Effect of oxidized dietary lipid on growth, muscle and liver quality of juvenile Atlantic cod (Gadus morhua), and the protective role of vitamin E

Zhong, Ying (2006) Effect of oxidized dietary lipid on growth, muscle and liver quality of juvenile Atlantic cod (Gadus morhua), and the protective role of vitamin E. Masters thesis, Memorial University of Newfoundland.

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Abstract

The effects of oxidized dietary lipid and the role of vitamin E on growth performance, health status, and muscle and liver quality of juvenile Atlantic cod (Gadus morhua) were evaluated over a 9-week feeding period. Four isonitrogenous experimental diets containing fresh or oxidized fish oil with or without added vitamin E (a-tocopherol or mixed tocopherols) were fed to juvenile cod in duplicate tanks. The highly oxidized lipid used had a peroxide value of 94 meq/kg oil. No significant change (P>0.05) on growth performance or feed utilization was observed when oxidized dietary lipid was used. The erythrocyte osmotic fragility (EOF), referred to as susceptibility to hemolysis, of fish fed oxidized oil without added vitamin E was high in comparison with those fed unoxidized oil. Supplementation of δ-tocopherol appeared to decrease the hemolysis, but mixed tocopherols had no significant effect (P>0.05) on EOF. The proximate composition of fish whole body was also affected by oxidized oil and vitamin E. Fatty acid composition of liver total lipid reflected that of dietary lipid. However, muscle lipid contained high levels of polyunsaturated fatty acids (PUFA) compared to that of liver lipid, as expected. Both muscle and liver fatty acid composition followed the same trend among the treatments as those of dietary fatty acids. Fish fed fresh oil had a higher proportion of polyunsaturated fatty acids (PUFA) in muscle and liver lipid than those fed oxidized oil. Fatty acid composition of neutral lipids and phospholipids in fish muscle tissue was also analyzed. A larger quantity of eicosapentaenoic acid (EPA) was present in neutral lipid fraction, while phospholipids contained a higher amount of docosahexaenoic acid (DHA). Oxidized oil significantly (P<0.05) decreased the deposition of α-tocopherol in liver but not in muscle. Gamma- and δ-tocopherols from dietary tocopherols mixture were retained at very low levels in liver but higher retention was observed in muscle. The oxidative state of both liver and muscle, as measured by the 2-thiobarbituric acid reactive substances (TBARS) and headspace propanal, negatively correlated with tissue vitamin E levels. It is suggested that oxidized oil affected juvenile Atlantic cod by causing vitamin E deficiency in certain tissues and that these effects could be alleviated by supplementation of a sufficient amount of vitamin E through diet. It is also indicated that mixed tocopherols were good antioxidants for Atlantic cod, although less effective than α-tocopherol alone in many tissues with the exception of muscle, where γ-. and δ-tocopherols were deposited at considerably high levels. Due to the fact that muscles are the major edible part of fish, these results may be useful to fish farmers for producing fish with better oxidative stability and hence extended shelf life during storage.

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