Dietary nitrate is also an important source of nitric oxide in mammals. Green, leafy vegetables and some root vegetables (such as beetroot) have high concentrations of nitrate.[11] When eaten and absorbed into the bloodstream, nitrate is concentrated in saliva (about 10-fold) and is reduced to nitrite on the surface of the tongue by a biofilm of commensal facultative anaerobic bacteria.[12] This nitrite is swallowed and reacts with acid and reducing substances in the stomach (such as ascorbate) to produce high concentrations of nitric oxide.