Growth potential of Salmonella and Listeria monocytogenes in ready-to-eat lettuce and collard greens packaged under modified atmosphere and in perforated film.

This study was aimed at determining the effects of different storage scenarios on the growth potential of Salmonella strains and Listeria monocytogenes in ready-to-eat (RTE) mixes of iceberg and crisp lettuces (Lactuca sativa) and collard greens (Brassica oleracea). Vegetables were submitted to minimal processing, experimentally contaminated to achieve 10(1) and 10(2) CFU/g, packed under modified atmosphere and in perforated film, and submitted to the following storage scenarios: I = 100 % of the shelf life (6 days) at 7°C; II = 70 % of shelf life at 7°C and 30 % at 15°C; III = 30 % at 7°C and 70 % at 15°C; IV = 100 % at 15°C. Higher populations of Salmonella were observed in lettuce mixes than in collard greens; the opposite occurred with L. monocytogenes. Keeping the RTE vegetables at 15°C during the whole shelf life (scenario IV) or part of it (scenarios II and III) markedly influenced the growth of both pathogens in most of the scenarios studied (P < 0.05). Growth potentials of strains of Salmonella and L. monocytogenes were significantly different depending on the scenarios in samples packed with perforated film in comparison to those stored under modified atmosphere (P < 0.05). The findings indicate that even contamination as low as 10(1) CFU/g can lead to high populations if there is temperature abuse during storage (15°C). This study of the behavior of Salmonella and L. monocytogenes in RTE vegetables provides insights that may be useful in the development of strategies to control pathogen growth in these products.