Nitrosamine, vitamin

Inhibition of nitrosation is generally accompHshed by substances that compete effectively for the active nitrosating iatermediate. /V-Nitrosamine formation in vitro can be inhibited by ascorbic acid [50-81-7] (vitamin C) and a-tocopherol [59-02-9] (vitamin E) (61,62), as well as by several other classes of compounds including pyrroles, phenols, and a2iridines (63—65). Inhibition of iatragastric nitrosation ia humans by ascorbic acid and by foods such as fmit and vegetable juices or food extracts has been reported ia several instances (26,66,67). 

Ascorbic acid and alpha-tocopherol are effective blocking agents against N-nitroso compound formation. Ascorbic acid is effective particularly in aqueous media, and tocopherol effective particularly in lipid phases. They should be used in conjunction due to the mutually complementary actions of the two vitamins in blocking nitrosamine formation in both aqueous and lipid media. 

In addition to vitamin C and vitamin E as effective blocking agents, there are other substances which also are capable of preventing nitrosamine formation which are present in normal foods. The influence of this factor on the design of experimental studies should not be overlooked. 

Mirvish (53,54) discovered that vitamin C could inhibit ni-trosation reactions. The purely chemical interaction of ascorbic acid with nitrite has been studied for theoretical reasons and because of its importance in the preservation of foods. This interaction has received increased attention for minimizing the presence of nitrosamines and nitrosamides in the environment, and especially in foods. We have studied the relationship in gastric carcinogenesis between high levels of nitrite, including pickling, and of vitamin C as a protective and inhibiting element. 

If the concepts and facts presented in this paper are correct, a major kind of human cancer in many regions of the world, cancer of the stomach, is due to a type of nitroso compound, a nitrosoureido derivative, even though not a nitrosamine It is quite certain that the formation of such compounds can be blocked by vitamin C and vitamin E, as well as by some other substances such as gallates Thus, the primary prevention of cancer caused by nitroso compounds is readily accomplished through an adequate Intake of such harmless inhibitors with every meal from infancy onwards ... 

Inhibitors of nitrosation generally function by competing with the amine for the nitrosating agent. An inhibitor would thus react with nitrite at a faster rate than with amines. The inhibition reaction has recently been reviewed ( 35). The ability of ascorbate to act as a potent inhibitor of nitrosamine formation has resulted in the use of the vitamin in nitrite-preserved foods and pharmaceuticals. Furthermore, the effectiveness of ascorbate in inhibiting nitrosamine formation is dependent on (1) the concentration of ascorbate (an excess is required) (2) pH (ascorbate is nitrosated 240 times more rapidly than ascorbic acid) (3) the reactivity of the amine toward nitrosation and (4) the extent of oxygenation of the system. 

Antioxidant activity involving the transfer of two electrons between the ascorbate/dehy-droascorbate redox couple or donation of one electron to inactivate highly reactive free radicals, e.g., protection of vitamin E by reduction of the tocopheryl radical Competitive inhibition in substrate binding reactions, including inhibition of the formation of carcinogenic nitrosamines... 

The first edition of Food Analysis by HPLC fulfilled a need because no other book was available on all major topics of food compounds for the food analyst or engineer. In this second edition, completely revised chapters on amino acids, peptides, proteins, lipids, carbohydrates, vitamins, organic acids, organic bases, toxins, additives, antibacterials, pesticide residues, brewery products, nitrosamines, and anions and cations contain the most recent information on sample cleanup, derivatization, separation, and detection. New chapters have been added on alcohols, phenolic compounds, pigments, and residues of growth promoters. 

Diet from a certified producer only should be used. The composition of the diet should be described in an analytical certificate with regard to nutritional constituents (carbohydrates, fat, protein, vitamins, minerals) and for contaminants (nitrosamines, alia-... 

As discussed in Section 13.3.6, ascorbate may act to inhibit the formation of carcinogenic nitrosamines from nitrite and dietary amines, and thus reduce the risk of cancer. There is some evidence that vitamin C supplements are protective against the development of gastric cancer. 

Three cases that demonstrate the value of additional research are the eflFects of smoking on the rate of ascorbic acid metabolism, as described in chapter 16 in this book the increase in the RDA for vitamin C in 1980 over that in 1974 on the basis of the significant improvement in iron absorption (40) and the blocking of nitrosamine production as described in chapter 24 in this book. 

Review of Ascorbic Acid Mechanisms of Action. Ascorbic acid and AP have antioxidant activity in fats, oils, vitamin A, and carotenoids. In these systems AP is a better antioxidant than are the phenolic antioxidants BHT and BHA, both from these data and others (29,35). Ascorbic acid protects against oxidation of flavor compounds in wine, beer, fruits, artichokes, and cauliflower (29) presumably by oxygen scavenging. The well-known formation of nitric oxide from nitrites by ascorbic acid is used not only for inhibition of nitrosamine fortnation, but also to promote... 

Nitrites are generally not classified as human carcinogens. Under certain conditions nitrites may combine with amines in the body to form nitrosamines. There are a number of different nitrosamines many are regulated as human carcinogens. Certain chemicals, such as vitamin C (ascorbic acid), can limit the transformation of nitrites to nitrosamines. US Department of Agriculture (USDA) requires the addition of ascorbic acid or erythorbic acid to bacon cure to reduce the risk of nitrosamine formation. 

Since nitrosamines and their precursors are present in the food, exposure to nitrosamines cannot be avoided. Flowever, recent studies have shown that ingestion of adequate quantities of vitamin E and selenium may reduce the risk of cancer. It is known that carcinogenic nitrosamines are formed from the reaction of some amines with nitrites and nitrates present in the diet. Vitamin E and selenium have been found to minimize or prevent the reaction of nitrites/ nitrates with amines and hence prevent or reduce the formation of carcinogenic nitrosamines. 

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