Effects of some processing methods on nitrate and nitrite changes in cruciferous vegetables

Changes in nitrate and nitrite content in selected cruciferous vegetables, resulting from blanching, boiling, freezing, frozen storage and boiling after previous freezing, were analyzed. The highest level of nitrate was detected in curly kale (302.0 mg/kg) and the lowest in green cauliflower (61.0 mg/kg). As for nitrite, the respective levels were found in white cauliflower (3.49 mg/kg) and green cauliflower (1.47 mg/kg). Both blanching and boiling of the cruciferous vegetables caused a considerable decrease in the total nitrate content, but at the same time no explicit changes were noted regarding the level of nitrite. In the vegetables stored frozen for 48 h, previously blanched, either an increase or no change was observed in the nitrate level, with the changes in the nitrite level being irregular. In the vegetables stored frozen for 4 months, previously blanched, generally a decrease was noted in the nitrate, and an increase in the nitrite level compared to the levels in the blanched vegetables. Boiling of the frozen vegetables (stored frozen for 48 h) most frequently caused a considerable reduction of the nitrate level in comparison to the content in the raw frozen vegetables. No changes were observed resulting from the boiling of the vegetables previously stored frozen for 4 months. Simultaneously, no explicit changes were found regarding the nitrite level in the frozen vegetable after boiling.