Nitrates and Nitrites in Leafy Vegetables: The Influence of Culinary Processing on Concentration Levels and Possible Impact on Health

Vegetables, as an important source of vitamins and minerals, are highly recommended in a healthy diet. At the same time, vegetables can contain elevated amounts of nitrates and nitrites, which are the possible nitrosating agents responsible for the formation of carcinogenic nitrosamines. In young children, they can cause methemoglobinemia. Determining the level of nitrates and nitrites, as well as the possible reduction in their concentrations during culinary processing, is especially important for the diet of young children, who are introduced to leafy vegetables during the first year. For some types of vegetables that are often found in the diet, maximum permissible concentrations have not yet been established. Our goal was to estimate the reduction factors of nitrates and nitrites and suggest the best ways to properly prepare foods. For this purpose, samples of Swiss chard, spinach, and white cabbage were collected from the market to determine the nitrate and nitrite content. Vegetable samples were subjected to culinary preparations: soaking, cooking, and a combination of soaking and cooking. Quantitative and qualitative determination of nitrates and nitrites in vegetables was carried out on high-performance liquid chromatography (HPLC) equipped with a diode array detector (DAD). The obtained results showed that the highest nitrate concentrations were in Swiss chard samples, followed by spinach, and the lowest in white cabbage samples. The impact of culinary preparation was highest on spinach samples. Considering the average nitrate concentrations achieved after cooking or soaking and cooking, there was no risk of exceeding the ADI limit. However, the ADI values would be exceeded at the maximum nitrate concentrations.