Fillet texture and protease activities in different families of farmed Atlantic salmon (Salmo salar L.)

A total of 738 Atlantic salmon (Salmo salar L.) from 94 families were slaughtered, pre-rigor filleted, and stored on ice. Fillet texture was measured instrumentally at 2 and 5 days post-mortem. Significant differences in fillet texture were found between families both at 2 and 5 days, and the loss of fillet firmness between 2 and 5 days also varied significantly between families. Based on texture measured at 2 days post-mortem, 3 groups of 6 families with either an average soft, intermediate, or firm texture were chosen for cathepsin B and L activity measurements. Muscle cathepsin B and L activities at 2 days post-mortem were determined on 123 salmon, and significant differences were found between the 3 textural groups: there was a significant negative correlation between fillet firmness and level of cathepsin L activity. These results indicate a genetic variation in fillet firmness and muscle cathepsin activity and also a relation between high muscle cathepsin activity and muscle softening post-rigor. The calpain/calpastatin protease system was also investigated. Calpain (probably m-calpain) activity was measured on 57 salmon from 9 of the families (soft, intermediate, or firm texture, 3 families per textural group) at 2 days post-mortem. Although differences in calpain activity between textural groups of families were observed, calpain activity was not significantly correlated to fillet texture. Calpastatin was measured on 50 salmon from the same 9 families 2 days post-mortem, but no significant correlation to fillet texture was detected. A tendency to higher calpastatin activity in the firm family group, however, suggests that the possible role of the calpain/calpastatin system in salmon fillet texture needs further investigations. No gender differences were observed in any of the traits investigated.