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Protective Atmospheres |
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In order to maintain the high quality of fresh fish products, it is crucial to maintain temperatures as close to 32 °F as possible. In combination with the right MAPAX® gas mixture, shelf life can be extended by a few valuable extra days. One condition, naturally, is an unbroken chain of refrigeration. Cod, flounder, salmon and tuna are examples of fish that can be stored at 32 °F for twice as long in a modified atmosphere than in air. |
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The presence of carbon dioxide is necessary to inhibit growth of common aerobic bacteria such as Pseudomonas, Acinetobacter and Moraxella. At levels above 20% in sufficiently large package volumes, growth is primarily inhibited in fish because carbon dioxide lowers the pH level of the tissue surface. The carbon dioxide concentration is normally 50% in practical situations. Depending on the storage temperature (32 –35 °F), modified atmosphere packaging prolongs the shelf life by 3 to 5 days compared with the shelf life of raw fish in a tray with film overwrap. Excessively high concentrations can produce undesirable after-effects in the form of lost tissue liquid or, in the case of crabs, an acidic or sour taste. |
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Oxygen can be used as a component of a modified atmosphere to avoid color changes and pigment fading in fish and seafood. The gas is also used to prevent growth of anaerobic microorganisms such as Clostridium, which can produce toxins. The risk, however, for Clostridium growth in correctly modified atmosphere packaged fish with short shelf life is negligible. If the temperature is kept below +38 °F, there can be no growth. To combat rancidity, oxygen should not be used in packaging of high-fat fish. In this case, nitrogen is more suitable. |
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Product | Fatty fish | Lean fish | Cooked fish products |
MAPAX Gas mixture | 60 - 70% CO2 and
30 - 40% N2 | 30 - 40% O2 and
30 - 70% CO2 and
0 - 30% N2 | 20% CO2 and
80% N2 |
Gas volume per Product weight | 200 - 300 ml per 100 g fish | 200 - 300 ml per 100 g fish | 50-100 ml per 100 g prod. |
Typical shelf-life | 3 - 5 days in air
5 - 9 days with MAP | 3 - 5 days in air
5 - 9 days with MAP | 2 - 4 days in air
4 - 5 weeks with MAP |
Typical material* | OPET/PVdc/PE-PVC/PE | OPET/PVdc/PE-PVC/PE | OPET/PVdc/PE-PVC/PE |
Typical machine | Deep-draw machine | Deep-draw machine | Deep-draw machine |
Storage temp. | +32 to +38 oF | +32 to +38 oF | +40 to +45 oF |
*PVC is being replaced by APET or PS/EVOH, PVdC is being replaced by EVOH or OPA |
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