Possible causes of high nitrite levels in some processed leafy vegetables

Abstract

Nitrate is a compound that accumulates in the leaves of some leafy vegetables such as spinach, lettuce and rocket, and the European Regulation No. 2023/915 establishes maximum limits, due to some health effects. Nitrite should be absent or present only in traces in leafy vegetables. However, some recent studies demonstrated that not negligible concentrations of nitrite (higher than 50 mg kg−1) may be quantified in leafy vegetables such as spinach and lettuce. In this work, several possible sources of nitrite formation in leafy vegetables, agronomic, environmental, microbiological, and processing have been investigated to evaluate the main factors which led to this accumulation. Microbiological contamination, particularly Enterobacteriaceae, of “fresh-cut” samples of spinach, Swiss chard and wild rocket, has been ascertained as the main source of nitrite accumulation, regardless of other considered factors (agronomic, environmental, processing, etc.). The correlation between Enterobacteriaceae count and nitrite concentration was assessed at 0.98, confirming this one as the main source of nitrite increase, also at very high levels, in processed leafy vegetables.