Role of Cuticles in Produce Quality and Preservation 37
The primary cause of flesh cracking in sweet cherries is due to rainfall near
harvest time [101]. Borve [102] covered cherry trees with different kinds of protec-
tive coverings and were able to save about 89% of the fruit during the season. In
contrast, trees with no protective covering suffered a 54% crop loss. Fruit cracking
that occurs in the field during rainfall typically develops as a crescent-shaped crack
near the fruit pedicel where water may accumulate. Cracks may also occur in the
region of the stylar scar where the water tends to drain from other areas of the fruit
and accumulate into a drop of water [101,103]. In one study, Yamaguchi [104]
reported that fruit weight, flesh firmness, and skin cell size largely determined the
cracking susceptibility of cherry fruit. Lane et al. [105] looked at various parameters
that might explain the susceptibility and resistance of different cherry varieties to
cracking. They studied mineral composition of the fruit, skin elasticity, cuticle
thickness, and geometry of the mesocarp and epidermal cells. However, none of
those parameters could account for the differences observed in cracking suscepti-
bility among susceptible and resistant varieties.
Researchers disagree on whether stomates are an important penetration site for
water uptake in cherry fruit. Peschel et al. [106] studied the distribution of stomates
in the cherry fruit epidermal layer to determine whether stomates were important in
water penetration through the cherry skin. They found a greater density of stomates
near the stylar scar, where cracking often occurs, and a lower amount near the stem,
another common site for cracks. They observed that the stomates did not function
in mature, ripe fruit and that the critical surface tension necessary for water to enter
the stomates was not achieved. Consequently, Peschel et al. [106] concluded that
the stomates were unlikely to be important pathways of water absorption. In another
study, Knoche et al. [107] examined the permeation rate of water through the cherry
fruit surface using pericarp tissue mounted in a diffusion cell. They found a positive
relationship between water conductance and stomatal density, although the stomates
appeared to be only a minor pathway of water penetration [107].
Beyer et al. [103,108] studied preferential water absorption in various regions
of cherry fruit. They found that the pedicel cavity and surrounding regions were
important areas of water absorption. Knoche and Peschel [109] studied the transport
of water through the surface of sweet cherry fruit by using hydrostatic pressure to
infiltrate the fruit. They found the mature fruit had a greater water uptake, most of
it through the pedicel/fruit juncture. Water or solutes have also been shown to
penetrate the fruit surface through the stylar scar region [100,107,110]. As the fruit
develops and increases in size, the stylar scar region also increases in size. Conse-
quently, this region could possibly become an increasingly important site of water
penetration.
Knoche et al. [107] reported that fresh cherry fruit and fruit stored for 42 days
showed no difference in skin permeance. The results suggest that the cuticle under-
went little or no change during storage. However, conductance increased from the
cheek to the ventral suture and the stylar end. The importance of cuticular waxes in
water permeance was determined by treating the cuticle surface with solvents to
remove the waxes. When their surfaces were treated with cellulose acetate and