Modified Atmosphere Packaging of Raw Fish and Seafood

Extending the shelf-life of fresh fish and seafood products

Fresh fish and seafood rapidly lose their original quality as a result of microbial growth and enzymatic processes. This is due to their high water activity, neutral pH (where microorganisms thrive), and the presence of enzymes, which rapidly undermine both taste and smell. The breakdown of proteins by microorganisms gives rise to unpleasant odors.

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, resulting in the production of undesirable fishy odours. Oxidative rancidity of unsaturated fats in oily fish such as salmon, herring and mackerel also results in other additional offensive odours and flavours. Fish such as herring and trout can turn rancid even before microbial deterioration is detectable.

In order to maintain the high quality of fresh fish products, it is absolutely essential that the temperature is kept as close to 0°C as possible. The right MAP modified atmosphere packaging gas mixture, combined with proper temperature control, can extend the shelf life of fish by a few more days, assuming of course, that the refrigeration chain is unbroken.

MAP modified atmosphere packaging is a very effective technique for delaying the 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. To avoid rancidity, oxygen should not be used to package oily fish. The inclusion of CO2 is necessary for inhibiting common aerobic spoilage bacteria, such as Pseudomonas species (in open air).

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

Oxygen can be used within a modified atmosphere pacakging mix to avoid discolouration and pigment fading in fish and seafood. Oxygen is also used to prevent the growth of anaerobic microorganisms such as clostridium, which can produce toxins.

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.

General Information for Modified Atmosphere Packaging of Raw Fish and Seafood