Rainbow trout (Salmo irideus) produced in Finland VI. Free amino acid composition of refrigerated and frozen rainbow trout

Changes in the amounts of free amino acids in rainbow trout during refrigerated storage in ice at + 4 . . + 6°C and in frozen storage at –18°C were investigated. The control sample was prepared directly from the killed, bleeded, and gutted fish. The results indicated that the total amounts of free aimino acids decreased in the refrigerated and in the frozen fish. These decreases depended mostly upon the steady decrease of the three quantitatively largest components, namely histidine, tryptophane, and glycine. Histidine formed 36.1 per cent, tryptophane 25.0 per cent, and glycine 15.1 per cent of the total amount of free amino acids in the control sample. In connection with many other amino acids a decrease in their amounts was noted during storage. Changes appearing in refrigerated fish were more distinct than in frozen fish.