Catalysis and inhibition of N-nitrosation reactions.

A number of factors that can lead to an acceleration or inhibition of N-nitrosation reactions may play an important role in the formation of N-nitroso compounds in foods and other environmental samples and in the body. The anion thiocyanate is a particularly effective catalyst for nitrosamine formation. It occurs in normal human saliva, but at higher concentrations in the saliva of smokers. Although nitrosation reactions are accelerated in the normal manner with increasing temperature, rate enhancements are also observed in frozen systems, a phenomenon that may be important in frozen foods. Surfactants that form micellar aggregates can accelerate the nitrosation of hydrophobic amines. This may be important in foods in view of the presence of components such as lecithin, or in the body in view of the occurrence of bile acid micelles. Nitrosation reactions may also be accelerated in the presence of certain carbonyl compounds, thiols and nitrosophenols. A number of compounds readily convert nitrosating agents into innocuous products and hence inhibit nitrosation reactions. If reductones such as ascorbic acid are present, they may react much faster with nitrous acid than amines and therefore effectively scavenge the nitrosating agent. Rapid reaction of polyhydroxyphenols with nitrous acid is another example of how endogenous or exogenous nitrosation reactions may be inhibited. Many microorganisms can influence nitrosation reactions by converting nitrate to nitrite, a reaction that can take place in foods, but which is particularly important in the body.