Postharvest Physiology and Storage - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 28

temperature conditioning by combined treatment of heat
shocks and low-temperature storage, fluctuating tempera-
ture during storage (to avoid continuous exposure to risk
temperatures), chemical treatments with calcium or ethy-
lene, and by using fruit coatings (Brown, 1986; Wang and
Adams, 1982; Wang, 1990, 2004; Wang and Qi, 1997).
Furthermore, Gonzalez et al. (2000, 2001) found that a
treatment with methyl jasmonate reduced chilling injury
symptoms in mango and suggested that this compound help
to improve color development of mango fruit of the 'Kent'
cultivar.

Freezing injury
Freezing injury occurs when the fruits are stored at temper-
atures below the freezing point of the fruit, which generally
occurs at a temperature slightly below 0 ◦ C. Since most
tropical and subtropical fruits are sensitive to chilling in-
jury, they are very seldom stored at temperatures below
freezing.
Symptoms vary among products as well as their sensi-
tivity, but in general, for short periods of storage, some
products can tolerate the freezing temperatures. However,
during extended storage under freezing temperature, dam-
age becomes more severe and irreversible.

Figure 2.3. Chilling injury symptoms (pitting, skin
dark spots, and uneven ripening) in purple mombin
during cold storage.

Chilling injury damages can be controlled by proper tem-
perature management during postharvest handling (Hatton
and Cubbedge, 1983; McDonald et al., 1993). Some treat-
ments that have been suggested to reduce product suscep-
tibility to chilling injury include the use of modified at-
mospheres, hypobaric storage, increased relative humidity,

Browning and discoloration
Many fruits are sensible to enzymatic browning of their
tissues. Most of them happen when the fruit is peeled or cut
during processing or as a response to mechanical injuries
from rough handling of the fruit. As the cells are ruptured,
polyphenol oxidase (PPO) and other enzymes are liberated
and come in contact with the native substrates, causing tis-
sue discoloration and darkening (Garcia and Barret, 2010).
Browning can also occur as a result of nonenzymatic re-
actions, such as Maillard reactions, caramelization, or the
oxidation of ascorbic acid, which could occur during heat
processing of the fruits. However, for fresh and fresh-cut
fruits, enzymatic browning is of major quality concern.
Different kinds of phenolic compounds are involved in
the browning reactions, which explain the wide range of
colors and intensity of the tissue darkening, which could be
reddish to brown, blue to gray or black (Garcia and Barret,
2010).
Browning susceptibility varies among fruits and even
among cultivars of the same fruit. It is also affected by
PPO activity in the fruit and the concentration and types of
phenolic compounds participating in the enzymatic brown-
ing reactions. Although in general, discoloration is likely
to increase with PPO activity and the phenolic content, the
relation of these variables with the damage severity is not

Figure 2.4. Chilling injury symptoms (pitting, bright
loss, and failure to ripen) in Tommy Atkins mangoes
during cold storage.