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) for mation in cured meats following incubation with nitrite at gastric pH, we e xtended the investigation to other foods mentioned in the title of this pap er. The main objective was to determine whether these foods have the potent ial to form NMU at pH's that can be found in the human stomach. This was do ne by nitrosating an aliquot (5 g for fish sauce, 10 g for the others) of e ach with 7.25 muM: to 1.59 mM levels of sodium nitrite for 2 h at room temp erature at pH 0.8-1.5 and measuring the amounts of NMU formed. Of the sampl es 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 pate (<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 p ickled radish (<0.3-72 ng). Incorporation of 200-2000 ppm of ascorbic acid in the fish sauce and other foods, prior to nitrosation, appreciably inhibi ted such NMU formation. Although previous researchers in China reported NMU formation in nitrosated samples of fish sauce, this is the first reported formation of Nh;TU upon nitrosation of the other foods mentioned above, and the first reported inhibition of such formation by added ascorbic acid.