The scientific explanation is the following:
Salt-curing is usually considered as an effective barrier for pathogenic bacteria, and as a consequence, any pathogenic bacteria detected in desalted fish have been assumed to be recontaminations during the desalting operation. However, new information from the present study is that both Staphylococcus xylosus and Listeria innocua, being surrogates for the human pathogenic bacteria S. aureus and L. monocytogenes, can survive for at least 3 weeks in cod juice with 21 % salt. The bacteria are not able to grow at high salt concentrations. They do not cause illness when present in low numbers, and traditional salt-cured cod is therefore a safe product, even if some bacteria are transferred during the heavy salting stage. The salt content in ready-to-use products of salt-cured cod, on the other hand, is only 3 %, and the bacteria are then able to grow if the desalted product is stored. Based on growth kinetics, they may reach infective dose within app 10 days of chilled storage. Thus, the products may become unsafe before they are considered spoiled as determined by normal sensory assessment.
The shelf life of desalted cod is limited by the specific spoilage bacteria Psychrobacter sp. It has previously been shown that these bacteria can be inhibited by applying vacuum packaging and some food additives, leading to a shelf life of app 2 weeks. If unpreserved, desalted cod products have maximum one week shelf life when stored at 4 °C. Preserved products are more convenient for distribution, but the present study indicates that they may become unsafe before being spoiled. It is therefore recommended to retain the short shelf life until better methods, like the possibilities for applying hurdle technologies, have been demonstrated to be effective in making the products safe. This will be pursued in further SEAFOODplus studies in the project 4.2 HURDLETECH.
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