Formation of N-nitroso-N-methylurea in various samples of smoked/dried fish, fish sauce, seafoods, and ethnic fermented/pickled vegetables following incubation with nitrite under acidic conditions.

In continuation of our previous studies on N-nitroso-N-methylurea (NMU) formation in cured meats following incubation with nitrite at gastric pH, we extended the investigation to other foods mentioned in the title of this paper. The main objective was to determine whether these foods have the potential to form NMU at pH's that can be found in the human stomach. This was done by nitrosating an aliquot (5 g for fish sauce, 10 g for the others) of each with 7.25 microM to 1.59 mM levels of sodium nitrite for 2 h at room temperature at pH 0.8--1.5 and measuring the amounts of NMU formed. Of the samples tested, fish sauce formed 2--712 ng of NMU, followed in decreasing order by herring (<0.3--688 ng); dried anchovy, shrimp, and other fishes (<0.3--134 ng); crab and lobster paté (<0.3--342 ng); sardines (6--59 ng); oysters and mussels (11--31 ng); dried squid (3--47 ng); kimchi (7--107 ng); and Japanese pickled radish (<0.3--72 ng). Incorporation of 200-2000 ppm of ascorbic acid in the fish sauce and other foods, prior to nitrosation, appreciably inhibited such NMU formation. Although previous researchers in China reported NMU formation in nitrosated samples of fish sauce, this is the first reported formation of NMU upon nitrosation of the other foods mentioned above, and the first reported inhibition of such formation by added ascorbic acid.