Impact of dietary oil source on product quality of farmed Atlantic cod, Gadus morhua

Farmed Atlantic cod (Gadus morhua L) averaging 2 kg were fed extruded dry feed added either fish oil or soybean oil (total replacement) from August to October 2004. Thereafter all fish were fed the fish oil based diet from October to December. Analyses performed every second week showed that 18:2n-6 increased linearly in cod fed soybean oil (SO-group), while 20:1n-9 and 20:5n-3 decreased. The incorporation rate of 18:2n-6 was higher than dilution. Analyses revealed that 18:2n-6 was incorporated in phospholipids (PL) whereas the accumulation in triacylglycerols (TG) was less pronounced (p = 0.13). The 18:2n-6 also appeared in significant amounts in the FFA. Lipid class composition in fresh muscle was similar for cod fed the SO diet and FO diet: PL: 72-78%, TG: 5-9%, FFA: 17-19%. The content of FFA increased after long-term frozen storage whereas the PL decreased correspondingly. The SO-group had higher content of FFA and lower content of TG after 6 months of frozen storage, and the same tendency was seen after one year. Statistical analyses revealed significant interactions between frozen storage and dietary treatment for 18:1n-9, 20:5n-3 and 22:6n-3 in the PL, and for the 22:6n-3 in the FFA fraction. Dietary treatment had no significant impact on the cholesterol content in the muscle, and only traces of phytosterols were detected. Tougher texture, more gaping and higher liquid losses were observed after frozen storage irrespective of diet. The SO-group had less gaping after frozen storage, otherwise no significant dietary effects were observed. Consumers could distinguish the taste between the fish groups, but there was no overall preference for one type over the other. Replacement of fish oil by soybean oil in diets for Atlantic cod significantly altered the fatty acid profile, and also influenced changes in fatty acid composition upon frozen storage. No negative effects on texture, fillet gaping or liquid holding capacity were observed.