Purpose: To examine the fate of Salmonella enterica in a mixed ingredient salad containing fresh-cut lettuce, cheddar cheese and cooked chicken.
Methods: Eight mixed salads (500 g) in polyethylene trays containing fresh-cut Romaine lettuce overlaid with cooked chicken and cheddar cheese were obtained from a local retailer on two occasions. The ingredients were separated, one third of the lettuce from each salad was discarded and replaced with an equivalent weight of lettuce washed in chlorinated (70 ppm Cl) water after inoculation with a five strain cocktail of S. enterica. The cooked chicken and cheese were returned to one half of the salads and S. enterica populations were estimated on XLD agar in each salad immediately and after 3 days of storage at 6°C or 14°C.
Results: S. enterica populations declined slightly in salads stored at 6°C without added ingredients (2.19 ± 0.11 to 1.52 ± 0.51 log CFU/g) and with cooked chicken and cheese (1.76 ± 014 to 1.08 ± 0.15 log CFU/g). In contrast, S. enterica grew in salads stored at 14°C and the population increase was significantly (P < 0.05) higher in salads with added ingredients (4.16 ± 0.45 log CFU/g) than lettuce alone (1.75 ± 0.58 log CFU/g).
Significance: The finding that growth of S. enterica was accelerated in a mixed ingredient salad highlighted the need to ensure these products are formulated with ingredients free of enteric bacterial pathogens and emphasized the critical importance of temperature control during their storage and distribution.