Microstructure of Produce Degradation 547
and cellulose microfibrills, resulting from the depolymerization of the cell wall,
became more apparent [28]. Thus, long-term storage can result in a number of
microstructural changes in tissues.
The microstructure of pears has a tremendous influence on their storability, and
different treatments to increase shelf life influence the microstructure. Calcium
sprays and early harvest dates reduced disorders such as brown core, cork spot, and
superficial scald on pears [44]. Irradiation and calcium treatment was found to be
effective in increasing shelf life; irradiation reduced the microbial load but softened
the skin and calcium reduced the amount of softening caused by irradiation treat-
ments [45]. Neither treatment changed the microstructure of the pear skin.
De Belie et al. [46] studied the influences of cell turgor and fruit ripening on
pear tissue and characteristics of the cells. Intercellular fractures occurred in firm
tissues, intracellular fractures occurred in soft tissues, and both types of fractures
occurred at intermediate firmnesses. Pears were incubated in solutions of differing
water potential, and for firm pears a clear influence of the water potential of the
incubation solution was found. There was no influence of water potential in soft
pears, however. In firm pears, incubation in hypotonic solutions resulted in an
increase in tensile strength and they became stress-hardened, while submersion in
hypertonic solutions caused a decrease in tensile strength.
Video microscopy was employed to view the dynamics of tissue failure during
tensile fracturing of tissue slices of pear [47]; this method gave the added dimension
of time to texture assessment and allowed viewing of cell changes during deforma-
tion of living tissue. Time is an important concept since the sensation of texture
occurs over the period of time required for mastication.
‘Forcelle’ is a small pear with brownish yellow skin. The fresh skin has a regular,
reticulated appearance throughout plus larger, rounded cracks, or lenticels (Figure
18.12a). Extended, refrigerated storage, for a period of about a month, resulted in
a soft rot at the blossom end of the fruit. Portions of the rotted skin and the tissue
underneath were studied by SEM. The wax seemed to be completely destroyed and
the skin had a reticulated appearance due to cracking that outlined groups of epi-
dermal cells. The reticulations were different and much farther apart in the aged
fruit (Figure 18.12b) than those on the fresh sample. A closer view revealed that the
reticulations in the fresh fruit had a fibrous nature that connected the wax plates
FIGURE 18.11 (Opposite page)Scanning electron micrographs of cross sections of kiwi-
fruit. (a) Fresh cross section of the outer pericarp showing a mixture of large and small cells
in the flesh and the radially compressed cells in the flesh near the surface. (b) Aged cross
section showing areas of further compression resulting from aging. (c) Fresh fruit periphery
showing extent of compression of cells. (d) Aged fruit periphery showing more compression
and cell damage. (e) Fresh fruit just beneath surface periphery showing starch granules and
intact but slightly radially compressed cells. (f) Aged fruit of a similar area as in e showing
more compression, damaged cells and fewer starch granules than in the fresh sample; cell
wall thickening is also apparent. (g) Fresh sample; cells in the inner portion of the outer
pericarp showing regular shapes and starch granules. (h) Aged sample; cells in the inner
portion of the outer pericarp showing regular cell shapes and the lack of starch granules; cell
walls might be slightly thicker.