Effect of some processing methods on nitrate changes in different vegetables

This study reports the levels of nitrate of four commonly consumed fresh vegetable samples, (onion, potato, carrot and tomato), from markets in Isfahan, center of Iran. Nitrate levels ranged between 34.67 and 198.09 mg kg−1. The maximum residue levels established for nitrate in carrot followed by, onion, potato and tomato. The effects of various cooking (traditional boiling, boiling in microwave system and frying) methods on nitrate-N contents in vegetables have also been studied. The study showed that the nitrate content of traditional boiling reduces nitrate content by 38.79–74.03 %. Lower reduction of the nitrate level, compared to traditional boiling vegetables, resulted from boiling in microwave system. The frying in soya bean oil elevated nitrate contents from 81.33 to 159.10 %. A comparison of the nitrate obtained by standardized method and the nitrate contents in vegetables of other countries are also presented.