Karin Söderqvist (PhD student, Department of Biomedical Sciences andVeterinary Public Health, SLU, Uppsala, Sweden), Ivar Vågsholm (Professor in Microbial Food Safety, Department of Biomedical Sciences andVeterinary Public Health, SLU, Uppsala, Sweden), Susanne Thisted Lambertz (Microbiologist, The National Food Agency, Microbiology division, Uppsala, Sweden) and Sofia Boqvist (Associate Professor in Infectious Disease Epidemiology, Department of Biomedical Sciences andVeterinary Public Health, SLU, Uppsala, Sweden)
There is a trend towards healthier eating habits with increased consumption of fresh vegetables, often sold prepared and ready-to-eat (RTE). Consumers consider these products safe and healthy. However an increasing number of foodborne outbreaks have been associated with consumption of RTE salad. Foodborne pathogens may contaminate at several steps during the production of RTE salad, e.g. via contaminated water or cross-contamination from human handling, and there is no process in the production chain that inactivates pathogens. Consequently, the safety of RTE salad depends on good hygiene practices and a well-functioning cold chain. The aim of the study was to investigate the growth of different pathogens in RTE salad, mimicking recommended fridge temperature (8 degrees C) and temperature abuse (15 degrees C). Two matrices were studied; salad (baby spinach) and mixed salad (baby spinach and grilled chicken). Rifampicin-resistant strains of Salmonella typhimurium, Listeria monocytogenes and pathogenic Yersinia enterocolitica together with a green fluorescent protein (GFP)–labeled strain of Escherichia coli O157:H7 were inoculated in low numbers and enumerated after 3 and 7 days. The results demonstrated that storage of mixed salad at 15 degrees C strongly supported growth of E. coli, L. monocytogenes and Y. enterocolitica. For L. monocytogenes and Y. enterocolitica growth was also supported in mixed salad at 8 degrees C. Cold storage of RTE salad is essential to reduce the risk of foodborne disease and for mixed RTE salad the recommended storage temperature should be lower than 8 degrees C –the current recommended temperature in Sweden.