The blocking effect of phenolic acid on N-nitrosomorpholine formation in vitro.

Phenolic acids (PAs) are widely found in many daily consumed vegetables and fruits. The inhibitory effects of PAs on N-nitrosomorpholine (NMOR) formation in vitro under simulated gastric juice condition were studied. The results showed that the inhibitory potency of thirteen varieties of PAs differed greatly, which may be related to their chemical structures; the blocking rate (BR) of different kinds of PAs were as follows: caffeic acid, 92.5%; tannic acid, 90.0%; gallic acid, 86.8%; sinapinic acid, 86.2%; ferulic acid, 81.1%; chlorogenic acid, 69.4%; gentisic acid, 69.2%; syringic acid, 62.1%; protocatechuic acid, 56.0%; p-coumaric acid, 52.5%; vanillic acid, 35.4%; moreover, p-hydroxybenzoic acid and m-coumaric acid had the least blocking effect or even slight catalyzing effect. The results also demonstrated that amounts of NMOR formed were negatively correlated with molar ratio of PAs to nitrite and that the optimum pH for inhibition was between 2 and 3.