Foods nitrite/nitrate addition

Human exposure to nitrates is via exposure to food and drinking water. The nitrates in food may be present naturally or as an additive introduced for various technological reasons. Nitrite is added to foods for preservation, but is reactive in foods, whereas nitrate is quite unreactive. 

It should be added that food additives are not the only source of nitrates and nitrites. Nitrate is widely used as a fertiliser in agriculture and reappears in water and in a number of vegetables and no doubt in other foods. This source of nitrites in the diet will have to be given serious consideration in any final analysis . 

N-Nitrosamines, formed principally from the reaction of naturally occurring secondary amines with nitrites that may be added to foods or produced by bacterial reduction of nitrates, have been identified in many food systems including cured meat products, nonfat dried milk, dried malt and beer. In addition, the presence of less volatile and non-volatile N-nitroso compounds or their precursors in foods have been suggested from a number of model system studies. 

This technique has been established for many years particularly for water, soil and feeding-stuff analysis, where a large number of analyses are required for quality control or monitoring purposes. A number of applications have been published for food additives including aspartame (Fatibello et al., 1999), citric acid (Prodromidis et al., 1997), chloride, nitrite and nitrate (Ferreira et al., 1996), cyclamates (Cabero et al., 1999), sulphites (Huang et al., 1999 AOAC Int, 2000), and carbonate, sulphite and acetate (Shi et al., 1996). Yebra-Biumm (2000) reviewed the determination of artificial sweeteners (saccharin, aspartame and cyclamate) by flow injection. 

In foodstuff preserved by addition of nitrate/nitrite (namely cured meat produce and cheeses) both methods of preservation introduce nitrosating species into the food matrix. 

The U.S. Food and Drug Administration (FDA) regulates the addition of nitrate and nitrite salts to fish products. Maximum permitted levels vary among products and types of fish, with up to 500 ppm residual sodium nitrate or 200 ppm sodium nitrite permitted as a preservative and color fixative in smoke cured sable fish, shad, or salmon (Code of Federal Regulations, 1981a,b Committee on Nittite and Alternative Curing Agents in Food, 1981). 

Although the potentially carcinogenic nitrosamines may he present in foods, particularly cured meats, occurrence is infrequent and at low levels. USDA regulations stipulate that ascorbic acid be added to cured meats at live limes the level of nitrates and nitrites to prevent the formation of carcinogenic Af-nitroso compounds. See also Food Additives. 

Statutory legislation to control the levels of such substances in food has been introduced in the UK and elsewhere. In more recent years, other potentially toxic elements have come into focus. Lead, cadmium and mercury have been the subject of much monitoring of the food chain and other metals, in particular aluminium, are continuing to attract attention. Nitrate and nitrite in food from food additive use is regulated across the European Union, but its presence in food crops has raised concerns. 

ELLEN G, EGMOND E, VAN LOON J W, SAHERTIAN E T and TOLSMA K, Dietary intakes of some essential and non-essential trace elements, nitrate, nitrite and N-nitrosamines by Dutch adults estimated by a 24-hour duplicate portion study , Food Additives and Contaminants, 1990 7 207-22. 

There are two kinds of preservatives, class I and class II. Class I preservatives include common salt, sugar, glucose/sucrose syrup, acetic acid or vinegar, spices, and wood smoke. The addition of these to foods is not restricted. Class II preservatives include benzoic acid and its salts, nitrates and nitrites, sorbic acid and its salts, and sulfurous acid and its salts. Their addition to food is, however, restricted. 

Batina, R, Fritsch, R, de Saint, B., and MitjavUa, M.T. 1990. In vitro kinetics of the oxidative reactivity of nitrate and nitrite in the rat erythrocyte. Food Additives Contaminants Part A, 1 145-9. 

In addition to dietary sources, a significant amount of nitrate is formed endogenously by the metabolism of nitric oxide - 1 mg per kg of body weight per day (about the same as the average dietary intake), increasing 20-fold in response to inflammation and immune stimulation. There is considerable secretion of nitrate in saliva, and up to 20% of this may be reduced to nitrite by oral bacteria. Under the acidic conditions of the stomach, nitrite can react with amines in foods to form carcinogenic N-nitrosamines, although it is not known to what extent this occurs in vivo. 

However, questions have been raised about the possible effects of these additives on human health. Nitrites, for example, appear to decrease the ability of a young child s blood to carry oxygen. In addition, nitrites combine with organic compounds known as amines to form a family of toxic compounds known as the nitrosoamines. These hazards have prompted some scientists and nonscientists alike to call for the ban of nitrates and nitrites as food additives. 

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