Relevance of dietary oil source for contraction and quality of pre-rigor filleted Atlantic cod, Gadus morhua

Rigor contraction and quality development were studied during storage of pre-rigor fillets of farmed Atlantic cod (body weight 2 kg). For eight weeks prior to slaughtering, the fish were fed diets containing either 100% fish oil (M-group) or 60% fish oil and 40% soybean oil (S-group). Filleting was performed 0.5 h after slaughtering and the fillets were stored at 6 °C for 48 h post-mortem. The contraction rate was faster for the S-group, but after 48 h storage the contraction was 21% of the initial fillet length for both fish groups. The ATP content analysed 1 h post-mortem was lower of the S-group (4.5 μm g− 1 ww) compared with the M-group (6.1 μm g− 1 ww). After 16 h, the ATP content was similar for both fish groups (1.7–2.2 μm g− 1 ww). The muscle pH analysed 1 h post-mortem was 0.2 unit lower of the S-group (pH 6.9) than of the M-group (pH 7.1). From 8 to 12 h, the pH fell significantly to 6.3 and 6.6 for the S-group and M-group, respectively. From 24 h and onwards, the pH was similar of both fish groups (pH 6.2). Texture development differed significantly due to dietary treatment. The S-group had highest initial breaking force, demonstrating that the texture of this group was firmer immediately after slaughtering. The breaking force of the S-group dropped to a stable level after 4 h, whereas the breaking force of the M-group decreased continuously during the storage period. The breaking force was similar of both groups after 16 h storage. The L*-value (lightness) increased during the first 4–6 h storage. From 8 to 16 h, the L*-value was stable or slightly decreasing. The L*-value was consistently higher of the M-group. In conclusion, dietary inclusion of soybean oil resulted in faster energy depletion post-mortem, faster rigor contraction, faster reduction of the breaking strength and lower L*-values.