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Sargassum fusiforme is a popular edible seaweed in coastal cities of China that contains diverse nutrients including iodine. Cooking is an effective way to improve food safety, but it can alter both the contents of elements along with speciation and bioavailability. Three common cooking methods, the soaking, steaming and boiling, were evaluated for their effects on the protein structures, protein digestibility, iodine content and iodine bioavailability of S. fusiforme.

Fourier transform infrared spectroscopy was used to study the structural changes of protein, and an in vitro digestion/Caco-2 cell culture system was used to evaluate the digestibility of protein, bioaccessibility and bioavailability of iodine.

Boiling and steaming altered the protein secondary structure demonstrated by increased a-helix and random coil and decreased β-sheet, which improved the in vitro protein digestibility. Iodine content was reduced by cooking, with the highest loss observed after boiling, followed by soaking and steaming, while it was found that both bioaccessibility and cellular uptake of iodine were significantly elevated by boiling and steaming using an in vitro digestion/Caco-2 cell culture system. The presence of ascorbic acid, citric acid or tyrosine was beneficial for the iodine absorption, while oxalic acid and phytic acid hindered the iodine bioavailability.

The present finding suggested that cooking was conducive to the digestion and absorption of iodine in S. fusiforme. In addition, different dietary factors could have a certain impact on the absorption of iodine. Results of the study are essential for improving the application value of S. fusiforme to ensure reasonable consumption of seaweeds.

Seaweeds are gaining broader interest in Western societies through their use in product development and the health-food industry. High nutritional value, low carbon footprint and sustainability are key drivers for seaweed uptake in Europe; yet high iodine intake from seaweed remains a concern. This study seeks to identify seaweed food products available on the UK retail market between 2018 and 2021 and assess their safety in the context of iodine exposure.

Here, a market survey (n = 37–40 retailers) was conducted in three annual waves to evaluate seaweed food product availability in the UK. The iodine dose of products was estimated based on a comprehensive literature review of seaweed iodine content.

This study shows a young, dynamic market with 2.3-fold increase in seaweed food product availability since the last available published data (2015). Specific iodine content labelling remains uncommon, and median iodine doses in a single serving of food exceeded 400 µg in all years. Some products, especially seaweed supplements, provide iodine doses above the tolerable upper limit and upper level of tolerance.

This study presents the most contemporary and comprehensive overview of the market for seaweed food products in the UK. With increasing popularisation of seaweed as a food, this study highlights the need for improved dialogue amongst producers, retailers, legislators and public health specialists to address the risk of iodine excess, and the concurrent scope for processing methods to reduce the iodine content in seaweeds.