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Sub-Chilled and modified atmosphere packaging extend the shelf life of salmon

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By Milthon Lujan

The waste of food is one of the major global challenges, but innovative packaging and sub-chilled techniques are at the forefront to address these issues. However, the effectiveness of food packaging material and its ability to preserve product quality largely depends on its barrier properties.

Researchers from Nofima AS studied the effect of subcooling on whole eviscerated salmon and sub-chilled storage at -1°C in modified atmosphere packaging using two recyclable mono-material trays (CPET, HDPE).

Modified Atmosphere Packaging

Modified Atmosphere Packaging is a popular method for fish, utilizing various gases to delay microbial growth and unwanted chemical reactions. For highly perishable products like fish and seafood, the gas and water vapor permeability of the material is crucial.

By modifying the air mixture inside the package, we can inhibit bacteria and keep the fish fresh for a longer period. Carbon dioxide (CO2) plays a primary role, eliminating bacteria and slowing their growth. Nitrogen (N2) acts as a supportive companion, filling the package and preventing it from collapsing. However, the right balance and combination of gases depend on the type of fish.

Fatty fish like salmon require less oxygen (O2) to avoid unwanted changes.


Have you ever heard of “sub-chilling”? It’s a food preservation method that lowers the internal temperature of the product below 0°C.

This method decreases the fish’s internal temperature just below the freezing point without forming ice crystals. This keeps its flavor fresher and firmer than traditional ice storage.

And the best part? You can use chilled seawater (RSW), an eco-friendly alternative to bulky ice that takes up less space and reduces costs. Recent studies have shown that subcooling whole eviscerated fish in RSW at -1°C provides higher water retention capacity and comparable quality to ice storage.

It’s important to note that subchilling is also known as super-chilling, deep chilling, ultra chilling, surface freezing, and partial freezing.

Evaluated Parameters

Researchers obtained eighty eviscerated Atlantic salmon, divided into 2 groups. Ten from each group were marked and weighed to monitor weight changes over 7 days.

“One group was packed in expanded polystyrene (EPS) boxes with ice (n = 30) and kept in a cold room at 0°C. The other group (n = 45) was submerged in a 1000 L polyethylene tank containing laboratory-made saltwater (3.5% salinity) for 4 days, before draining the saltwater and placing the fish in EPS boxes without ice for 3 days at -1°C. The saltwater temperature was kept at -1°C,” they reported.

The scientific team measured quality parameters, including water retention properties, salt content, color, texture, lipid oxidation, sensory and microbiological shelf life, and oxygen transmission rate for the packages.

Key Findings

The main results of the study were:

  • Subcooling resulted in a 0.4% weight increase.
  • Improved water retention capacity.
  • Higher salt content.
  • Subcooled fish provided significantly better sensory quality.
  • Microbiological shelf life extended up to 49 days.


The study also compared two recyclable tray materials: CPET and HDPE.

While CPET had slightly higher drip loss, it also had a lower lipid oxidation rate, meaning the salmon stayed fresher.


“Our results demonstrated the feasibility of significantly extending shelf life with subcooling, eliminating the need for ice,” conclude the researchers. Additionally, the study shows that the use of recyclable trays contributes to a circular economy without compromising food quality.

This research highlights that subcooling and recyclable packaging offer a powerful combination to combat food waste, delight salmon lovers, and protect our planet.

The study was funded by the Research Council of Norway and Nofima.

Bjørn Tore Rotabakk
Department of Processing Technology
Nofima AS, 4021 Stavanger, Norway

Reference (open access)
Chan, Sherry Stephanie, Birgitte Moen, Trond Løvdal, Bjørn Roth, Astrid Nilsson, Marit Kvalvåg Pettersen, and Bjørn Tore Rotabakk. 2024. “Extending the Shelf Life of Atlantic Salmon (Salmo salar) with Sub-Chilled Storage and Modified Atmosphere Packaging in Recyclable Mono-Material Trays” Foods 13, no. 1: 19. https://doi.org/10.3390/foods13010019

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