Arseno lipids in salmon are partly converted during cooking
An international group of researchers investigated the effect of cooking salmon on the speciation of arsenolipids naturally present in fresh fish. The speciation analysis performed revealed that arsenic hydrocarbons are partly converted to their thioxo analogs.
Fish is considered to be an important part of healthy diet because it contains nutrients associated with beneficial health effects such as polyunsaturated fatty acids. However, fish also contribute substantially to dietary arsenic, which is considered one of the trace elements of most concern with respect to human health. A great variety of arsenic compounds have been found in fish including inorganic arsenic forms, water-soluble organoarsenicals, and lipid-soluble arsenolipids all differing in their toxicity. While inorganic arsenic species are highly toxic, their concentration in fish is generally too low for creating a health hazard. On the other side the high concentration of water-soluble arsenic species, often mainly present as arsenobetaine, are considered harmless. Unfortunately, the same low toxicity has not been observed for the arsenolipids. Especially, one group of arsenolipids, the arsenic-containing hydrocarbons has cytotoxicity comparable to that of inorganic arsenic. Because of such toxicity, risk assessments of arsenolipids in seafood have been performed. Yet such evaluation has focused on raw products, and the effect of food preparation such as cooking or frying has not been assessed for these compounds.
The new study:
To close such gap, an international group of researchers investigated the changes taking place to arsenolipids during either baking or steaming salmon. Speciation analysis has been performed by using HPLC coupled with both inductively coupled plasma mass spectrometry (ICP-MS) and electrospray mass spectrometry (ESMS) to determine the arsenic species before and after cooking.
Salmon fish fillets were either cooked by baking in the oven at 200°C for 15 min., or by steaming at 100°C for 5 min. Both cooked and raw fish fillets were frozen at -80 °C and then freeze dried to constant dry mass. A portion of the dried fish powder was then extracted with hexane, the hexane was evaporated and the oily residue was extracted with ethanol. The remaining fish pellet was then extracted with water. Both the ethanol and water extracts were then analyzed by HPLC with mass spectrometric detection, using reversed-phase HPLC-ICP-MS/ESMS for the ethanol extracts and a cation exchange HPLC-ICP-MS for the aqueous extracts.
Figure: Chemical structure of 1-(dimethylarsinyl)pentadecane (oxo-AsHC 332) and 1-(dimethylarsinyl-sulfanidyl)pentadecane (thioxo-AsHC 348).
The speciation analysis revealed that about 6% of the total arsenic was lipid-soluble, consisting of three arsenic hydrocarbons (oxo-AsHC 332, oxo-AsHC 360, and oxo-AsHC 405, together 55% of the arsenolipid fraction) and a band of unidentified less-polar arsenolipids (ca 40%) together with trace amounts of 6 other species. The comparison between raw and cooked fish fillets revealed that about 28% of the oxo-AsHC were converted to their thioxo analogs.
The authors concluded that the greater lipophilicity of the thioxo analogs could alter the mode of toxicity of the arsenic hydrocarbons which should be considered in future regulations related to food safety.
The original publication
Chan Xiong, Ronald A. Glabonjat, Md Hasan Al Amin, Michael Stiboller, Jun Yoshinaga, Kevin A. Francesconi, Arsenolipids in salmon are partly converted to thioxo analogs during cooking, J. Trace Elem. Med. Biol., 69 (2022) 126892. DOI: 10.1016/j.jtemb.2021.126892
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