542 Produce Degradation: Reaction Pathways and their Prevention
Kiwifruit is harvested at the mature but unripe stage, at which time the fruit is
quite firm. Softening occurs during the ripening process. Microscopy has been used
to document changes occurring during ripening at the microstructural level and
correlated with penetrometer tests to measure the hardness of the whole fruit. Unripe
kiwifruit has angular cells and, as they ripen, the cells become more rounded and
starch granules degrade.
Kiwifruit is composed of three distinct regions: outer pericarp, inner pericarp,
and core. Each tissue differs in composition and rate of change in cell wall compo-
nents. Cell walls thicken and undergo considerable change in all tissues of the fruit
during ripening [21,22].^ The thickening or swelling of cell walls in ripening kiwifruit
coincides with the solubilization of pectin [23]. Pectin hydrolysis and the modification
FIGURE 18.9Prepackaged peeled and washed baby carrot. (a) Outer surface of fresh carrot.
(b) Cross section of the outer layers of fresh carrot showing crushing of the cells due to initial
processing steps of peeling and washing. (c) Cross section of fresh carrot. (d) Cross section
of aged carrot showing cell wall breakage and cell collapse (arrows). (e) Aged carrot, close
view showing the effects of cell wall breakage. (f) Aged carrot, close view showing cell wall
breakage and cell collapse. (g) Fresh carrot cross section showing no cell wall breakage or
collapse. Magnification bars: a, 200 μm; b, 50 μm; c, d, 1 μm; e–g, 200 μm.