44 Produce Degradation: Reaction Pathways and their Prevention
the cracks effectively help increase the soluble solids content of the fruit and have
few, if any, deleterious effects.
Cracking also occurs in atemoya (Annona cherimola Mill. × Annona squamosa
L.) during the ripening stage or even postharvest [140]. As with cherries, apples,
grapes, plums, and tomatoes, cracking in atemoya is associated with high soluble
solids content and absorption of water through the fruit skin. Paull [140] observed
that the neutral sugar content of the fruit increased during ripening. The high sugar
concentration in the cells changed the osmotic potential and created a powerful
driving force for water movement into the fruit. The increased cell turgor from water
diffusion into the epidermal and subepidermal cells caused the fruit to swell and
created a mechanical stress that induced cracking.
Aloni et al. [141] noted that cracking in bell peppers was preceded by cuticular
cracks, similar to those found in cherry fruit. The cuticular cracks enlarged into
splits or cracks that penetrated the epidermal, subepidermal, and even the paren-
chyma cells. Cracking in bell peppers occurred under conditions that induced high
cell turgor, such as the relatively low temperatures and high humidity at nighttime
or when the crop was watered heavily after mild drought stress [141].
Storey and Price [31] used cryoscanning electron microscopy to study the epi-
cuticular wax structure of d’Agen plums (Prunus domestica L.). They observed
cuticular fractures along the long axis of the pairs of stomatal guard cells. The
cuticular cracks resulted in a localized loss in moisture and led to the complete
collapse of epidermal cells in the region where the cracks occurred [31].
Litchi fruit is also susceptible to desiccation and subsequent browning [4,142].
Harvested fruits can contain microcracks on their surface, and these microcracks
can extend through the epidermal and subepidermal cell layers. Underhill and
Simons [142] observed that microcracks on the fruit’s surface were not initially
responsible for the desiccation and browning damage of the fruit. In fact, desiccation
initially occurred from high water vapor permeability due to cuticle damage and the
presence of lenticels or a cuticle area that was simply more permeable to moisture
[142]. The microcracks observed on the fruit’s surface developed subsequent to the
initial damage. Nevertheless, the microcracks accelerated the rate of moisture loss.
In addition, the fruit with microcracks had a lower storage life due to fungal infection
at the microcrack sites [142].
Mango fruit (Mangifera indica L.) is protected by a relatively thick cuticle that
can occasionally develop cuticular cracking [17]. The cuticular cracks developed
after anthesis when the cuticle was smooth and continuous, but before fruit set. By
this time, a thick layer of flattened polygonal scales became evident on the epicu-
ticular wax layer. As the fruit continued to develop, cracks traversed the cutin layer
and formed irregular cuticular platelets. Eventually, the mature fruit developed small,
erect scales. The thinnest area of the cuticle corresponded to the grooves formed by
the cracks. Although the cracks did not completely traverse the cuticle, they likely
provided sites for preferential transport of chemicals and potentially made the tissue
more susceptible to chemical damage, blemishes, and desiccation [17].
Cracking can have a large impact on shelf life and degradation of produce.
Cracking can occur when produce swells from moisture supplied either through the
plant vascular tissue or directly through the cuticle surface. Cracking that results