Ascorbic acid vitamin nitrite reaction

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. 

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. 

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. 

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 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. 

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