Traditional cooling Archives

Color of supercooled gills

Published:

15/07/2020

Authors:

Gunnar Þórðarson, Margrét Geirsdóttir and Sigurjón Arason

Supported by:

AVS Fisheries Research Fund

Contact

Gunnar Þórðarson

Regional Manager

gunnar.thordarson@matis.is

The color of the gills has long been used to evaluate the freshness of fish, but it is known that during storage the color changes and they darken. When ultra-skinning of salmon was introduced, which improved the quality of production, billfish followed the short-rib method, where the gills darkened during cooling; but the color change can cause difficulties in the market and give the false impression that freshness is not good enough.

It was therefore important to get answers as to why this color change occurs during hypothermia, which is defined as cooling below 0 °C and less than or equal to 20% of the water content of the muscle being frozen. The research question was therefore whether it was the salt or the cold in the refrigerant that caused the color change. The result of the project is unequivocal that the cooling is the causative factor and the color of the gills changes when freezing during cooling which is based on a cooling medium of -2.5 °C and a cooling time of about 80 minutes.
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The color of the gills has long been used to evaluate the freshness of fish, but it is known that during storage, the color changes and they darken. When super chilling of salmon was introduced which improved the quality of production, a problem followed by the gills darkening during chilling; but the color change can cause difficulties in the market and incorrectly indicate that freshness is not satisfactory.

It was therefore important to obtain answers as to why this discoloration occurs during supercooling, which is defined as cooling below 0 ° C and less or equal to 20% of the water content of the muscle being frozen. The research question was whether it was the salt or the cold in the refrigerant that caused the color change. The result of the project is unequivocally that the cooling is the cause and the color of the gills changes when it freezes during cooling, which is based on a refrigerant of -2.5 ° C and a cooling time of about 80 minutes.

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The effect of mortality on fish quality ll

Post author By admin
Post date 15/08/2019

Published:

15/08/2019

Authors:

Gunnar Þórðarson, Sigurjón Arason

Supported by:

AVS Fisheries Research Fund (R 17 019-17)

Contact

Gunnar Þórðarson

Regional Manager

gunnar.thordarson@matis.is

The effect of mortality on fish quality ll

The purpose of the study was, on the one hand, to investigate the effect of supercooling on the death-hardening process of cod and salmon fillets and to compare with conventional cooling; and, on the other hand, to examine whether filleting at different times in the death solidification process (before mortality, in mortality and after the process ends) had a product quality. For salmon, a preliminary experiment was performed on which the main experiment was based, while in cod an experiment was performed on wild cod and farmed fish.

Supercooling of cod is based on cooling down to -0.8 ° C and salmon at -1.2 ° C, while conventional cooling is based on 0 ° C for both species. Differences between groups were examined and also differences within groups were compared. Small differences within groups indicate a more accurate and credible conclusion.

The results of a survey carried out by a sensory evaluation team show that the effect of supercooling is considerable as there is less contraction in the death solidification process, and the effect on quality is therefore smaller. There is a difference between wild cod and farmed cod, as it is known that the water content between cells is less in farmed development than wild. It might be interesting to look at the difference between farmed salmon and wild salmon, but that was outside the scope of this study.

It can be concluded that with supercooling it would be possible to process salmon for freezing to death without degrading quality, which could be important in the marketing of fresh products in the future, as the salmon could be processed immediately at slaughter and thus increase shelf life in foreign markets.

One of the aims of the project was to prepare promotional material on the death solidification process and its impact on the quality of products for salmon and cod producers in Iceland, which could benefit them in the future in tackling new challenges in the production of high-quality products.