Effects of freezing vegetables on nitrate content and their health-related risk

Vegetables are the major source of nitrate entry into the human body. The present study was conducted to investigate the influence of freezing on nitrate content in 15 species of vegetables from three commonly used groups: leafy, root and fruit vegetables. Determination of nitrate ions in sample extracts was performed using ion chromatography. The highest level of nitrate content before freezing was determined in samples of radish, while the lowest content of nitrate in raw vegetables was determined in samples of pepper. In raw samples of leafy celery and cucumber, nitrates were not detected. Results obtained by analyzing samples after freezing showed that this process has a different influence on the investigated samples. Some samples contained a higher level of nitrate after freezing, while others contained less. Part of the investigated vegetables showed an increased health risk if consumed in an amount of 400 g per day.