Challenges of the usage of ultra-low temperatures for fish freezing and storage.

The physical states of frozen fish (muscles and oils) was analysed in the temperature range between -150.0 and 20.0 °C. The information of the glass transition temperature, the end of freezing point, the amount of unfrozen water, the amount of liquid fraction of oil was obtained by the method of Differential Scanning Calorimetry (DSC). Five commercial fish species were investigated: Atlantic Cod, Atlantic Herring, Atlantic mackerel, Atlantic salmon and rainbow trout. The glass transition was detected in the temperature range between -84.2 °C and -6.7 °C in fin muscles. The amount of unfreezable water was calculated in the range between 5.1 and 8.6 %. A significant fraction of fish oil (between 40.0 and 60.0) remained unfrozen at ultra-low temperatures. The packaging materials with medium barrier properties were considered to be of a great importance for the long-term storage of fatty fish due to a high amount of liquid fats at these temperatures. The two temperatures provided the high quality storage were proposed: below -35 °C and below -86 °C.