Microstructure of Produce Degradation 549
cracks in the wax layer on the surface (Figure 18.12g); however, the cracks in the
aged sample were much deeper and fungal hyphae were evident (Figure 18.12h).
A cross section of fresh pear showed angular, thin-walled parenchyma in the
mesocarp and the tissue fractured through cells (Figure 18.13a). The middle lamella
in the aged pear sample was completely destroyed, evidenced by the fracture plane
that occurred around rather than through cells (Figure 18.13b and c). Cells had lost
turgor and intercellular gaps (Figure 18.13b and c) were apparent in the aged sample.
Cell walls in the inner mesocarp were angular and rigid in the fresh pear (Figure
18.13e), whereas in the aged pear the inner mesocarp cell walls were reticulated
and had obviously lost turgor (Figure 18.13f). The cell walls in the aged sample
may have been thicker but it was difficult to determine due to the angle of fracture,
the difficulty in obtaining a clean fracture, and the depth of focus in the SEM.
18.5 CELL COLLAPSE AND DEGRADATION
Grapes, botanically berries, are consumed as fresh fruit, dried fruit, juice, and wine.
There are a multitude of cultivars that make up this vast array of end products. Wine
grapes are typically small and grow in tightly compacted bunches. Some cultivars
are particularly susceptible to bunch rot disease, caused by Botrytis cinerea. The
susceptibility to the disease might be related to the fact that the grape grows in tight
clusters, and thus the microenvironment is ideal for the growth of the fungi [48].
Cell walls also undergo significant changes during development; for example, during
ripening, changes in cell wall composition include significant modification of spe-
cific polysaccharides as well as large changes in protein composition [49,50].
Red seedless grapes, consumed as fresh berries, have a smooth, slightly dim-
pled skin (Figure 18.14a and b). There are no stomata on the berry surface, and
therefore the cuticle plays the major role in vapor diffusion. The aged grape shows
enormous changes in the skin resulting from dehydration followed by the growth
of microorganisms on the surfaces (Figure 18.14c and d). Even in areas having
FIGURE 18.12 (Opposite page)Scanning electron micrographs of ‘Forcelle’ pear skin. (a)
Fresh skin showing the reticulated pattern and lenticels. (b) Aged sample showing the edges
of epidermal cells and a larger reticulated pattern that resulted from cracks around groups of
epidermal cells. The layer of wax had been destroyed and redistributed and as a “bloom”
pattern. (c) close view of the reticulated pattern in the fresh sample that appeared to be fibers
holding the wax platelets together. (d) Aged sample showing part of the bloom and the tops
of the epidermal cells without a wax covering. (e) Lenticel in fresh fruit; fungal hyphae are
growing on the surface and the wax covering is cracked. (f) Lenticel in aged fruit showing
the profuse growth of fungi, the complete destruction of the wax layer, fungal spores, and
exposed epidermal cells. (g) Close view of wax layer on fresh pear. (h) Aged sample, close
view of the disrupted wax in the bloom area; arrow indicates fungal hypha. B, bloom; E,
epidermal cell; L, lenticel. Magnification bars: a, b, 1 mm; c, 10 μm; d, e, 200 μm; f, 100
μm; g, h, 20 μm.