Super freezing of fish
Special Symposium - Innovations in Food Technology (LMC Congress)
Innovations in Food Technology - Poster Session (Food - P2)
Keywords: freezing, fish
Freezing of fish is an effective way of long term preservation and it has been shown that fish stored for up to three month under ideal conditions cannot be distinguished from fresh fish regarding colour, taste and texture. However, little is known, about the relation between loss of quality, storage time and storage temperature in the interval between -10 and -80 °C. Also, little is known about to which degree different quality deteriorating processes occur at the different temperatures. One of the main purposes of this study is to investigate this relation as well as explaining which physical and biochemical processes that lead to loss of quality during frozen storage of fish.
An experimental design was set up with eight different storage temperatures from -10 to
-80 °C (10 °C intervals) and 11 storage periods (1, 2, 3, 4, 5, 6, 8, 10, 12, 15, and 18 months respectively). Cod and salmon were used as model fish representing lean and fat fish species, respectively. Sixteen cod and sixteen salmon were filleted and the middle part of each fillet cut in four pieces and quickly frozen in a -40 °C blast freezer. Afterwards the eight pieces were randomly assigned to the different temperatures. In order to avoid influence of diversity between individuals when investigating the effect of different storage temperatures, the experiments were paired regarding temperature, so that pieces stored for a given number of month at the eight different temperatures originated from the same fish. For each storage period two different fish (two cod and two salmon) were examined using the following analyses: water holding capacity, fluorescence spectroscopy, nuclear magnetic resonance spectroscopy, determination of thiobarbituric acid-reactive substanses and carbonyl groups, and activity of the enzymes Sarcoplasmic Reticulum Ca2+-ATPase, cathepsin D and metallo-proteases. These different analyses provide information about the degree of protein oxidation, protein denaturation and lipid oxidation and the water distribution in the fish muscle. The results will be analysed using multivariate data analysis.
It is expected that the quality of the fish declines the longer the storage time and the higher the temperature. The analyses mentioned should provide information about whether the loss of quality is a continuous or stepwise function of temperature at the various storage times. Ideally the experiment will make it possible to determine an optimal temperature for frozen storage of lean and fat fish.
