Iodine reduction and retention of nutrients and flavour-active compounds upon warm seawater treatment of the kelps Alaria esculenta and Saccharina latissima

Abstract

Commercially cultivated kelp (seaweed) species represent a potential dietary source of iodine but may also put consumers at risk of excessive intakes upon frequent consumption. This study investigated warm seawater (W-SW) treatment as a simple method for reducing the iodine content of Alaria esculenta and Saccharina latissima. Iodine concentrations decreased in both kelps upon W-SW exposure at 45 °C, i.e. by 38 % and 78 %, respectively, in A. esculenta and S. latissima after 1 min and 51 % and 88 % after 2 min. Longer treatments resulted in further decrease in A. esculenta whereas only marginal further reduction in iodine concentrations were achieved in S. latissima. No reduction in iodine concentration was measured in S. latissima following treatment at 35 °C (not tested for A. esculenta). W-SW treatment at 45 °C induced loss of biomass in both kelps although the total retention was notably higher in A. esculenta compared to S. latissima. Among the analysed macronutrients, potassium and mannitol were associated with the lowest retentions. Losses of micronutrients (incl. vitamin B1 and B9) and trace elements were also measured in both kelps. The retention of free glutamate was high in both species suggesting that W-SW exposure does not negatively affect the umami potential of the final ingredients for food. Based on portions contributing 600 μg iodine, W-SW-treated A. esculenta was more nutritious than a comparable ingredient from S. latissima, with nutritionally relevant contribution (> 15 % of dietary reference intake (DRI)) per portion (4.6 g dry A. esculenta vs. 1.2 g S. latissima) of sodium, and notable contributions (> 5 % of DRI) of other minerals (calcium, magnesium and potassium) and vitamin B9. Short W-SW treatment is a simple approach that could be implemented in commercial kelp production and contribute to reducing the risk of excessive dietary iodine exposure from seaweed consumption.