Inhibition of N-nitrosation of secondary amines in vitro by tea extracts and catechins

Inhibition of nitrite-mediated N-nitrosation of dimethylamine, morpholine and N-methylaniline by tea extracts and by 6 individual catechins in the extracts was studied. The inhibitions were detected by quantifying the nitrosamines formed. Eight different kinds of teas (5 green teas, a roasted green tea, an oolong tea, and a black tea) were examined for their inhibitory abilities and for their catechin contents, with an attempt to correlate the inhibitory activities to the catechin contents. The results showed that (1) the green tea extracts inhibit strongly the N-nitrosation of the three secondary amines tested, (2) the 6 catechins, notably epigallocatechin, are capable of blocking the N-nitrosations very efficiently, even more efficiently than ascorbic acid, and (3) the inhibition activities of green tea extracts are mostly ascribable to the catechins present in the extracts. These inhibitions occur by rapid reactions between nitrite and the catechins. It was observed that no mutagenicity results from the reaction between the tea extracts and nitrite. (C) 1998 Elsevier Science B.V.