On the formation of N-nitrosopyrrolidine from potential precursors and nitrite

Several naturally occurring amino compounds, structurally related to pyrrolidine, were reacted with nitrite in heated, weakly acidic, aqueous systems and the amount of NPYR formed was measured. The study included amines, free amino acids and different proline-containing peptides. The yields of NPYR formed from pyrrolidine, putrescine, agmatine, spermidine, spermine, proline, ornithine and arginine with nitrite in the pH range 6.6 to 4.0 were determined. The lowest yields were obtained from the amino acids, due to slow decarboxylation. When proline peptides were heated with nitrite at pH 5.7 and 4.0, no NPYR was detected (except in the case of cyclo-(Pro-Pro-)), but at pH 3.4, small amounts of NPYR were formed from all tested peptides. Cyclo-(Pro-Pro-) yielded NPYR at pH 5.7 and 4.0, as well. It is suggested that, under certain conditions, N-nitrosation may occur during cleavage of a peptide bond in the presence of nitrous acid. The formation of NPYR and NPIP from proline, pyrrolidine, putrescine, spermidine and cadaverine was studied in a model experiment, using minced bacon as the reaction medium. The results show that the formation of NPYR and other volatile nitrosamines is possible in the aqueous phase of bacon during frying.