Abstract
A quantitative measure of the amounts of nitrosatable compounds present in various foods was obtained by reacting whole foods with a large excess of sodium nitrite and studying the amount of N-nitroso compounds formed. This treatment produced several volatile N-nitrosamines, identified by combined gas chromatography - mass spectrometry, although the major products were non-volatile nitrosamines of unknown identity. To obtain a measure of the probable nitrosation that may occur in the human stomach, after a nitrite-containing meal is consumed, the same foods were exposed to low concentrations of sodium nitrite (10 and 100 ppm.) in a medium simulating the human stomach. Under these conditions nitrosation of foods did occur, the products being mainly non-volatile N-nitroso compounds. 'In vivo' studies were performed, where nitrite-containing meals were fed to humans. No nitrosation could be detected and it was observed that the ingested nitrite disappeared rapidly from the stomach contents. Studies, in which dogs were fed large amounts of nitrite and amine, resulted in the formation of the corresponding N-nitrosamine in the stomach. The catalysis of nitrosations by various biological anions was examined. None of the anions tested produced a marked catalytic effect and thiocyanate remains the most effective catalyst. Concentrations of thiocyanate, comparable to levels found in human saliva, were incorporated into incubations of food with nitrite in the simulated stomach medium, but there was no great enhancement in the amount of nitrosation that occurred. The possible nitrosation of peptide bonds was studied, using glycyl glycine. It was demonstrated that an N-nitroso derivative could be produced, although its yield was low. It was shown that other peptide bonds could also be nitrosated, but the nature of the constituent amino acids did not markedly affect the nitrosation. Several amines present in foods, were examined for their potential for nitrosation.