Raw, High-fat, Oily Fish

Food items: Bluefish, Carp, Eel, Greenland Halibut, Herring, Mackerel, Pilchard, Rock Salmon, Salmon, Sardines, Shad, Sprats, Swordfish, Trout, Tuna, Whitebait, other items

Recommended gas mixture
40% CO₂ 
60% N₂

With some residual oxygen

The gases and mixtures listed above are for general guidance. To identify the optimum gas for your product and process, we recommend you undertake a product trial, with the help of an Air Products MAP gas specialist. 

Storage temperature
Legal maximum*: 8° C
Recommended: -1° C to +2° C

Achievable shelf-life
In air: 2-3 days 
In MAP: 4-6 days

Principle spoilage organisms and mechanics
Pseudomonas species (in air), Lactic acid bacteria, Enterobacteriaceae, Shewanella species, Photobacterium species, Aeromonas species.

Food poisoning hazards include
Clostridium botulinum (non-proteolytic E, B and F), Vibrio parahaemolyticus, Salmonella species and Listeria monocytogenes.

Typical MAP machines
Retail
• TFFS – Thermoform-fill-seal
• PTLF – Preformed tray and lidding film

Typical types of package
Retail: Tray and lidding film

Examples of typical MAP materials
Retail
Tray: 
• PVC/PE 
• APET/PE 
• HDPE 
• EPS/EVOH/PE

Lidding and/or pillow pack film:
• PET/PE-EVOH-PE
• OPA/PE-EVOH-PE
• OPP/PE-EVOH-PE 
• PET/PVdC/PE

The principal spoilage mechanisms affecting the quality of fish and seafood are the result of microbial and oxidative activities. Fish and seafood products are very perishable due to their high aw, neutral pH, and presence of autolytic enzymes which cause the rapid development of undesirable odours and flavours.

Fish normally have a particularly heavy microbial load owing to their cold water origins, method of capture and transport to shore, evisceration and retention of skin in retail portions. Microbial activity causes a breakdown of fish protein, with resulting production of undesirable fishy odours. Oxidative rancidity of unsaturated fats in oily fish also results in other additional offensive odours and flavours.

MAP is a very effective technique for delaying microbial spoilage and oxidative rancidity in fish and seafood products. MAP is particularly effective at extending the shelf-life of white fish products. For white fish, crustaceans and molluscs, a gas mixture containing 30% O₂  , 40% CO₂, and 30% N₂ is recommended. A gas mixture containing 40% CO₂ and 60% N₂ is recommended for oily fish products. The inclusion of CO₂ is necessary for inhibiting common aerobic spoilage bacteria, such as Pseudomonas species (in air).

However, for retail packs of fish and other seafood, too high a proportion of CO₂ in the gas mixture can induce pack collapse, excessive drip, and in cold-eating seafood products such as crab, an acidic, sherbet-like flavour.

O₂ is necessary to prevent the growth of Clostridium botulinum type E, colour changes and bleaching, and reduce drip in white fish, crustacean and mollusc MA packs. However, O₂ is preferentially excluded from oily fish MA packs so as to inhibit oxidative rancidity. A gas/product ratio of 2:1 is recommended.

Only the highest quality fish and seafood should be used to benefit from the extended shelf-life advantages of MAP. The Achievable shelf-life will depend on the species, fat content, initial microbial load, gas mixture, and temperature of storage. The maintenance of recommended chilled temperatures and good hygiene and handling practices throughout the entire capture-to-consumption chain is essential for ensuring the safety and extended shelf-life of fish and seafood products.

* The Food Safety (Temperature Control) regulations 1995 states that the maximum Storage temperature for chilled perishable foods is 8°C. There will be flexibility to vary this when scientifically justified. For legal temperature storage requirements, please contact the Campden and Chorleywood Food Research Association.