Characterization of nitrated phenolic compounds for their anti-oxidant, pro-oxidant, and nitration activities

Coffee is one of the most widely consumed beverages worldwide. Evidence of the health benefits and the important contribution of coffee brew to the intake of anti-oxidants in the diet has increased coffee consumption. Chlorogenic acid (ChA) and caffeic acid (CaA) are the major phenolic compounds in coffee. However, phenolic compounds, which are generally effective anti-oxidants, can become pro-oxidants in the presence of Cu2+ to induce DNA damage under certain conditions. On the other hand, sodium nitrite (NaNO2) is widely used as a food additive to preserve and tinge color on cured meat and fish. It is possible that phenolic compounds react with NaNO2 under acidic conditions, such as gastric juice. In this study, we identified compounds produced by the reaction between ChA or CaA in coffee and NaNO2 in artificial gastric juice. The identified phenolic compounds and nitrated phenolic compounds were assessed for their anti-oxidant, pro-oxidant, and nitration activities by performing an in vitro   assay. The nitrated phenolic compounds seemed to show increased anti-oxidant activity and decreased pro-oxidant activity. However, one nitrated CaA compound that has a furoxan ring showed the ability to release NO2- in the neutral condition.

► We identified the characteristics of compounds generated by reacting ChA, or CaA with NaNO2 in artificial gastric juice.
► All the compounds existed stably under the acidic condition.
► The nitrated phenolic compounds seemed to increase anti-oxidant activity and decrease pro-oxidant activity.
► 2-Oxy-3-(3,4-dihydroxyphenyl)-1,2,5-oxadiazole, which has a furoxan ring, increased NO2- in the neutral condition.