456 Produce Degradation: Reaction Pathways and their Prevention
of Salmonella Montevideo in the core tissue of tomatoes remained constant during
storage of the tomatoes at 10°C for 8 d. However, populations of the pathogen in
tomatoes increased significantly during storage at 20°C (Zhuang et al., 1995). As
observed with E. coli O157:H7, the extent of growth was greater in the section portions
of the oranges. Growth of both pathogens in the section portions of oranges at 21°C
may be attributed to the location of the organisms at internal sites, which are separated
from the acid juice. The juice of oranges is retained within segregated vesicles. There-
fore, internalized bacteria may be able to grow in areas outside of intact vesicles.
The results of these studies involving oranges underscored the importance of
low temperatures for preventing growth of certain pathogens in fresh produce.
Additionally, pH microenvironments that are conducive to bacterial survival and
growth may exist in intact fruit. The results also confirm the findings of previous
research that demonstrate the growth of human enteric pathogens in tomatoes
(Asplund and Nurmi, 1991; Zhuang et al., 1995), melons (Golden et al., 1993), and
apples (Janisiewicz et al., 1999).
14.7 CONCLUSION
The internalization of bacteria in fresh fruits and vegetables may compromise the
shelf life and microbial safety of these products. Bacteria adhere to fresh fruit and
vegetables or infiltrate them with the ingress of water through natural openings or
at damaged sites on the produce surface. Bacterial infiltration is affected by the
temperature of water in contact with fresh produce, hydrostatic pressure, surfactants,
and type of cooling system used in postharvest processing. Infiltration of bacteria
into intact fruit occurs most often when warm fruit is washed in cold water. This
negative temperature differential makes the tissues of the fruit contract and drives
the uptake of water by the fruit. Bacterial infiltration can occur relatively rapidly
when intact fruits endure hydrostatic pressure depending on the depth of immersion
in water. Intact fruits may have pH microenvironments that are conducive to survival
of internalized bacteria. A multifaceted approach to prevent bacterial infiltration in
fresh produce should include good agricultural practices, thorough screening of
produce for visible damage, and a combination of interventions to destroy bacteria
and control temperature and hydrostatic pressure during postharvest processing.
14.8 FUTURE RESEARCH
Published studies on internalization of bacteria in fruits and vegetables have provided
some evidence on how bacteria infiltrate these products as well as survive and grow
within them. However, gaps in current knowledge on bacterial infiltration and inter-
nalization in fresh produce warrant further research in the following areas: (1) natural
occurrence of human enteric pathogens internalized in intact fruit and conditions
that facilitate internalization; (2) assessment of risk of foodborne illness from fresh
produce that are infiltrated by human pathogens; (3) optimum conditions of temper-
ature and hydrostatic pressure for preventing infiltration in various types of fruits
and vegetables; and (4) extent of survival of human enteric pathogens in various
types of fresh produce.