Seaweed storage: a not so insignificant stage for iodine content

Seaweed is a very important source of iodine. Iodine is an essential trace element, vital for the body and for the proper functioning of the thyroid gland. Iodine is recognised for its many functional properties, including its contribution to energy metabolism, the maintenance of intellectual and nervous functions and the normal health of our skin.

Among seaweeds, Saccharina latissima has an exceptional iodine content, averaging 4100 mg/kg (CEVA database), which can sometimes have an impact on its marketing. In France, ANSES recommends a maximum value of 2000 mg/kg DM (referral 2017-SA-0086) for seaweed intended for human consumption. As a result, traditional bleaching processes are recommended after harvesting to reduce iodine content.

In this study, the algae were pre-stored for 3 days under different conditions to induce a stress reaction and thus potentially reduce the iodine content:

  • high or low light conditions
  • low or high seawater renewal

The iodine content of algae stored in tanks with low light intensity and low water renewal appears to be reduced (2100 mg.kg-1 ±700 mg.kg-1). However, the difference is not significant with freshly harvested algae given the high variability of raw algae (3300 mg.kg-1 ±1400 mg.kg-1).

The authors expected a significant reduction in iodine content due to stress during storage.
However, after the bleaching step, the authors found a significant difference between stored and unstored algae. Bleaching was carried out at 90°C for 2 min in fresh water.

Seaweed stored in tanks showed an 87% reduction in iodine content, whereas the reduction for unstored seaweed was 80%. Although this difference is small, the authors conclude that there is an additional effect of the storage stage prior to bleaching.

To explain this effect of storage, the authors put forward 3 hypotheses:

  • modification of the speciation of iodine: the period of stress linked to storage would generate an increase in the relative content of mineral iodine (more ‘leachable’ iodine)
  • modification of the intermediate storage of iodine in the cell: passage from internal iodine to more external tissues
  • modification of the regulation of enzymes linked to iodine fluxes

Future experiments are needed to confirm these initial results and explain this effect of intermediate storage. Optimising storage to obtain the lowest possible iodine content in Saccharina latisisima is an interesting option for the large-scale use of the alga by food manufacturers.

CEVA’s opinion

In this study, we observed a cumulative effect of soaking (storage under low water renewal) and bleaching on the reduction of iodine content. This is an interesting result for iodine reduction strategies in brown seaweed.

Reference: Blikra, Marthe Jordbrekk; Skipnes, Dagbjørn (2024) Live storage of kelp under stressful conditions led to higher iodine reductions during subsequent blanching. In : Journal of Applied Phycology. DOI: 10.1007/s10811-024-03204-2 .

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