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Astaxanthin in juvenile farmed Chinook salmon (Oncorhynchus tshawytscha) : effective dietary levels for flesh pigmentation and influence on fatty acid profile during cold temperature storage of fillets Thomas, Alison Carolyn

Abstract

Astaxanthin (Ax) is the pigment responsible for the characteristic flesh colour of salmonids and must be present in the diet of farmed salmon in order for them to attain a colour acceptable to consumers. These studies were conducted to investigate the potential for early pigmentation in chinook salmon, to determine an effective dietary concentration of Ax for juvenile chinook, and to examine possible antioxidative activity of Ax in salmon fillets stored under aerobic and anaerobic conditions at -3°C. In Experiment 1, all-female chinook salmon smolts with a mean initial body weight of ~40g were fed a diet containing no added Ax (control), or one of three diets containing low (3 mm pellet, 29.56 ppm Ax; 4 mm pellet, 25.73 ppm Ax), medium (3 mm pellet, 40.11 ppm Ax; 4 mm pellet, 39.60 ppm Ax) or high (3 mm pellet, 76.42 ppm Ax; 4 mm pellet, 59.82 ppm Ax) synthetic Ax. Fish were fed the 3 mm pellet for the first three monihs and the 4 mm pellet for the remainder of the study. At three and seven months, 24 fish per treatment were sacrificed and analyzed for colour using the Roche Colour Card for Salmonids, a Hunter Lab Labscan, and quantification of flesh Ax concentrations by high performance liquid chromatography. Results from Experiment 1 showed that chinook salmon weighing < 120 g were capable of attaining a high degree of visible pigmentation. In general, there was not a good direct relationship between fish size and flesh level of Ax. The concentration of Ax in the diet had a significant effect on flesh colour and Ax content, but not the proximate composition of the fillet. Time was not a significant factor in pigmentation, however the time*diet interaction was significant. Good correlations (r > 0.8) were found between flesh levels of Ax and the Hunter Lab a, chroma, and Roche Colour Card scores. In Experiment 2, pigmented and non-pigmented fillets were stored at -3°C for up to 6 weeks under aerobic and anaerobic conditions. Methyl esterified lipid extracts from all fillets were analyzed via gas chromatography to assess changes in fatty acid composition attributed to oxidation. Analysis of the ratios of unsaturated to saturated fatty acids and polyunsaturated to saturated fatty acids from Experiment 2 revealed no significant difference due to pigmentation of fillets. This indicates that astaxanthin had neither antioxidative nor prooxidative activity under the conditions used in the present study.

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