Dietary macroalgae is a natural and effective tool to fortify gilthead seabream fillets with iodine: Effects on growth, sensory quality and nutritional value

Marine fish are a rich source of iodine in the human diet. Exogenous feeding under captivity opens the possibility of tailoring fish composition with health valuable nutrients, such as iodine, and establishing it as a functional food. A study was undertaken to test the efficacy of various dietary iodine supplemental forms on the growth performance of gilthead seabream and assess the effects on sensory attributes and nutritional value of fillets. Duplicate groups of 35 seabream (IBW: 252g) were fed over 118days: a) control diet (CTRL) with 3mgIkg−1, supplied as potassium iodide; b) this same control diet supplemented with potassium iodide (diet KI: 26mgI·kg−1) or with ethylenediamine dihydroiodide (diet EDDI; 22mgI·kg−1); c) a fourth diet with 10% of Laminaria digitata, an iodine-rich macroalgae (diet LAM). At the end of the trial, fish doubled their initial weight, but irrespective of the iodine form used, the elevation of dietary iodine level had no effect (P>0.05) on feed intake, growth rate, feed conversion, nutrient utilization or whole-body composition. Dietary iodine supplementation led to a significant increase (P<0.05) of the iodine content in seabream fillets. In comparison to the CTRL treatment (0.13mg·kg−1), seabream fed KI and EDDI supplemented diets showed a significant enhancement (P<0.05) of their fillet iodine content (0.17mg·kg−1). Feeding seabream with the iodine-rich brown algae L. digitata resulted in a significant (P<0.05) 6.5-fold increase (0.84mg·kg−1 fillet) of fillet iodine content over the levels found in the CTRL treatment. Overall sensory difference between CTRL and fish fed supplemented diets was significant (P<0.05) only for fish fed the EDDI diet. Steam-cooking elicited 13–20% losses of the iodine content of seabream fillets. Iodine supplementation had no effect (P>0.05) on the fatty acid profile of seabream muscle. Dietary iodine-rich macroalgae was an effective and natural strategy to fortify muscle with iodine, showing that a 160g portion of steam-cooked seabream fillets could cover approximately 80% of the Daily Recommended Intake for iodine and 370% of the Daily Adequate Intake of EPA+DHA for enhanced cardiovascular health in adults.