Growth of the psychrotrophic pathogens Aeromonas hydrophila, Listeria monocytogenes and Yersinia enterocolitica on smoked blue cod (Parapercis colias) packed under vacuum or carbon dioxide

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Abstract
Summary: Commercially prepared smoked blue cod (Parapercis colias) was divided into 25‐g subsamples which either served as uninoculated controls or were inoculated with a two‐strain cocktail of one of the psychrotrophic pathogens Aeromonas hydrophila, Listeria monocytogenes or Yersinia enterocolitica. The inoculated and control subsamples were then either vacuum or carbon dioxide packed prior to storage at 3°C or −1.5°C. After various periods of storage, triplicate samples from both packaging treatments for the three pathogens and the corresponding uninoculated controls were removed and subjected to microbiological analysis. None of the three pathogens was found as a natural contaminant of the commercial product. In vacuum‐packs all three psychrotrophic pathogens were able to grow during storage at 3°C. Reduction of the storage temperature to − 1.5°C retarded but did not prevent pathogen proliferation. Under carbon dioxide, only A. hydrophila was able to grow at 3°C and then only after a 21‐day lag period. None of the psychrotrophic pathogens was able to grow under carbon dioxide at − 1.5°C. With the possible exception of A. hydrophila, pathogen numbers did not decline in carbon dioxide packs during 155 days storage at − 1.5°C. It is concluded that provided gross contamination with psychrotrophic pathogens prior to packaging does not occur, a 100% carbon dioxide controlled atmosphere can be used to extend the product life of smoked blue cod during storage at or below 0°C without compromising its safety in respect to growth of A. hydrophila, L monocytogenes or Y. enterocolitica.

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