20 Produce Degradation: Reaction Pathways and their Prevention
2.1 INTRODUCTION
The best ways to extend the shelf life of produce postharvest include reducing
desiccation, lowering the rate of senescence and maturation, and reducing the rate
of microbial infection [1]. The cuticle or the cuticular membrane plays an integral
part in extending the shelf life of many different kinds of produce. The cuticle forms
a continuous extracellular membrane over the epidermal cells of most aerial plant
parts, including leaves and fruits [2–5]. The primary function of the cuticle is to
minimize water loss [6] by mediating the wettability of the tissue surface and
moisture vapor permeability [7]. Another important function of the cuticle is to
prevent the loss of plant solutes through leaching [8,9]. In recent years, the cuticle
has been found to possess other functions as well. It provides the first line of defense
against pathogen invasion [10], acts as a shield against mechanical impact, facilitates
the efficient exchange of gases, provides some protection from exposure to pesticide
and fertilizer chemicals, and reduces damage from solar irradiation [11] and herbi-
vores [6,7,12]. Some have viewed the cuticle as inert, nondynamic plant tissue
because it is extracellular. In reality, the cuticle may constantly change during the
lifespan of a particular fruit or vegetable.
This review chapter covers the current knowledge of plant cuticle properties and
functions as well as how these might relate to the quality and preservation of produce.
It is not our intent to provide a comprehensive survey of all commercial produce.
For instance, produce from roots (e.g., carrots) or tubers (e.g., potato) are not
discussed here because their protective skins generally have different anatomical
and structural features. Rather, we primarily focus on a few representative examples
that illustrate the cuticle’s important role on produce quality and preservation.
2.2 GENERAL STRUCTURE AND COMPOSITION
OF PLANT CUTICLESVarious microscopy techniques have been developed that provide valuable informa-
tion on the structure and composition of the cuticle. These techniques include light
microscopy used in conjunction with different staining methods, scanning electron
microscopy (SEM), and transmission electron microscopy (TEM). More recently,
confocal laser scanning microscopy techniques have been used to investigate the
epicuticular wax layer [13,14] as well as to localize phenolic and flavonoid com-
pounds in plant cuticles.
The cuticle is not simply a homogenous membrane that covers the epidermal
cell layer in plants [15,16], but rather it contains a layered structure [2]. In addition,
the cuticle structure and composition varies among plants and among different organs
of the same plant and changes as the plant tissue grows and matures [4,15]. In one
study, Bird and Gray [15] described the changes in the cuticle of developing leaf
tissue. The young, juvenile tissue is covered with a highly water-repellent wax layer
they referred to as the procuticle. As the leaf develops, the cuticle thickens and adds
to the wax layer. The layers of cutin and cell wall polysaccharides then form to
produce a lamellar structure. This lamellar structure is referred to as the cuticle