Nitrosation nitrite/nitrate addition

In order to define the conditions of the growing cultures, buffered medium (VL) inoculated with E, coli ATCC 11775 and supplemented with nitrate, glucose and DMA was incubated at 37 C, and pH, nitrite concentration, nitrate concentration, cell growth and nitrosamine formation were followed (Fig. 1). Within 2 hrs, >90% of the nitrate is converted to nitrite (some of the nitrite is further reduced) and over 8 hrs the pH drops from 7.3 to 6.0. This would indicate that in experiments carried out for 20 hrs or more the control medium should be adjusted to pH 6.0 to 6.5 and nitrite should be added rather than nitrate. Such a control medium (VL) was supplemented with nitrite and DMA and NDMA formation was followed (Fig. 2). It can be seen that even without the addition of cells the rate of nitrosation is 4 fold greater than... 

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 general mechanism of nitrosation of secondary amines is shown in Figure 12.26. Nitrosation reagents are formed in acidic solutions from nitrous acid and nitrites, respectively, by a sequence of reactions indicated in Figure 12.27. Nitrites are present in foods as additives or contaminants. In foods and beverages obtained by fermentation, nitrites may arise by reduction of nitrates by microbial reductases. In beer, for example, wild yeasts partly assimilate nitrates to give ammonia, and the activity of nitrate reductase... 

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