Precursors of N-Nitrosodimethylamine formed in Dried Squid upon Broiling

Abstract

The precursors of carcinogenic N-nitrosodimethylamine (NDMA) formed in dried squid products upon broiling on a city gas range have been studied. Concerning the nitrosating species such as nitrogen oxides (NO_X) and ethylnitrite produced upon broiling, the highest yields of these compounds were observed in the gases produced by combustion of kerosene, followed by those from city gas combustion. We have examined the nitrosation reactions between various amines occurring naturally in the squid muscle and nitrogen dioxide (NO₂) in vitro. No appreciable amount of NDMA was formed from betaine or dimethylglycine, and only trace quantities could be detected with sarcosine. The highest reaction rate of an amine with NO₂ to form NDMA was found to occur with dimethylamine (DMA, the yield was 48.6%), followed by trimethylaminoxide (TMAO, the yield, 1.1%). The average TMAO-N content of uncooked squid sample was as high as 2580 mg/kg, while the initial level of DMA was only 39.4 mg/kg, and it became 54.8 mg/kg after broiling. Judging from the initial levels of these amines, and the reaction rates of NDMA formation, it may be concluded that the most important and principal precursor of NDMA in dried squid is TMAO.