Occurrence, formation and precursors of N-nitroso compounds in the Japanese diet.

A survey has been made of volatile nitrosamines in 123 fermented foods. These included salt-fermented vegetables, soy sauce, "miso", Japanese "sake" and other fermentation products. No appreciable amount, or only trace quantities, of NDMA and NPYR were detected in vinegar, "sake", wines and whiskies, while minute quantities of NDMA were detected in 31 out of 33 beer samples, where the levels ranged from traces to 13.8 micrograms/l, with an average of 5.1 micrograms/l. The nitrosamine content of salt-dried fish apparently increased when these products were broiled in a city gas range. A method for the determination of N-alkylureas in foods has been developed. A total of 57 food samples, both uncooked and broiled in a gas range or fried, were analysed. No alkylureas could be detected in these samples.