When apricot fruit was stored at 20 °C, Salmonella populations on
apricots also decreased; however, the reduction of Salmonella populations
on fruit treated with 74 mJ/cm2 was the lowest during storage
(Fig. 7). Even though UV-C treatment at 74 mJ/cm2 reduced Salmonella
populations by 0.7 and 1.4 log CFU/fruit when enumerated on TSA and
XLT-4, respectively, in comparison with non-treated controls on the day
of treatment, there was no significant difference between non-treated
controls and fruit treated with 74 mJ/cm2 after 8 days at 20 °C. On the
other hand, Salmonella populations on fruit treated with 442 mJ/cm2
UV-C decreased rapidly during storage. Following 8 days at 20 °C, populations
of Salmonella on fruit treated with 442 mJ/cm2 were 2 and
4 log CFU/fruit lower than those from the non-treated fruit enumerated
on TSA and XLT-4 media, respectively.
Our results indicate that E. coli and Salmonella survived well on nontreated
apricots during storage either at 2 °C or 20 °C. More than
5 log CFU/fruit of E. coli and Salmonella spp. remained on the fruit
after 8 days of storage at 20 °C or 21 days at 2 °C. Following UV-C treatment,
particularly at a dose of 442 mJ/cm2
, bacteria on apricots decreased
more rapidly than those on non-treated fruit during post-UV
storage at either 2 °C or 20 °C. Escalona et al. (2010) found that UV-C
radiation at doses of 2.4–24 mJ/cm2 reduced S. enterica loads during
the first 4 days of a 14-day storage study at 5 °C, after which, the bacterium
increased significantly on radiated leaves when compared to the
control. The same authors (Escalona et al., 2010) also found that UV
treatment (2.4–24 kJ/m2
) reduced Listeria monocytogenes populations
by 2 logs on cut spinach. However, after 14 days of storage at 4 °C, the
control reached 4.2–4.7 log CFU/g, while UV-C-treated leaves increased
to 3.6–4.5 log CFU/g, indicating that the pathogen grew faster on UVtreated
leaves than on the control. The dose used in our present study
was much higher than those used by Escalona et al. (2010). Our results
demonstrated that a lower dose of UV (i.e., 74 mJ/cm2
) increased reductions
of bacterial populations only for Salmonella spp. stored at 2 °C.
Higher doses of UV-C (i.e., 442 mJ/cm2
) increased lethality of UV-C
during storage, regardless of storage temperature. Sommers et al.
(2009) found that L. monocytogenes levels on UV-C-treated (1 J/cm2
)frankfurters that contained potassium lactate and sodium diacetate
decreased much more rapidly than those on non-UVC-treated frankfurter
samples during 8 weeks of refrigerated storage.