iv
In recent years, outbreaks of infections associated with raw and
minimally processed fruits and vegetables have been reported. Possible
sources for contamination are irrigation water, manure, wash water, handling
by workers and contact with contaminated surfaces. Pathogens can occur on
raw and minimally processed produce at populations ranging from 103 to 109
CFU/g and able to survive and sometimes grow under various storage
conditions. The objective of this study was to analyse the growth/survival of
Salmonella Enteritidis at spot-inoculated or stem-injected cherry tomatoes
during passive modified atmosphere packaging (MAP), controlled
atmosphere (CA) and air storage at 7 and 22° / C. Low density polyethylene
(LDPE) with a package size of 10x10 cm2 for 25± / 2 g tomatoes was used for
MAP storage in which the gas composition equilibrated to 6% O2/ 4% CO2
and a carbon dioxide incubator was used for CA storage in which the CO2
level was monitored and maintained as 5% through the term of storage at 7
and 22° / C. During the research, the effect of ozone treatment (5-30 mg/L
ozone gas for 0-20 min) was also considered for surface sanitation. The
results demonstrate that S.Enteritidis can survive and/or grow during the
storage of tomatoes depending on the location site of the pathogen on fruit,
suspension cell density and storage temperature. During MAP, CA and air
storage, S.Enteritidis with initial population of 7.0 log10 CFU/tomato survived
on tomato surfaces with an approximate decrease of 4.0-5.0 log10
CFU/tomato in population within the storage period / however, in the case of
initial population of 3.0 log10 CFU/tomato, cells died completely on day 4
during MAP storage and on day 6 during CA and air storage. The death rate
of S.Enteritidis on the surfaces of tomatoes that were stored in MAP was
faster than that of stored in air. Storage temperature was effective on the
survival of S.Enteritidis for the samples stored at ambient atmosphere / cells
died completely on day 6 at 7° / C and on day 8 at 22° / C. Stem scars provided
protective environments for Salmonella / an approximate increase of 1.0 log10
CFU/tomato in stem-scar population was observed during MAP, CA and air
storage at 22° / C within the period of 20 days. Cells survived with no
significant change in number at 7° / C. The development of the microbial
association in tomatoes was dominated by lactic acid bacteria (LAB). The pH
values of the tomatoes changed approximately from 4.0 to 3.0 during the
storage period. LAB grew well under all atmospheric conditions with or
without the presence of S.Enteritidis. Gaseous ozone treatment has
bactericidal effect on S.Enteritidis, inoculated on the surface of the tomatoes.
5 mg/L ozone gas treatment was not effective. 30 mg/L ozone gas treatment
affected surface color.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12605337/index.pdf |
| Date | 01 July 2004 |
| Creators | Das, Elif |
| Contributors | Gurakan, Candan |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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