Mustafa YILDIZ, Hüseyin GÜN, Erdal ŞENER

Effect of refrigerated storage on fillet lipid quality of rainbow trout (Oncorhynchus mykiss W.) fed a diet containing different levels of DL $alpha$ -tocopherol acetate

Antioksidant madde olarak artan düzeylerde (sırasıyla 100, 300 ve 500 mg $kg^{-1}$ diyet) $alpha$ -tocopherol acetate ilave edilen diyetlerle beslenen üç grup gökkuşağı alabalığının filetolarındaki E vitamini düzeyine, yağ asidi kompozisyonuna ve lipit oksidasyonuna 1 ± 0,3 °C ' de yapılan soğuk depolamanın etkisi incelendi. 58 gün süresince deney diyetleri ile beslenen balıklar (ortalama başlangıç ağırlığı, 131 ± 1,0 g) deney sonunda ortalama olarak 299 ± 6,1 g ağırlığa ulaştı ve deney grupları arasındaki istatistiki fark önemsiz bulundu (P > 0,05). Balıkların fileto örnekleri taze (0. gün) ve 9 gün süresince 1 ± 0,3 °C 'de yapılan depolamadan sonra analiz edildi. Filetolardaki yağlarda meydana gelen oksidasyonu ölçmek amacıyla tiyobarbutirik asit reaktif (TBARS) testi kullanılmıştır. 58 günlük yemlemenin sonunda diyetlerdeki E vitamini düzeylerinin balıkların filetosundaki $alpha$ -tocopherol ve TBARS düzeylerini önemli derecede etkilediği görülmüştür. Deney sonunda E100, E300 ve E500 diyetleri ile beslenen balıkların filetolarındaki $alpha$ -tocopherol düzeyleri sırasıyla 30,1 ± 0,2, 34,3 ± 0,1 ve 40,1 ± 0,1 mg $kg^{-1}$ olarak bulunmuş ve bu oranlar 9 gün süresince 1 ± 0,3 °C 'de yapılan depolamada giderek azalmıştır (P < 0,05). Buna karşın, yemleme deneylerinin sonunda balıkların filetosundaki TBARS değerleri sırasıyla 4,4 ± 0,1, 4,2 ± 0,0 ve 2,2 ± 0,0 mg malondialdehyde (MDA) $kg^{-1}$ olarak bulunmuş ve 9 gün süresince 1 ± 0,3 °C 'de yapılan soğuk depolamada TBARS değerleri giderek azalmıştır (P < 0,05). Diyetteki E vitamini düzeyleri balık filetolarındaki yağ asidi kompozisyonunu etkilememiştir (P > 0,05). Ancak soğuk depolama sırasında toplam doymuş yağ asitlerinin (SFA) konsantrasyonu giderek artmış ve toplam çok doymamış yağ asitlerinden PUFA'ların konsantrasyonu giderek azalmıştır (P < 0,05). Sonuç olarak 130 mg $kg^{-1}$ 'dan 580 mg $kg^{-1}$ 'a doğru artan düzeylerde $alpha$ -tocopherol acetate içeren diyetlerle beslenen balıkların filetoları 9 gün süresince 1 ± 0,3 °C 'de depolanmış ve diyetlerde artan $alpha$ -tocopherol acetate miktarlarına karşın filetolardaki lipit oksidasyonunun azaldığı görülmüştür.

Farklı düzeylerde DL $alpha$ -tocopherol acetate içeren diyet ile beslenen gökkuşağı alabalığı (Oncorhynchus mykiss W.)'nın fileto lipit kalitesine soğuk depolamanın etkisi

The effect of refrigerated storage at 1 ± 0.3 °C 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 °C 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 E100, E300 and E500 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 °C (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 °C (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 °C.

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