NORWAY - If nitrogen is replaced with high oxygen in the package, cod can be kept fresh for longer, according to research from Norwegian institute Nofima.
Researcher Anlaug Ådland Hansen and her colleagues at Nofima analysed the bacteria found in cod wrapped fresh and researched how the emergence of these can be prevented through optimum packaging methods.
By taking samples of fresh cod fillets, they found three types of bacteria that we know is especially unfortunate for cod in the development of odour and taste.
The three types are Photobacterium, Pseudomonas and Shewanella, and are found naturally in fish, but the amount of bacteria in the packs by the time they end up in the store varies.
The production environment is important
"What amount of bacteria supplied into the package depends on the cleaning procedures during the production process. It is clear the production environment influences which bacteria we find," said Ms Hansen.
The researcher's mission is to ensure that the different bacteria have as poor growing conditions as possible inside the fish packaging.
Ms Hansen conducted experiments with different packet gases to see how it affected the emergence of the different types of bacteria on fresh cod.
Previously it has been shown that cod should preferably be frozen to kill the bacterium Photobacterium, the scientists found that changing the gas mixture in the packaging may have similar results, especially with this type of bacterium.
"The more we know about the enemy, the easier we can fight it," Ms Hansen said.
The new knowledge comes from a large research program on live storage, called CATCH. The program runs for four years and is funded by 29 million via Bionær program in the Research Council.
Composition of the gas mixture
The most common packaging gas used in Norway today consists of 60 per cent carbon dioxide and 40 per cent nitrogen.
"The normal packet gas mixture has had some effect on the Photobacterium, but replacing nitrogen with high oxygen inhibited this particular bacterium even more. This new package gas mixture also has inhibitory effects on other types of bacteria we found on the fish, and means the industry henceforth should focus on high oxygen in the packaging process," the researcher said.
She estimates that shelf time in stores can be increased by up to 20 per cent, if all conditions are favourable for good storage.
"The flora in the raw material, the choice of packaging method and storage temperature are critical factors for durability. The lower bacterial counts are in the initial product, the longer durability can be achieved. Selecting additionally the best packing method gives optimum quality and maximum durability."
Ms Hansen is somewhat skeptical that the current packing methods extends the shelf life of fresh cod to 10 days.
"With the knowledge from this project I would say that the current practice of 10 day shelf life, are slightly in excess. High oxygen does, however, have the potential to increase shelf life. Optimally, if you have low bacterial levels in the raw material and for example, choosing high oxygen, you can achieve 12-day shelf life," said the researcher.
Selection of packaging is also significant in the overall picture.
"Many different factors come into play on durability, such as packaging barrier properties at the storage temperature. Then it is important to know the barrier properties of the finished package under real storage conditions," the researcher explained.
TheFishSite News Desk