Protection of fish feed, made directly from marine raw materials, with natural antioxidants

The present experiments were designed to study the effects of different natural antioxidants in an experimental fish feed, made directly from marine raw materials. A rosemary extract (Herbalox®) and crystalline ascorbic acid were the most effective antioxidants in this feed and the effect of ascorbic acid was enhanced by adding a tocopherol mix. Ascorbyl palmitate, citric acid, a phosphate mix designed to enhance the effect of ascorbic acid, and spermine had minor antioxidant effects, no effect or pro-oxidant effects. It was necessary to add higher concentrations of the rosemary extract than the vitamin C/E combination to obtain an optimal antioxidant effect. A minor effect of adding ethoxyquin to a diet with tocopherol mix and ascorbic acid was detected in one of the experiments, but this effect was not reproduced in the other experiments. It is therefore concluded that the diet used in the present study can be protected against oxidation using natural antioxidants. Since antioxidants must be tested in the oxidising system in which they are going to be used, the present results have to be confirmed before applying them to commercial fish feeds and feed ingredients.