Nitrite, nitrate and N-nitrosamine occurrence in processed nitrate accumulating vegetables stored under different conditions

Nitrite, nitrate, and N-nitrosamines (NAs) have been extensively studied for their potential health risks; however, significant gaps remain in dietary exposure assessments, particularly due to the lack of occurrence data for many food categories including vegetables. Most studies have focused on processed meats, creating a need to explore other food sources to better estimate total dietary exposure. Leafy green vegetables, particularly when processed and stored, may accumulate significant nitrite and NA concentrations due to their naturally high nitrate content, contributing to dietary exposure underestimated in current risk assessments. This study examined the occurrence of nitrite, nitrate, and NAs in nine leafy green vegetables that were purchased from Danish supermarkets, pureed, and stored under varying conditions including ambient temperature, 5 °C, −20 °C and − 80 °C. Nitrite concentrations increased in most vegetables during ambient storage, with the highest concentration found in arugula after 48 h (2448 ± 213 mg·kg⁻¹). Simultaneously, nitrate levels decreased, indicating conversion to nitrite. The NAs N-nitrosodimethylamine (NDMA), N-nitrosopiperidine (NPIP), N-nitrosopyrrolidine (NPYR), N-nitrosomethylethylamine (NMEA), and N-nitrosomorpholine (NMOR) were detected in arugula, spinach, kale, cabbage, and lettuce under various conditions following pureeing. Among them, NPYR was found at the highest level in arugula after 72 h at ambient temperature, reaching 21.7 μg·kg⁻¹. These results emphasize the need to consider vegetables in NA exposure assessments, particularly those processed and stored under varied conditions. Future studies should include microbial, amine precursor or nitrate reductase expression data to provide further mechanistic insights into nitrite and NAs formation in leafy green vegetables.