Physicochemical Changes in Rainbow Trout (Oncorhynchus Mykiss) after Freezing

Abstract

The aim of this study was to compare some physicochemical changes in the dorsal and ventral muscles of rainbow trout (Oncorhynchus mykiss) after freezing. A total of 45 fish were divided into three experimental groups. The first group consisted of fresh fish (n=15) while the second group encompassed frozen fish at – 18 °C for 15 days (n=15). The third group contained double frozen fish which were frozen at – 18 °C for 15 days, thawed, and frozen again under the same conditions (n=15). Water content, water activity, ash content, crude protein, and fat content were determined. There was a significant difference (р<0.05) between the water content of the dorsal muscle of the fresh fish (76.08%) and the double frozen fish (73.22%). Water activity differed substantially (р<0.05) in the dorsal (0.975) and ventral (0.960) muscles of the frozen trout, while it was significantly higher (р<0.05) in the dorsal muscle of the frozen (0.975) than the double frozen fish (0.967). Significant differences (р<0.05) in crude protein content were measured between the ventral muscle of the fresh (19.27%) and frozen fish (20.11%), as well as between the frozen (20.11%) and double frozen fish (19.29%). The fat content was significantly higher (р<0.05) in the ventral muscle (5.02%) than the dorsal muscle (3.83%) of the double frozen fish. It was concluded that freezing and storage at low temperatures affect the water content, water activity, crude protein, and fat content of rainbow trout (Oncorhynchus mykiss).