EFFECT OF DIETARY VITAMIN-E SUPPLEMENTATION IN TROUT ON LIPID-PEROXIDATION IN FILLETS DURING FROZEN STORAGE

Rainbow trouts were fed a complete diet with 12 mg vitamin K-3 and supplemented with 20, 200 or 2 000 mg all-rac-alpha-tocopheryl-acetate/kg for 18 weeks. The ratio of the vitamin E-sup-plementation was 1 : 10 : 100. Fillets were minced and stored at -18 degrees C. Concentrations of alpha-tocopherol and phylloquinone and parameters of lipid peroxidation were measured after 4, 6, and 8 months of storage. The effects of alpha-tocopherol incorporated into fillets on storage stability were assessed by measuring free fatty acids, peroxides, malondialdehyde and lipofuscin. Mean alpha-tocopherol-concentrations in fillets were 1.4, 2.7 and 16.3 mg/100 g, respectively representing ratios of 1 : 2 : 12. The increase in alpha-tocopherol concentration resulted in a significant improvement of storage stability. The phylloquinone concentration in fillet was reduced in treatments with greater than or equal to 200 mg vitamin E/kg; however, this did not affect the prothrombin time. No peroxides were detectable at any time. The concentrations of malondialdehyde significantly decreased with increasing supplementation of vitamin E. Lipofuscin concentrations were higher with low than with high vitamin E supplementation. The dose-related inhibition of lipid peroxidation became apparent in decreased concentrations of free fatty acids in the crude fat. These results confirm the effectiveness of alpha-tocopherol as antioxidant in fish flesh. In this study the incorporation of alpha-tocopherol from dietary supplementation improved the long-term storage quality of trout fillets due to the effective inhibition of the lipid peroxidation. A measurable improvement of the storage stability was achieved with a supplementation of 200 mg vitamin E/kg feed.