature range of 50–55 ◦ C.
11.4 Effects on chilling injury
The storage temperatures of subtropical fruits and vegetables are arrived at by a compromise
between temperatures, which are low enough to inhibit ripening processes, but cause chilling
injury, and those which are high enough to avoid chilling injury, but do not prevent the
continuation of ripening. Inducing resistance in a fruit or vegetable to chilling injury will
allow it to be stored at a lower temperature. This in turn may allow transport in ships rather
than the more costly airfreight. In addition, a preshipping heat treatment can allow for lowtemperature
disinfestations of commodities, such as citrus, by improving the resistance of
fruit to the chilling injury generally incurred during this treatment. Table 11.1 tabulates
some of the commodities that have been tested for high-temperature induction of resistance
to low-temperature injury. The table is partial because this is a dynamic field of research
and new studies are appearing regularly.
What is apparent from the table is that a time–temperature regime can be found for any
commodity that will reduce chilling injury. The successful treatment is arrived at empirically,
by trial and error, and what works on one cultivar may not be as successful on another. For
example, Israeli citrus fruit respond well to a hot water dip of 3 min at 53 ◦ C (Rodov et al.,
1995). A number of citrus varieties including grapefruit, lemon, oroblanco, and kumquat
all had reduced chilling injury after these two treatments and low-temperature storage.
However, “Tarocco” blood oranges grown in Italy will be heat damaged by a hot water
dip of 3 min at 53 ◦ C, but respond favorably to 3 min at 50 ◦ C by reduced chilling injury
(Schirra et al., 1997). Another example of differences among cultivars involves hot air
treatment. A hot air prestorage treatment of 2 days at 37 ◦ C caused off-flavors to develop
in “Tarocco” blood oranges (Schirra et al., 2002), but was helpful in controlling chilling