Growth and survival of Salmonella in modified atmosphere packaged rainbow trout (Oncorhynchus mykiss) fillets

The growth and survival of Salmonella in rainbow trout fillets stored under vacuum, aerobic conditions, or a modified atmosphere of carbon dioxide (CO₂):nitrogen(N₂) (60:40) with or without a carbonic acid dip treatment was evaluated at 3 and 10°C. In addition, the effect of these storage conditions on the growth of aerobic, psychrotrophic, lactic, and coliform bacteria was also examined.

The Salmonella inoculum level was approximately log 4 CFU/g trout, although direct plating resulted in initial counts of log 3.0 to 3.5 CFU/g. The growth of Salmonella at 10°C was significantly higher (p < 0.05) in trout held under vacuum and air packaging than in trout held under the CO₂- modified atmosphere. Salmonella numbers declined in the trout samples stored at 3°C, with significantly greater (p < 0.05) survival under air packaging than in vacuum and CO₂- modified atmosphere packaging. The growth of aerobic, psychrotrophic, lactic, and coliform bacteria in the trout fillets was significantly lower (p < 0.05) under the modified atmosphere of CO₂:N₂ (60:40) than air and vacuum packaging at 3 and 10°C with a shelf-life extension of approximately 3 days at 10°C and 9 days at 3°C. The carbonic acid dip had some initial effect upon the growth of aerobic and coliform bacteria at 10°C, although no extension of shelf life was evident.