Effect of controlled atmosphere storage, modified atmosphere packaging and gaseous ozone treatment on the survival of Salmonella Enteritidis on cherry tomatoes

Abstract

In recent years, outbreaks of infections associated with raw and minimally processed fruits and vegetables have been reported. 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 to compare the results with those of air storage at 7 and 22 °C. During MAP, the gas composition equilibrated to 6% O 2/4% CO 2. CO 2 level was maintained as 5% through the term of CA storage at 7 and 22 °C. 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 log 10 cfu/tomato survived on tomato surfaces with an approximate decrease of 4.0–5.0 log 10 cfu/tomato in population within the storage period; however, in the case of initial population of 3.0 log 10 cfu/tomato, cells died completely on day 4 during MAP storage and on day 6 during both 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 and in CA. 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 log 10 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. During the research, the effect of ozone treatment (5–30 mg/l ozone gas for 0–20 min) was also considered for surface sanitation before storage. Gaseous ozone treatment has bactericidal effect on S. Enteritidis, inoculated on the surface of the tomatoes and can be used for surface sanitation of S. Enteritidis on tomatoes before storage at different conditions. Ten mg/l ozone gas treatment with different time intervals of 5 and 15 min was found to be effective respectively on low and high dose inoculum levels of S. Enteritidis attached for 1 h. Another variable considered during ozone treatment was the 4 h attachment time.