Flesh Lipid and Carotenoid Composition of Scottish Farmed Atlantic Salmon (Salmo salar)

Abstract

Samples of steaks from market-size salmon (2.5-5 kg), produced under the requirements of the Product Certification Scheme for Scottish Quality Farmed Salmon, were obtained from five Scottish salmon producers on a weekly basis for over 2 years. Samples were assayed for total lipid content, lipid class composition, fatty acid composition, vitamin E content, and carotenoid pigment [astaxanthin (AX) and canthaxanthin (CX)] content. In addition, samples were obtained from the same producers to assess loss of carotenoid pigment in the period up to 120 h post-harvest and to measure lipid and pigment content of different body regions. The analyses showed a positive correlation between dietary lipid and deposition of lipid in flesh, although there was great variation in flesh lipid content within each dietary lipid level. The average lipid content of Scottish salmon was 10.1 +/- 2.9% (n = 495). Salmon flesh was rich in the n-3 highly unsaturated fatty acids, 22:6n-3 and 20:5n-3, with average values of 11.3 and 5.4% of total fatty acids or 10.2 and 4.8 g/kg flesh, respectively. Vitamin E content of salmon flesh was around 30 mg/kg but was significantly higher in fish fed the lowest dietary lipid level. Studies investigating changes in carotenoid pigmentation up to 120 h post-harvest suggested that fish fed AX alone showed a loss of pigment over time that did not occur in fish fed either CX alone or a combination of AX and CX. Measurement of lipid content of different body regions showed that the highest levels were found in the region immediately in front of the dorsal fin and that the lowest lipid levels were in the tail region. Total lipid content of all five body zones was positively correlated with dietary lipid. Carotenoid pigment levels were the same across all body zones and were not affected by dietary lipid.

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“…This has also been observed in marine carnivorous species such as red sea bream, Pagrus major (Huang et al, 2007); turbot, Psetta maxima (Bell et al, 1994;Regost et al, 2003) and European sea bass (Mourente et al, 2005a). Accordingly, in the present study some fillet fatty acid concentrations were very closely correlated with dietary fatty acid concentrations, recording R 2 values higher than 0.8 (such as 14:0, 18:2n-6, 20:5n-3 and 22:6n-3), as previously reported (Bell et al, 1998;Bell et al, 2001;Bell et al, 2002). This observation is particularly important for the two main n-3 LC-PUFA (namely 20:5n-3 -EPA-and 22:6n-3 -DHA), as they are responsible for the renown health benefit of eating fish, and are clearly important in determining the overall nutritional quality of aquaculture products.…”

Development of Lipid Changes Related to Quality Loss During the Frozen Storage of Farmed Coho Salmon (Oncorhynchus kisutch)

“…The content of such compounds provided some differences throughout the experiment that could be explained as a result of differences from fish to fish and not as a result of the frozen storage. Both isomers (alpha and gamma) showed similar results to those obtained when studying other cultivated fish species such as rainbow trout [34] and Atlantic salmon [35]. In the present experiment, both tocopherol isomers did not decrease significantly (p > 0.05) with the storage time, although previous research indicates important losses in both isomers during the frozen storage of other farmed species such as blue and red tilapia [36] and channel catfish [37].…”

Metabolism and Functions of Lipids and Fatty Acids in Teleost Fish

“…Thus, selective oxidation of saturated and monounsaturated fatty acids, and perhaps also 20:5n-3, by swimming muscles leading to the selective retention of 22:6n-3 may be a more general feature of fish (see section 4.1.2 below). Consistent with this, the ratio of 22:6n-3 : 20:5n-3 is consistently higher in the lipids deposited in the flesh of farmed Atlantic salmon compared with the fish oils currently used in salmon feeds (Brodtkorb et al, 1997;Bell et al, 1998).…”