In an ongoing study researchers at Norwegian Institute of Fisheries Research and Aquaculture (NIFRA) found salt-cured cod that is desalted industrially and sold as chilled products may be full ofre-activated pathogenic bacteria. Even worse, the ready made meal product may become unsafe before being spoiled, due to the particular salt makeup of the product, NIFRA found.
The research is being conducted due to the growing use of desalted cod for the ready made meal market, NIFRA said.
Salt-cured cod, also called bacalao and klippfish, is produced in the North Atlantic countries and has been an important part of the Latin diet for centuries. Salt-cured cod contains between 15 percent to 20 per cent salt and must be desalted by consumers before consumption. Such cured cod is generally safe to eat as the salt usually forms an effective barrier for pathogenic bacteria.
"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,"NIFRA said in a statement.
However the salt content in ready-to-use products of salt-cured cod is only about three per cent and the bacteria are then able to grow if the desalted product is stored. The study found that bothStaphylococcus xylosus and Listeria innocua can survive for at least three weeks in cod juice with 21 per cent salt. However the bacteria are not able to grow at such high salt concentrations.
The research found the bacteria become re-activated when the salt content is reduced for ready-to-use products. The bacterial may reach dangerously-high levels within 10 days of chilled storage,NIFRA found.
"Based on growth kinetics, they may reach infective dose within approximately 10 days of chilled storage," NIFRA said. "Thus, the products may become unsafe before they areconsidered spoiled as determined by normal sensory assessment."
The shelf life of desalted cod is limited by the specific spoilage bacteria Psychrobacter sp. These bacteria can be inhibited by applying vacuum packaging and some food additives, leading to ashelf life of about two weeks. Such combination of methods is referred to as "hurdle technology". If unpreserved, desalted cod products have maximum one week shelf life when stored at 4C,NIFRA said.
"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 makingthe products safe," NIFRA concludes.