Postharvest Physiology and Storage - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 22

sprouting of potatoes, excessive softening of fruits, reduc-
tion of storage life, and synthesis of bitter compounds in
carrots. It can also favor some physiological disorders and
increased sensitivity to microbial spoilage.
Both the production of ethylene and the sensitivity to
external sources of this gas vary among fruits and their
stage of maturity. Therefore, it is important to consider
that ethylene can be produced by fruit tissues during ripen-
ing, but also it can be produced from diseased plant tis-
sues and combustion engines, and thus care should be
taken during storage to control its presence and the com-
patibility of the fruits according to their ability to pro-
duce and respond to ethylene. Ethylene production rates
of selected tropical and subtropical fruits are shown in
Table 2.4.
Low concentrations of ethylene can promote its auto-
catalysis (Yang and Hoffman, 1984; Abeles et al., 1992) in
mature fruits and senescent tissues, increasing its produc-
tion. However, the response of this process could be delayed
for weeks for some products. Peacock (1972) pointed out
that autocatalytic response is due to the destruction of en-
dogenous ripening inhibitors in the presence of ethylene,
which at the same time triggers its production. In contrast,
ethylene presence can also inhibit its own production in
some products (Yang and Hoffman, 1984; Woeste et al.,
1999; Argueso et al., 2007).
Ethylene production is also promoted by extrinsic factors
such as mechanical damages (cuts, bruising, scratches), de-
cay, insect damages, and climate conditions (temperature,
relative humidity), as a response of the tissues to different
type of stress. Hoffman and Yang (1982) found out that
even though ethylene production is low in immature mel-
ons ( Cucumis melo ), it increases rapidly as a response to
mechanical damage.
Mattoo and Bruce (1991) also found an increase in ethy-
lene production when citric fruits flavedo is physically in-
jured. Abeles (1973) pointed out that insect damages can
be associated with the action of some cellulytic and prote-
olytic enzymes to trigger ethylene production and ripening
of figs.

riety of volatile components, result in fruit flavor changes
during ripening, making the fruit more appealing and
tasteful.
Fruit softening also occurs during ripening as a result of
starch degradation, changes in the fruit cell walls, and loss
of turgor pressure due to water loss during storage.
Maturity stage at which fruits are harvested is one of
the most important factors that influences their quality and
storage life. The rate and nature of the ripening process
varies among fruit species, cultivars, production sites, and
handling and storage conditions after harvest.
Ripening of climacteric fruits is triggered by natural
changes in hormone composition. The ripening process
is characterized by a rapid increase of the fruit respira-
tion and ethylene production, known as climacteric peak,
which coincides with an augmentation in the sugar and
carotenoids contents, a decrease in the fruit acidity, total
phenols content, firmness and starch content, and changes
in the activity of several enzymes (Kays, 1997; Tejacal
et al., 2002). In contrast, ripening of nonclimacteric fruits is
gradual.
Immature fruits can show one or several of the following
problems: larger sensitivity to wilting, weight loss, transpi-
ration, chilling injury, and mechanical damages occurred
by impact, compression or friction stresses, and uneven
or incomplete ripening with reduced quality or increased
sensitivity to physiological disorders (Saltveit and Morris,
1990; Pereira et al., 2003; Cerdas et al., 2006). It is likely
that for fruits harvested immature, cuticle formation is in-
complete, which results in a poor protection of the fruit
against water loss.
Increased susceptibility to chilling injury has been
observed for immature purple mombin fruit ( Spondias
purpurea ), a Latin America native fruit of the Anacar-
diaceae family, stored at temperatures below 14.5 ◦ C, in
contrast with mature fruit which is less sensitive to this
damage. Color development of the skin, firmness, soluble
solids contents, and acidity of immature guavas (Azzolini
et al., 2004) are affected by the stage of maturity of the
fruits when harvested.
For avocados of the Hass cultivar, Cerdas et al. (2006)
reported that seed and its integument (thin covering of
the seed) and some parts of the fruit skin keep strongly
adhered to the fruit flesh when the fruit is immature,
and also the fruit flesh does not develop its characteristic
flavor.
Conversely, overripe fruits become soft and more diffi-
cult to handle and process, as they are more sensitive to
mechanical damage. They lose flavor and color, and off
odor is formed and the fruit rapidly deteriorates because

Fruit ripening
Metabolic activity of the fruits leads to changes in color,
flavor (taste and aroma), texture, starch, and phenolic and
other compound contents. The degradation of chlorophyll
and the production of anthocyanins and carotenoids result
in color changes in the fruit, though some of these pig-
ments can be produced in the green tissues, and they are
“hiding” by the chlorophyll until its degradation during
ripening. Sugar and organic acids, together with a large va-