Decrease of arsenic in edible brown algae Hijikia fusiforme by the cooking process

Overview

Ichikawa and colleagues measured total arsenic and arsenic species in edible brown algae Hijikia fusiforme and tested arsenic removal by soaking and cooking. The source is directly relevant to hijiki/seaweed occurrence because it reports dry-weight total arsenic and measured As(V), As(III), DMAA, and arsenosugar fractions across samples from Japan, South Korea, and China. The mouse metabolism experiment is exposure context, not product occurrence.

Key numbers

All concentrations below are reported by the source in µgAs/g, dry weight; no unit conversion was performed.

Total arsenic in Table 2:

Arsenic speciation in Table 3:

The source states that inorganic arsenate was the main species in hijiki, and that the ratio of inorganic to organic arsenic was 55.4-88.1%. Minor components were inorganic arsenite (0-28.1%), dimethylarsinic acid (0.6-4.8%), and arsenosugar (0.9-3.1%).

Soaking/cooking removal from Table 4:

The abstract and results state that 28.2-58.8% (w/w) of total arsenic in hijiki was eluted with soaking water, 49.3-60.5% (w/w) of arsenic in the residue was dissolved by cooking, and 88.7-91.5% (w/w) of arsenic was removable by the full cooking process. The source also states that 75.0-81.4% of the eluted arsenic was arsenate.

Mouse metabolism context:

• After administration of soaking water, arsenate was metabolized to DMAA in urine.
• After cooked hijiki administration, arsenate and DMAA were excreted in urine.
• Administered arsenosugar was metabolized to DMAA with five unknown compounds in urine.

Methods (brief)

Hijiki sprout and long-portion samples came from Japan, South Korea, and China via the Hijiki Cooperative Society Japan. For total arsenic, uniform hijiki powder was digested with nitric acid, hydrogen peroxide, sulfuric acid, ammonium hydrogencitrate, hydrochloric acid, ascorbic acid, and potassium iodide, then measured by hydride-generation atomic absorption spectrometry. Arsenic speciation used HPLC/ICP-MS with an Inertsil AS column and standards for arsenate, arsenite, MMA, DMAA, arsenobetaine, TMAO, tetramethylarsonium, arsenocholine, and synthesized arsenosugar.

The preparation experiment soaked 5 g dried hijiki in 20 mL pure water for 30 min at room temperature, then boiled the soaked hijiki in 30 mL pure water for 20 min at 90 °C. Extracts were filtered through 0.2 µm filters before speciation analysis. The mouse experiment used an arsenic-free diet before administration and collected urine/feces for arsenic-species analysis; those biological matrices are not treated as product occurrence values here.

Related evidence

• Seaweed/kelp foods (nori, wakame, kombu, dulse — as food products)
• Seaweed
• Arsenic, Total
• Arsenic, Inorganic

Update history

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