10.3.5.1 Iodine

Marine algae are known for their high mineral content, so they have been used as feed and food supplements. In fact, they have 10-100 times the mineral content of traditional vege­tables (Arasaki and Arasaki, 1983; Nishizawa, 2002), with ash reaching levels of up to 55% on a dry-weight basis, whereas sweet corn has a content of 2.6% and spinach an excep­tionally high mineral content of 20% (Rupierez, Ahrazem et al., 2002). The mineral composi­tion varies according to phylum as well as such other factors as seasonal, environmental, geographical, and physiological variations.

The mineral iodine deserves particular attention because its concentration may reach quite high levels in certain brown algae—say, 1.2% of dry weight. For instance, Saccharina japonica (kombu) is an excellent source of iodine, so it has been used for centuries in China as a dietary iodine supplement to prevent goiter; most of it is dried and eaten directly in soups, salads, and tea or used to make secondary products with various seasonings (Lobban and Harrison, 1994). Furthermore, kelp was used as raw material for extraction of iodine in Ireland during the 17th century (Morrissey, Kraan et al., 2001). Nevertheless, excessive iodine intake in sen­sitive persons can trigger hyperactivity of the thyroid gland, similar to the myxoedema reac­tion (Holdt and Kraan, 2011), so brown alga consumption has to be limited. The main methods of extracting iodine from seaweed, such as incineration, blowout, ion exchange, and activated carbon adsorption, have been fully discussed and compared in terms of advan­tages and shortcomings by Jinggang et al. (Wang, Feng et al., 2008).