Safety Of Foods Containing Nitrites and Nitrates

A nitrate, salt of nitric acid, is a natural constituent of soil and vegetation. Nitrate is also a normal metabolite in mammals. Examples of nitrates include potassium nitrate, ammonium nitrate, calcium nitrate, calcium nitrate hydrated, and magnesium nitrate.

A nitrite is a salt of nitrous acid; it is also a normal metabolite in mammals. The average intake of nitrite is considerably less than that of nitrate. The main source is vegetables, just like that of nitrate. Vegetables will convert nitrate to nitrite on storage and when contaminated with bacteria that convert nitrates to nitrites. Occasionally, this can result in very high concentrations ov nitrites in vegetable juices in particular. The amount of nitrite ingested from food, however, is only a fraction of that swallowed as a result of nitrate conversion to nitrite in the mouth (average concentration of nitrite in saliva is 200 µM). Nitrite is used as a food preservative and coloring agent.

The major acute toxic effect of nitrate and nitrite poisoning is methemoglobinemia resulting in decrease of the oxygen-carrying capacity of the blood. The principal concern with exposure to nitrate is its biological reduction to reactive and toxic nitrite. Nitrate itself is rather harmless. Symptoms may include bluish discoloration of the skin the may appear within a few minutes to 45 minutes or more after exposure. Coma and convulsions in severe poisoning due to severe oxygen deprivation. Abnormally rapid heart rate, hypotension and collapse may also occur. Nausea, vomiting and abdominal pain may be seen.

Nitrite easily transforms into a nitrosating agent in an acidic environment and can react with a variety of compounds, e.g. ascorbic acid, amines, amides. Nitrosation can also be mediated by bacteria, e.g. in the stomach. Some reaction products are carcinogenic (e.g. most nitrosoamines and amides.