Postharvest Physiology and Storage - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 23

of insects, sunburn, and microbial spoilage, all of which
result in a rapid loss of the fruit commercial value besides
reduced processing yields.
For avocados, oil content and dry matter content increase
as the fruit ripens. However, minimum values required for
every market can largely vary, even for the same cultivar.
For instance, Hass avocados require minimum values of
20.8%, 19.4%, and 26.2% dry matter for fruits commer-
cialized in California, Costa Rica, and Chile, respectively
(Olaeta and Undurraga, 1995; Cerdas et al., 2006; Kader
and Arpaia, 2010a). Oil content is a very desirable attribute
for avocados. Since it is highly correlated to the dry mat-
ter content of the fruit (98%) (Ranney, 1991), it is fre-
quently used as a maturity indicator and a quality evaluation
parameter.
Sweet passion fruit ( Passiflora ligularis, Juss) reaches
its maximum soluble solids content when 25% of the
fruit surface has changed to yellow (used as harvesting in-
dex), though the fruit acidity and color continue to change
(Cerdas and Castro, 2003). Figure 2.1 shows the color evo-
lution of sweet passion fruits as they ripen. In contrast,
the same authors pointed out that wine cultivar blackberry
( Rubus adenotrichus ) showed big changes in the soluble
solids content (6.5-11%) and acidity (4.2-2.7%) as the
fruit ripens and its external color changes from light red to
dark purple.
The respiration rate also changes as the fruit ripens;
furthermore, for some fruits, more than one peak can be
observed. Such is the case of anona ( Annona cherimola ),
which shows two respiration rate peaks, the first one asso-
ciated with fruit softening and the second with flavor and
aroma development, and further texture changes to reach
optimum ripening stage (Lizana, 1994).
Phenolic compounds content changes throughout fruit
development and maturation. Burda et al. (1990) found

significantly lower phenolic content during the early stage
of development of Golden Delicious, Empire, and Rhode
Island Greening apple cultivars, but concentration remains
nearly constant during maturation and storage of the fruits.
They also found a reduction in the tendency to brown
throughout fruit development and ripening which was
closely related to phenolic content of the fruits.
Internal and external color of mango, papaya, banana,
and many other fruits changes, indicating clear signs of
fruit ripening. Color changes generally occur simultane-
ously along with other variations in fruit shape, texture,
and the development of flavor and aromas. For instance,
the external appearance of the skin of cherimoya changes
in color and texture as the fruit loses its trichomes and the
skin texture becomes smoother (Undurraga et al., 1995). It
should also be pointed out that ripening can be affected by
preharvest factors too, such as soil nutrition and cultural
practices, climate conditions, and so forth.

Water loss
Water losses occur as a result of the relative humidity gradi-
ent between the internal atmosphere of the fruit and the sur-
rounding atmosphere. Such losses are partially restrained
by the fruit skin, which functions as a barrier against water
vapor and other gases.
The cuticle, a membrane formed over the epidermal cells
of the fruit skin, is a natural protection of the fruit against
water losses, but it can also help to reduce the effect of
mechanical damage, sunburn, pathogen attack, and other
environmental conditions (Glenn et al., 2005).
The structure, thickness, and composition of the cuti-
cle change as the fruit develops, and even after the fruit is
harvested. The cuticle is likely to respond to environmen-
tal conditions before harvest and under storage conditions
(Glenn et al., 2005); consequently, the barrier permeability

0% 25% 50% 75% overmature

100%

Figure 2.1. Color changes of sweet passion fruit as it ripens.