Role of Cuticles in Produce Quality and Preservation 25
the cuticle continues to grow, albeit at a reduced rate [26]. In addition, postharvest
apples show a considerable increase in the amount of epicuticular wax compared to
preharvest apples.
Ju and Bramlage [27] further documented changes in wax content of apple fruit
cuticle during fruit ripening and storage. They observed that all wax components
increased during fruit ripening, with free fatty acids and alcohols contributing the
most to the increase. These waxy products formed a greasy film postclimacteric in
apple as well as pear fruit [28]. These changes appear to be triggered by the
climacteric rise in respiration. Experiments with Ethephon and AVG have provided
evidence supporting this claim. Ethephon treatments have been shown to accelerate
the climacteric rise in respiration and accelerate the changes in the wax components
of the cuticle. On the other hand, AVG treatments have been shown to suppress the
climacteric rise in respiration and suppress the changes in cuticular waxes [28].
2.3.2 VARIABILITY IN CUTICLE STRUCTURE AND COMPOSITION
The expression of different genes within the plant genome can cause some variability
in the cuticle structure and composition on a specific plant. For instance, the cuticle
on leaves of apple trees is very different from the cuticle on the fruit’s surface. The
mass of the fruit cuticle may be as much as 2,000 μg × cm–2, whereas the mass of
leaf cuticle may range from 450 to 800 μg × cm–2 [2]. Natural variation in the cuticle
structure can also occur in different regions of the produce itself. Farag [29] observed
that in ripening cranberry fruit, the wax accumulates more in the calyx region than
in other areas. Variations in the cuticle structure also occur among plants with very
similar genomes. For example, Veraverbeke et al. [30] found differences in the
thickness of the epicuticular wax layer among three different apple cultivars.
Variations in environmental conditions can also affect cuticle structure and
development, especially the epicuticular wax layer. In some produce, crystalline wax
structures are extruded to the external surface of the cuticle, giving fruits their
characteristic waxy bloom [31]. For instance, the presence or absence of bloom on
various regions of the apple’s cuticle has been attributed to variations in the amount
of incident radiation exposure. The epicuticular wax layer can partially protect the
plant tissue from visible and infrared radiation by reflecting and/or refracting incident
radiation [32,33]. Consequently, the shaded regions seldom have as much epicutic-
ular wax as regions exposed to sunlight [32,33]. In addition, differences in the
amount of bloom could also be influenced by variations in other microclimatic
conditions [31,32].
Veraverbeke et al. [30] studied the effect of controlled atmosphere storage on
cuticle development. They stored apples in controlled atmosphere storage for dif-
ferent time periods before removing them and determining the wax composition.
They found that apples held in controlled atmosphere storage for longer periods
exhibited a greater change in wax composition once they were brought out of storage
and acclimated at room temperature. The alkane and ester fractions showed the
largest amount of change. Using confocal laser scanning microscopy, Ververbeke et
al. [30] also studied the epicuticular layer of the apple cuticle. They noted that apples
stored in a controlled atmosphere environment developed cracks in the cuticle