Characterization of N-(nitrosomethyl)urea in nitrosated fermented fish products

To characterize chemical carcinogens in acidic-nitrosated fish sauce sample, N-nitrosamides in the sample were separated by two kinds of reversed-phase HPLC columns, and with detection by photolysis-pyrolysis-thermal energy analyzer. A strong chromatographic peak at t(R) 12 or 4.5 min, same as that for N-(nitrosomethyl)urea (NMU), was obtained on PRP-1 or C-18 HPLC column from fish sauce sample with 10 mM trifluoroacetic acid as the basic mobile; acetonitrile, as organic modifier after the sample was nitrosated by 5 mmol/L of sodium nitrite (final concentration) at 37 degrees C and pH 2.0 for 1 h. No response above t(R) could be observed from the nitrosated sample in the detection system without photolysis. Such a peak could not be obtained from the unnitrosated fish sauce either. These results indicated that the component was NMU. Furthermore, this component, NMU, could also be detected in the nitrosated human gastric juice sample spiked with fish sauce. The formation of NMU in the sample was pH- and nitrite-dependent. This paper provides direct evidence that NMU formation could occur in fish sauce from the high-risk area for stomach cancer and in the fish sauce spiked human gastric juice during nitrosation under simulated gastric conditions.