Nitrate is a natural compound that accumulates in leafy vegetables. High levels of nitrate and nitrite in food can cause some health effects such as methaemoglobinemia and gastric cancer. Thus, the European Regulation No. 1881/2006 established maximum limits for nitrate levels in different types of leafy vegetables such as spinach, lettuce and wild rocket. Nitrite should be present in these vegetables only in traces. However, some recent studies demonstrated that these levels can also reach high levels, higher than 100 mg kg-1. The food safety concern in then related not only to the compliance of nitrate level with the legal limit but also to the possible presence of nitrite at high level. In this last case, the scenario is more complex, since no legal limit is defined, and nitrite is considered as the direct precursor of N-nitrosamines, well-known pro-carconogenic conpounds.
In this monitoring, 230 samples of leafy vegetables (75 lettuce, 75 spinach, 50 swiss chard and 30 wild rocket) were collected on the Italian market and then analysed for the determination of nitrite and nitrate by using validated and accredited analytical techniques based on ion chromatography with conductivity detection. The first technique, based on traditional ion chromatography, was used for analysing all samples, the second, based on capillary ion chromatography, was used for confirmation of analytical results whne the samples showed nitrate concentration higher tha the legal limit and/ot nitrite concebtration higher than 50 mg kg-1.
Nitrites were detected at high concentrations, in the range 66.5-219.5 mg kg-1 wet weight, in 7 samples (1 lettuce, 3 spinach, 1 swiss chard and 2 wild rocket), confirming that further EU limits and new research are needed on this type of contamination. This research should be especially focused on the individuation of the mechanisms responsible for the formation of such compound, and the elaboration of specific strategies for industry focused at eliminating/reducing the presence of nitrite in leafy vegetables. Regarding nitrate, concentrations higher than the respective EU limits were detected in 20 samples (5 lettuce, 4 spinach and 11 wild rocket), confirming the need of official control. Interesting results were also obtained for swiss chard, in which, despite no EU limit have been defined so far, the average nitrate level resulted higher than those recorded for spinach and lettuce. This results suggests the definition of EU limits also for this type of leafy vegetable.
This work was supported by the Italian Ministry of Health who financed the Research Project code IZSPB 07/20 RC.