Various methods currently exist to reduce the iodine content of seaweed, especially those with high levels. However, the impact of these treatments on other nutritional compounds and on the flavour of the seaweed has not always been assessed. It is this aspect that is reported in the study presented below.

In recent years, methods have been developed to reduce the iodine content of kelp. While iodine intake is an undeniable nutritional asset, excessive consumption is not to be recommended. Treatments have therefore been developed for certain species that are particularly rich in iodine. Conventional methods of blanching in boiling water (fresh or sea water) and maceration in lukewarm water can reduce iodine content by up to 80%.

But what about the other components of interest, the aroma, the flavour of seaweed and the famous Umami sought after as a flavour enhancer? Aroma is one of the key factors in consumer acceptance of a new food, and it would be a shame to downgrade the flavour of seaweed. Compromises have to be made between health safety and flavour.

The authors of this study evaluated the effect of different pre-treatments on Saccharina latissima: rinsing in hot water at 45°C for 2 minutes (fresh or sea water) and steaming at 90-95°C for 20 minutes. The pre-treated seaweed is freeze-dried before being analysed for mineral content, specifically iodine, sodium, potassium, calcium and magnesium, fatty acid profile, protein content and heavy metals (As, Cd, Hg, Pb and Cu). A descriptive sensory analysis was carried out by a panel of experts trained on seaweed alone, and its aromatic contribution to a dehydrated spinach soup was also assessed (incorporated at 0.5 and 1%).

The pre-treatments carried out do result in a reduction in iodine content: from 25% (steaming) to 73%-90% for rinsing in fresh or sea water. The greatest reductions are obtained for the lowest algae/water ratio.

The type of water has an impact on the loss of other components, with a greater loss of soluble compounds for algae treated with fresh water, essentially minerals and carbohydrates. Seawater treatments have a lesser effect on total dry matter, although the mineral profile changes: sodium content increases and potassium content decreases.

The sensory profile reflects this change in minerals, with a saltier flavour in seaweed treated with seawater and a more intense umami flavour. Overall, the flavour of the freshwater-treated algae was weaker, indicating a significant loss of aromatic compounds. As a result, only the seaweed treated with seawater was used as an ingredient in a spinach soup. The panellists were able to differentiate between soups with and without 0.5 and 1% seaweed. At this stage, there was no descriptive analysis of the soup’s aromas. 5 out of 16 judges reported that the soup with seaweed seemed saltier. This needs to be considered in the future to reduce the salt content of the recipe to compensate for the addition of seaweed.

In conclusion, treatment with warm seawater (45°C) for a short time (2 min) may be an alternative method for reducing the iodine content of brown seaweed while limiting nutrient losses and maintaining the seaweed’s flavour and taste potential for incorporation into food products. To simplify the use of seawater for chefs or industrialists, it would also be interesting to assess the effect of a salt water treatment.

Krook, J.L., Duinker, A., Larssen, W.E. et al. Approaches for reducing the iodine content of the brown seaweed Saccharina latissima—effects on sensory properties. J Appl Phycol (2023).

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