448 Produce Degradation: Reaction Pathways and their Prevention
into these fruits. Almed et al. (1973) reported that damage to citrus fruits during
harvesting allowed the entry of spoilage microorganisms.
14.4.1.4.3 Harvesting and Postharvest Operations
Mechanically harvested fruits are relatively more susceptible to splitting, puncturing,
and bruising compared to fruits harvested manually. For example, the mechanical
harvesting of citrus produces a higher incidence of fruits with attached stems (more
than 1 cm long) that can inflict puncture wounds on other fruits during handling.
Manual harvesting of citrus fruits results in more fruits that endure “plugging” or
removal of part of the peel at the stem (Almed et al., 1973). Carballo et al. (1994)
noted that field-packed bell peppers sustained fewer bruises than peppers packaged
in a packing house. Forceful contact of fruits with hard surfaces during harvesting,
high-pressure spray washing, processing, packaging, and storage may cause bacteria
to become embedded in sites just beyond the surface of the fruits. Petracek et al.
(1998) suggested that high-pressure spray washing of citrus does not generally result
in visible damage to sound fruit; however, this process will rupture fruit in areas
that were previously injured.
When fruits endure pressure on their surfaces via rubbing or other types of
cleaning actions such as brushing, bacterial cells may be forced into the layer of
natural wax platelets and in cracks on the skin surface. Kenney et al. (2001) used
CSLM to observe the location of E. coli O157:H7 cells on the surface of artificially
inoculated, bruised Red Delicious apples. The inoculated apples were washed and/or
rubbed with a polyester cloth then checked to ascertain whether the treatments
introduced cells into areas beyond the surface of the skin. The researchers found
that there was no significant difference in the location of E. coli O157:H7 cells on
or in undamaged and bruised apples that were not rubbed or washed. Cells adhered
preferentially to the edges of cuticular wax platelets and in gaps between the plate-
lets. However, cells on the surface of rubbed apples were sealed in the naturally
occurring cracks on the wax platelets. These cells most likely became embedded in
the wax platelets when pressure was applied to the surface of apples during rubbing.
14.5 INFILTRATION OF BACTERIA IN FRUITS AND VEGETABLES
Bacteria cells suspended in water may infiltrate the internal tissues of fruits and
vegetables during contact with the surfaces of these products. Research conducted
as early as the 1960s demonstrated the internalization of bacteria in otherwise healthy
tissues of vegetables (Samish, et al., 1961, 1963). In the natural environment bacterial
infiltration may occur when dew, rainwater, or irrigation water accumulates on the
surface of fruits and vegetables. Also, contact between fallen fruit and ground water
could facilitate bacterial infiltration. Several studies have attempted to determine
whether bacteria infiltrated fruits and vegetables under natural environmental con-
ditions. Solomon et al. (2002) demonstrated that when lettuce was grown in soil
with artificially contaminated manure or irrigation water, E. coli O157:H7 can
infiltrate the root system and migrate throughout the edible portion of the plant.
Seeman et al. (2003) investigated the internalization of E. coli ATCC 25922 in whole
apples in a controlled outdoor setting. Apples of three varieties (Red Delicious,