Role of Cuticles in Produce Quality and Preservation 35
2.8.2 BROWNING
A physiological disorder that occurs in Litchi (Litchi chinensis Sonn.) has been
indirectly linked to cuticular function [91]. Litchi is a tropical fruit that commands
a high price in international markets. The red color in the pericarp tissue makes it
a very attractive fruit. After harvest, the pericarp tissue eventually turns brown due
to polyphenol oxidase-mediated oxidation of both phenolic compounds and antho-
cyanins. The browning effect can be delayed by minimizing the moisture loss.
Moisture loss is controlled by storing the fruit at low temperatures and high relative
humidity or by applying a wrap or other moisture barrier [91]. The cuticle of the
fruit itself acts as an important natural moisture barrier and contributes in preventing
desiccation and the browning disorder.
2.8.3 PURPLE SPOT
An important physiological disorder that occurs in loquat fruit (Eriobotrya japonica
Lindl.) is purple spot. The disorder affects approximately 15% of the loquat fruits
in Spain and reduces the market value of the fruit by 40 to 50% [92]. Purple spot
appears as a modest depression on the fruit surface. It is purple in color and has an
irregular shape. Researchers have suggested that local deficiencies in calcium may
lead to the development of purple spot [93]. However, Gariglio et al. [92] found no
correlation between calcium concentrations in loquat fruit and the incidence of
purple spot. They also investigated the water permeability of the loquat fruit cuticle
to determine whether desiccation could play a role in the development of the disorder
as it does in the browning disorder of litchi fruit. They used isolated fruit cuticle,
but found no sign of damage or disruption of the cuticle in the damaged area
compared to healthy areas. They also saw no change in the water permeability of
the cuticle and concluded that other factors were responsible for the development
of purple spot in loquat fruit.
2.8.4 SCALD
Superficial scald is a physiological disorder that occurs postharvest in apples and
pears [94]. Superficial scald appears as a browning of the fruit skin and can affect
the entire fruit surface. The accumulation of α-farnesene and perhaps other volatile
compounds has been implicated in the development of scald. The cuticle can sorb
lipophilic, volatile compounds such as α-farnesene and consequently can promote
the development of scald [28]. Fallik et al. [95] measured the amounts of α-farnesene
and other volatile compounds in apple fruit with and without the cuticle intact and
noted that the cuticle provides a poor barrier to volatile compounds. However, they
did not investigate the sorptive properties of the cuticle. Ju and Bramlage [28] further
noted that various phenolic compounds present in fruit cuticle might decrease oxi-
dation of α-farnesene, which would counter the development of scald [28]. Inter-
estingly, postharvest dips of apples and pears in plant oil emulsions or coating with
natural and synthetic commercial wax products have been shown to affect the
physical and chemical properties of the cuticle and reduce the development of scald