Effect of Refrigerated Storage on Fillet Lipid Quality of Rainbow Trout (Oncorhynchus mykiss W.) Fed a Diet Containing Different Levels of DL a-Tocopherol Acetate

Authors: MUSTAFA YILDIZ, ERDAL ŞENER, HÜSEYİN GÜN

Abstract: The effect of refrigerated storage at 1 ± 0.3 ºC on vitamin E level, fatty acid composition and lipid oxidation of fillets was studied in 3 groups of rainbow trout fed diets supplemented with increasing levels (100, 300 and 500 mg kg^{-1} diet, respectively) of \alpha-tocopherol acetate as antioxidant. Fish (initial mean weight 131 ± 1.0 g) were fed experimental diets for 58 days and reached a mean final weight of 299 ± 6.1 g, with growth differences among the 3 experimental groups being insignificant (P > 0.05). Fillet samples of fish were analyzed fresh (on day 0) or after storage at 1 ± 0.3 ºC for 9 days. Lipid oxidation was measured using the thiobarbituric acid reactive substances (TBARS) test. Dietary vitamin E levels had a significant effect on fillet \alpha-tocopherol levels and TBARS values of fish by the end of 58 days of feeding. At the end of the feeding trial the fillet \alpha-tocopherol levels of fish fed E_{100}, E_{300} and E_{500} diets were 30.1 ± 0.2, 34.3 ± 0.1 and 40.1 ± 0.1 mg kg^{-1}, respectively, and the fillet \alpha-tocopherol levels were gradually decreased during the 9 days of storage at 1 ± 0.3 ºC (P < 0.05). However, at the end of the feeding trial the fillet TBARS values of fish fed diets were 4.4 ± 0.1, 4.2 ± 0.0 and 2.2 ± 0.0 mg malondialdehyde (MDA) kg^{-1}, respectively, and the fillet TBARS values gradually increased during the 9 days of storage at 1 ± 0.3 ºC (P < 0.05). Dietary vitamin E levels did not influence the fatty acid composition of the fish fillets (P > 0.05). However, during the refrigerated storage period, total saturated fatty acid (SFA) concentration slowly increased and total polyunsaturated fatty acid (PUFA) concentration slowly decreased (P < 0.05). Finally, increasing the levels of \alpha-tocopherol acetate in the diets from 130 to 580 mg kg^{-1} can slow down the level of lipid oxidation in fish fillets during refrigerated storage for 9 days at 1 ± 0.3 ºC.

Keywords: Rainbow trout, nutrition, \alpha-tocopherol acetate, fillet, refrigerated storage, lipid oxidation

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