TEXTURE PROPERTIES OF FARMED RAINBOW-TROUT (ONCORHYNCHUS-MYKISS) - EFFECTS OF DIET, MUSCLE FAT-CONTENT AND TIME OF STORAGE ON ICE

Groups of rainbow trout (Oncorhynchus mykiss) fed diets with low or hi gh fat content were stored on ice for up to 11 days in two separate ex periments. After 4, 9 and 11 days storage on ice in the first experime nt and after 5, 8 and 11 days in the second experiment the fish were f illeted by hand and fillet gaping was evaluated. Texture properties we re studied using an Instron compression test. pH was measured in all f illets. In fillets from the second experiment, also fat content and au tolytic protease activity were measured. Diet affected fillet fat cont ent and texture properties. Fish fed high fat diet exerted less resist ance against compression, indicating a softer consistency. Force at yi eld point and slope were not significantly affected by diet. The high fat group had higher autolytic protease activity than the low fat grou p. The results from the Instron measurements indicated that the fish b ecame softer and less tough during 11 days storage on ice. A slight, b ut statistically significant increase in pH with time was observed in both experiments. In the first experiment a reduction in gaping scores was observed during storage, as opposed to a significant increase in the second experiment. The texture parameters yield point and slope we re negatively correlated to gaping in the second experiment.