The Effect Temperature and Time Has On The Survival of Inoculated Salmonella Typhimurium on Romaine & Green Leaf Lettuce

Salmonella colonizes the surface or internal area of leafy greens and the issue of contamination in leafy greens with pathogenic microorganisms has not been fully understood. Temperature can have an important impact on microorganism growth and persistence on ready to eat (RTE) produce. The objective of this study was to determine how 5 Degrees Celsius (Refrigeration Temp) and 21 degrees Celsius (Room Temp) effects the survival and potential growth levels of Salmonella Typhimurium on Romaine and Green Leaf lettuce surfaces. The abundance of Salmonella remaining after inoculation and incubation at the two temperatures was compared between replicates. It was hypothesized that of the two selected leafy greens, Romaine will maintain the highest levels of Salmonella abundance based on previous studies. It was also hypothesized that the 21 Degrees Celsius (Room Temp) will have the highest amount of remaining cells/area of leaf. The Romaine Lettuce exhibited the highest sustained Salmonella numbers during Weeks 2 & 3, especially after 3 weeks. The two temperatures did play a significant role into how many cells remained where 21 degrees Celsius in both leafy greens had the highest survival the Romaine lettuce maintained bacterial levels that were twice as high as the Green leaf lettuce numbers. While the 5 degrees Celsius prevented survival amount as expected in the first two weeks, the third week also showed significantly higher levels of Salmonella. These results emphasize proper refrigerator temperature storage that is not advisable for longer than two weeks with the RTE lettuce types examined here.