Vitamin reaction with nitrite

The loss of vitamin C may also occur during reactions of ascorbic acid with some of the reactive food components. In particular, reactions of ascorbic acid with quinones generated by enzymatic browning reactions, reactions with nitrites and haem pigments in meat and meat products are technologically significant. 

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. 

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. 

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. 

The nitrosation of several secondary and tertiary amines can be blocked in vitro by the addition of vitamin C. The vitamin appears to compete for the nitrite, thus inhibiting nitrosation. It has been demonstrated that vitamin C does not react with amines, nor does it enhance the rate of nitrosamine decomposition. However, it reacts very rapidly with nitrite and nitrous acid. It has been suggested that the vitamin decreases the available nitrite by reducing nitrous acid to nitrogen oxides, leading to inhibition of the nitrosation reaction ... 

Since the synthesis of N-nitroso compounds is accomplished through reaction of secondary amines and nitrous acid, it was demonstrated that nitrosamines could be produced biochemically by the naturally acidic conditions in the stomach with ingestion of secondary amines (2). The nitrosating agent would be formed by the reaction of gastric juice with nitrite compounds that are widely used as food preservatives and for food color enhancement (2). Vitamin C was found to be a potent inhibitor of this reaction (I). 

Nitrosamines are produced in foodstuffs from reactions of nitrites (added as preservatives to bacon and other processed meat products) with amines in (or derived from) the foodstuff, particularly during cooking, e.g., frying anti-oxidants such as ascorbic acid (vitamin C) are added to such foodstuffs to inhibit formation of nitrosamines. A source of nitrosamines that may be of interest to some analytical chemists is beer, in this case attributed (Sen 1983) to reaction of nitrogen oxides with alkaloids (usually present in germinated malt) during the drying process. NMDA can also be formed inadvertently in a number of industrial processes. 

Proteins are the most reactive of the major food components and, apart from the destruction of certain vitamins, reactions between food proteins and other food components are the major chemical interactions that occur during processing. Proteins can react with reducing sugars, fats and their oxidation products, polyphenols, vitamin and with various chemical additives such as nitrites, aldehydes and alkali (Fig. 1). These reactions can lead to a reduction... 

Hydroxocobalamin (vitamin another antidote, is a potential alternative to sodium nitrite treatment. It works by binding with cyanide to form nontoxic cyano-cobalamin (vitamin Bj ). Although effective and relatively safe in experimental models, the concentration available in the United States requires large infusion volumes and has a short shelf life due to light instability, and reports of anaphylactoid reactions have limited its use (8,13,21). Further studies using higher concentrations available in European formulations may eventually lead to its use as an outpatient alterative to sodium nitrite treatment in the United States (7,32). Other alternatives currently used or undergoing clinical trials in Europe include cobalt salts, limited by their toxicity, aldehydes, and aminophenol derivatives. These alternative treatments are not currently available in the United States (7). 

The reaction of vitamin C and 6-0-stearoyl ascorbic acid with various stable vitamin E radicals has been monitored spectrophotometrically using a stopped-flow technique. The reaction was dramatically slowed by steric hindrance about the aryloxy radical.87 Sodium nitrite has been shown to accelerate the decomposition of ascorbic acid under aerobic conditions, and an ascorbate-nitrile complex was observed by nmr.88... 

The major chemical reactions that take place during food processing, as would be expected, occur between the main food components—the carbohydrates, proteins, fats and vitamins. These components can react with each other and with various food additives such as nitrites, sulphite, aldehydes and alkali to give food products of lower nutritional value to produce desirable and undesirable browning and flavours and very occasionally to produce toxic materials. 

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