36 Produce Degradation: Reaction Pathways and their Prevention
[28]. The data indicate that the cuticle plays an indirect role in the development of
superficial scald and that modifying the properties of the cuticle with coatings can
alter scald development [28].
The cuticle has been directly or indirectly implicated in the development of
various other physiological disorders. Rindstaining in oranges (Citrus sinensis L.)
was more severe in regions where the epicuticular wax layer was disrupted [96]. In
addition, brown core in pear (Pyrus bretschneideri) was closely correlated with
changes in the composition of epicuticular waxes [97]. Moreover, chilling injury in
grapefruit has been linked to the composition and amount of epicuticular wax in the
fruit cuticle [98]. More research is needed to clarify the role of the cuticle in the
development of each of these disorders.
2.8.5 CUTICULAR CRACKING
In their extensive review of fruit cracking, Opara et al. [99] described cracking as
a general term for certain physical disorders of fruits. These disorders appear as
fissures or fractures that penetrate the cuticle, the skin (cuticle, epidermal and
subepidermal cell layers), or the flesh (skin and underlying tissue) of produce. Flesh
cracking is one of the most widespread physical defects found in the production of
fruit [99]. Such cracks are very visible and are easily noticed by consumers. The
properties of the cuticle may be important in the initial development of flesh cracks,
especially if moisture absorption through the cuticle surface initiates the cracks. The
economic importance of cuticular cracking is much more difficult to assess compared
to that of flesh cracks. Cuticular cracks are difficult to see with the unaided eye, and
consequently the prevalence of the problem remains unknown. However, the prop-
erties of the cuticle are thought to be particularly important in cuticular cracking.
The following section provides a detailed discussion of cuticular cracking in various
types of produce. Particular emphasis is given to sweet cherries as an illustration of
a commodity influenced considerably by cuticular cracking.
2.8.5.1 Cherry
Cherry fruit (Prunus avium L. cv. Bing) is covered by a thin (1 μm), smooth cuticle
[100]. Cross-sectional views of the fruit show that the epidermal cell layer consists
of relatively small (ca. 40 μm), rectangular cells with thick cell walls (Figure 2.2
and Figure 2.3). In addition, there are one to three layers of subepidermal cells that
are oblong shaped and intermediate in size. The parenchyma cells that make up the
bulk of the fruit’s flesh are relatively large (ca.150 μm) and round with very thin
cell walls. Meanwhile, the cuticle has a smooth surface and is nearly devoid of
epicuticular wax formations or bloom. The only exception to the smooth surface is
a shallow reticulate pattern of epicuticular wax that is visible near the stylar scar
end of the fruit (Figure 2.4). These reticulate epicuticular wax formations can also
be seen in cuticles enzymatically isolated from the fruit (Figure 2.5). The smooth,
planar surface of the epidermal cell layer combined with the lack of bloom on the
cuticle surface make the fruit glossy and very attractive (Figure 2.6).