Volatile N-nitrosamines in fish meal, with special reference to the mechanism of formation of N-nitrosothiazolidine.

Volatile N-nitrosamines in 32 commercial Japanese fish meal samples were analysed, and three compounds, N-nitrosodimethylamine, N-nitrosopyrrolidine and N-nitrosothiazolidine (NT), were detected. We also examined the mechanism of formation of NT during fish meal production. Both cysteamine and thiazolidine were found to be precursors of NT. The cysteamine content decreased during boiling and drying of the fish; but that of thiazolidine increased during boiling. N-Nitrosothiazolidine 4-carboxylic acid (NTCA) was formed in sardine meal after treatment with nitrogen dioxide gas, and the rate of formation of NT from NTCA added to sardine meal was as high as 10% when the meal was heated at 160 degrees C for 60 min. We propose two pathways for NT formation during fish meal manufacture: (1) cysteamine----thiazolidine----NT; and (2) cysteine----(thiazolidine 4-carboxylic acid)----NTCA----NT.