Effect of the cooking procedure on the arsenic speciation in the bioavailable (dialyzable) fraction from seaweed

Abstract

Seafood, including edible seaweed, contains high levels of arsenic. The intake of seaweed is a route to arsenic exposure. Due to the different toxic behaviors among arsenic species, speciation studies are a matter of vital importance to evaluate possible health risks for consumers. Most seaweeds are ingested after a heat treatment and these thermal procedures could lead to a change in arsenic speciation. In this work an arsenic speciation study of four edible seaweeds (Kombu, Wakame, Nori and Sea Lettuce) after cooking has been performed by anion-exchange HPLC connected to an ICP-MS for arsenical detection. Speciation studies were also carried out in the cooking waters of those samples. Powdered cooked seaweed was subjected to an in-vitro digestion procedure by using Piperazine-NN-bis (2-ethane-sulfonic acid) disodium (PIPES), as a buffer solution at a pH of 7.0 and dialysis membranes of 10kDa molecular weight cut off (MWCO). Dialyzable fractions were analyzed to identify the arsenic species that become bioavailable for human body functions. Total arsenic concentrations were found between 5.3 and 79.1μgg−1, 3.6–36.7μgg−1 and 1.8–54.3μgg−1 for raw and cooked seaweed, and cooking water, respectively. Total arsenic bioavailability percentages were 20%, 29%, 18% and 11% for cooked Kombu, Nori, Wakame and Sea lettuce, respectively. Results suggest that the heat treatment and the acidic environment and enzymes used in the in-vitro gastrointestinal digestion are not sufficient to produce a change in the arsenic species of the four seaweeds studied. Arsenic species are comparable in each seaweed before and after being cooked, their cooking water and dialysate. Arsenosugars were the main arsenic species found. As(III) species and arsenobetaine (AB) were only found in the Sea Lettuce sample. Glycerol sugar and sulfonate sugar were the most bioavailable species for cooked Kombu and Wakame. Phosphate sugar showed to be in highest proportion in the dialyzable fraction of Nori. AB and glycerol sugar became more bioavailable in the Sea Lettuce sample.