Temperature-dependent extraction of trace elements in edible brown alga hijiki, Hizikia fusiforme

Trace elements were extracted from natural hijiki by heating with water (25–95 °C) or commercial hijiki by soaking, washing, and rinsing with water at room temperature. Eleven elements (As, B, Cd, Ce, Cu, Fe, Li, Sn, Tl, Y and Zn) were determined with ICP-MS in the acid-digested and diluted solutions of commercial/natural hijiki or in the water extracts of natural hijiki. Extractions were effective in removing metals in the range 55–65 °C. The traditional procedure of soaking and washing commercial hijiki was inadequate to sufficiently lower trace elements. The iron concentration in commercial hijiki was high, indicating a possible contribution from the iron cauldron used in producing commercial hijiki. Results showed unsuitability of the commercial production process for reducing trace elements sufficiently. To lower trace elements, a procedure involving two steps was proposed for preparing consumable hijiki. Hijiki may be recommended as a supplement for deficiencies of B, Fe, Cu and Zn.