Color 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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Effect of high pressure processing in reducing Listeria spp. and on the textural and microstructural properties of cold smoked salmon (CSS)

Post author By admin
Post date 01/08/2007

Published:

01/08/2007

Authors:

Hannes Hafsteinsson, Ásbjörn Jónsson, Valur Norðri Gunnlaugsson, Birna Guðbjörnsdóttir, Magnús Guðmundsson

Supported by:

Icelandic Research Center Research Fund

Contact

Valur Norðri Gunnlaugsson

Research Group Leader

valur.n.gunnlaugsson@matis.is

Effect of high pressure processing in reducing Listeria spp. and on the textural and microstructural properties of cold smoked salmon (CSS)

The main objective of the project was to investigate the effect of hypertension (400-900 MPa) on the death of the bacterium Listeria monocytogenes and quality factors (image structure, texture and color) in cold smoked salmon after treatment for 10, 20, 30 and 60 seconds. Effects on the total number of aerobic bacteria, lactic acid bacteria and Bacillus spores were also studied. Two experiments were performed, one in July 2005 and the other in November 2006. The study showed that short-term hypertension treatment was effective in improving the quality and safety of cold-smoked products. Due to changes in the appearance and texture of the products, further research is needed. This new method promises to meet the requirements for longer shelf life of smoked salmon. The study is of great value to the industry, due to the innovation of using high pressure for a short time (seconds) to eliminate the bacterium Listeria in smoked salmon and thus increase the shelf life of this valuable product.

The main object of this research was to study the effects of high pressure processing (400-900 MPa) on the survival of Listeria monocytogenes and the characteristics (microstructure, texture and color) of cold smoked salmon when it was processed for 10, 20, 30 and 60 seconds. The changes in counts of total aerobic bacteria, lactic acid bacteria and Bacillus spores were also studied. Two experiments were carried out, one in July 2005 and the second in November 2006. It is concluded here that the combination of high pressure and short time treatment is very effective to improve the quality and safety of cold smoked products. However, because of the changes in the visual appearance and texture, further studies are necessary. This new development is promising to meet requirements for extended shelf life of ready-to-eat cold smoked salmon with high microbiological quality and safety. This study is of high industrial relevance because it combines the innovative approach of using high pressure processing for short time (seconds) to reduce the number of Listeria in cold smoked salmon and thereby extend the shelf life of this valuable product.