Evaluation of different vitamin E recommendations and bioactivity of α-tocopherol isomers in broiler nutrition by measuring oxidative stress in vivo and the oxidative stability of meat.

The aim of this study was to compare recommendations for vitamin E supplementation regarding high polyunsaturated fatty acid intake and to compare the bioactivity of RRR- and all-rac-α-tocopherol with respect to oxidative stress in vivo and the oxidative stability of broiler meat. Fifty male broilers were divided into 5 groups. All groups received diets with a high inclusion of fat (7.5%), one with palm fat and the others with linseed oil, which were either unsupplemented or supplemented with vitamin E to contain in total 85 or 200 IU of vitamin E as all-rac-α-tocopherol and 85 IU as RRR-α-tocopherol. Oxidative stress in vivo was studied by measuring the DNA damage; measuring malondialdehyde (MDA) in plasma, liver, and breast muscle; and analyzing the antioxidant capacity of the lipid-soluble compounds, total antioxidant status of plasma, and antioxidant enzyme assays. The tocopherols in plasma, liver, and breast muscle were also analyzed. In vitro oxidative stability was studied by measuring MDA in fresh, stored, and heat-treated breast meat. Linseed oil, as opposed to palm fat, induced DNA fragmentation and MDA formation. Both forms and concentrations of vitamin E reduced DNA damage and breast muscle MDA. The groups receiving 200 IU of all-rac-α-tocopherol and 85 IU of RRR-α-tocopherol had much higher values for antioxidant capacity of lipid-soluble compounds than did the controls. No differences were observed in the values of antioxidant enzymes. The α-tocopherol levels in tissues and plasma were significantly influenced by the level of α-tocopherol supplementation. Malondialdehyde formation in meat from the vitamin E-supplemented groups was decreased in comparison with that from the control linseed oil group. We conclude that both vitamin E concentrations were insufficient to prevent all harmful effects of lipid oxidation in vivo and that both were equally effective. On the contrary, to ensure good stability of meat lipids, higher vitamin E supplementation is needed, especially after heat treatment. The results of in vivo oxidative stress and meat lipid oxidation confirmed the currently accepted bioactivity of the RRR-α- to all-rac-α-tocopherol ratio of 1.39 in in vivo and in vitro systems.