Quantification of iodine loss in edible Irish seaweeds during processing

Exposure to seaweed-derived iodine through the consumption of macroalgae can positively and negatively influence human health, depending on whether adequate (150 mu g day(-1)) or excessive quantities are ingested. Following harvest, macroalgal material typically undergoes certain processing procedures involving washing, dehydration, rehydration (soaking) and cooking (boiling) before it is consumed. In this study, we assessed iodine in edible brown (Alaria esculenta), red (Palmaria palmata) and green (Ulva intestinalis) macroalgae and quantified the iodine loss during processing. Freshly collected A. esculenta contained higher quantities of iodine (670 mu g (g dw)(-1)) than P. palmata (97 mu g (g dw)(-1)) and U. intestinalis (92 mu g (g dw)(-1)), implying that only 0.2-1.6 g dw of freshly harvested algae contain the recommended daily intake level. Washing (10 min in deionised water) and dehydration (air-, oven- and freeze-drying) at low irradiances only marginally affected iodine levels, suggesting that gentle preservation techniques prevent iodine loss. By contrast, rehydration (1-24 h soaking in deionised water) significantly reduced iodine: by 62 % in A. esculenta, by 15 % in P. palmata and by 10 % in U. intestinalis. The iodine levels of all three species decreased further upon boiling (20 min in deionised water). Despite a considerable, but species-specific, loss of iodine during processing, all macroalgae still contained iodine at 66 to 165 mu g (g dw)(-1) after rehydration and subsequent boiling. Our results indicate that both raw and processed macroalgae can be considered as a rich source of iodine and thus their consumption may influence human health and nutrition.