Food Protection Trends - January/February 2021 - 51

of 5.10, 4.94, and 3.37 log CFU/g over 96 h, respectively.
Elevating temperature to 22°C and holding for 32 h did not
lead to a significant (P > 0.05) increase in SALM or STEC
populations compared with 10°C but did allow for significant
(P < 0.05) growth of LM (Table 3). Similarly, Neetoo et
al. (34) observed population increases for E. coli O157:H7
and Salmonella of 3.8 to 4.7 and 3.6 to 4.6 log CFU/g,
respectively, over an 8-day incubation period at 22°C.
Others have observed growth of LM on diced onion under
fluctuating temperature scenarios (27).
Pathogen response to temperature when inoculated onto
fresh-cut pepper was similar to that of onion, with significant
growth of LM at 5°C (2.36 log CFU/g growth over 168
h), but not of SALM and STEC, and a dramatic increase in
population across all pathogens at 10°C (Δ-log CFU/g of
5.40, 5.07, and 4.83 over 96 h for SALM, STEC, and LM,
respectively) (Table 3). Growth of pathogens on fresh-cut
pepper at 22° was not significantly (P > 0.05) different from
10°C. Castro-Rosas et al. (17) similarly noted growth of
Salmonella and E. coli on sliced chili pepper at 25°C, with
growth of ~4 log CFU on pepper slices after 24 h. Unlike
our results, however, Castro-Rosas et al. (17) observed a
1- to 2-log CFU reduction in population of Salmonella or E.
coli strains on pepper slices after 6 days at 3°C, presumably
due to differences in either bacterial strains or incubation
temperature, or perhaps due to antibacterial activity
associated with sliced chilies (28). Castro-Rosas et al. (17)
noted that survival of even a small number of Salmonella
or other pathogens under refrigeration presents a serious
health hazard to consumers due to the low infectious dose
associated with many foodborne pathogens.
Holding of fresh-cut cucumber at 5°C allowed for
significant growth of both SALM and LM (Δ-log CFU/g of
1.30 and 1.96, respectively) (Table 3). As seen with onion
and pepper, increasing hold temperature to 10°C significantly
(P < 0.05) increased pathogen growth over 5°C. Holding
inoculated fresh-cut cucumbers for 96 h at 10°C resulted
in values of 5.24, 5.25, and 4.19 Δ-log CFU/g for SALM,
STEC, and LM, respectively. Whereas growth of SALM
and STEC at 22°C was not significantly (P > 0.05) different
from 10°C, growth of LM was significantly higher at 22°C on
fresh-cut cucumber (4.64 log CFU/g) over 32 h (Table 3).
Bardsley et al. (7) found that LM populations significantly
increased on sliced cucumbers (2.9 log CFU/g) held at 4°C,
whereas Salmonella populations significantly decreased (1.3
log CFU/g). The extended hold time in the Bardsley et al.
(7) study (21 days) may account for the difference in results.
Our results are, however, consistent with what others have
observed for survival patterns of SALM and LM inoculated
into cucumber tissue stored at 10°C (18), 23°C (7), or 25°C
(22), but contrary to what has been observed for Salmonellainoculated cucumber slices stored 48 h at 4°C, wherein no
change in pathogen population was observed (22). The
difference in study results can be explained by a difference

in strain selection and study methodology. As with other
produce items in this study, pathogen population numbers
on chopped cucumber did not decrease on holding at 5°C;
instead; at least a doubling of inoculum population density
was observed for SALM, STEC, and LM (Δ-log > 0.3 log
CFU/g) (Table 3). The ability of LM and SALM to grow
on sliced cucumbers in short amounts of time at ambient
temperatures (1 day) and to survive on sliced cucumbers
past the recommended shelf life at refrigeration temperatures
highlights the need to reduce the likelihood of contamination
events throughout the cucumber supply chain (7).
Tomato is listed as a TCS food in the FDA Food Code
and was included in this study as a positive control. Tomato
tissue pH averaged 4.4 across trials. As expected, holding
fresh-cut tomatoes for up to 196 h at 5°C did not allow
for significant pathogen growth (Table 3). At an abusive
refrigeration temperature (10°C), there was significant (P <
0.05) growth of SALM on fresh-cut tomato (4.36 log CFU/g
over 96 h) and a detectable increase in STEC that proved not
significant (P > 0.05). At 22°C, both SALM and STEC grew
robustly on fresh-cut tomato (Δ-log CFU/g of 5.17 and 4.45,
respectively) over 32 h.
Beuchat et al. (12, 13) have investigated pathogen growth in
tomato flesh. Acid-adapted and nonadapted strains of Salmonella
were inoculated into 'Roma' tomato pulp (pH ~ 4.3) that was
subsequently stored at 4, 12, and 21°C. Salmonella populations
increased ~2 log CFU/g over 10 days at 12°C, but no population
increase was observed at the first sampling point (3 days). A
population increase of 3 to 4 log CFU/g was noted by day 3
for tomato pulp stored at 21°C, with little further change noted
from day 3 to day 10. We observed greater increases in SALM
populations inoculated onto fresh-cut tomatoes and held at 10
or 22°C, likely due to differences in study methodology. Separate
investigations into survival of E. coli O157:H7 inoculated into
processed whole tomato (canned, peeled whole tomatoes,
no other ingredients, pH 4.6) did not show marked variation
in pathogen count at 4°C over time. At 25°C, however, the
population of test strains increased by ~3 log CFU/g in the first
48 h (19), survival trends similar to what we observed.
Fresh-cut tomato did not support significant growth of LM
at any holding temperature (Table 3). When Beuchat et al. (12)
investigated survival of LM on chopped tomatoes held at 10
or 21°C, they observed no population changes over the first 4
days of storage at 10°C and an ~1-log population decrease at
21°C over the first 48 h. In the same study (12), when LM was
inoculated into commercially processed tomato juice (pH 4.21),
pathogen population did not change when held at 5°C for 7 days.
Holding fresh-cut produce for 196 h at 5°C failed to
prevent significant (P < 0.05) growth of LM on onion,
pepper, and cucumber (Δ-log CFU/g of 1.37, 2.36, and 1.96,
respectively). Significant growth of SALM on cucumber was
also observed (Table 3, 1.30 log CFU/g). Overall, growth
of pathogens on fresh-cut produce was not significantly
different (P < 0.05) at 10 and 22°C for SALM and STEC

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Food Protection Trends - January/February 2021

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