the effect of home cooking method and refrigeration processes on the level of nitrate and nitrite in spinach

background: spinach is one of the vegetables with a high concentration of nitrate which is affected by various processes such as cooking and refrigeration before consumption. the present study aimed to investigate the effect of home cooking method, which has not been studied before, on the level of nitrate and nitrite in spinach. the effect of refrigeration was studied, as well.   methods: after removing non-edible parts of spinach, it was cut into 4-7 cm pieces. then, it was washed with deionized water thrice and drained. a part of raw spinach was set aside to measure the nitrate and nitrite and the other part was heated in a closed container without adding water, until almost all the water of the spinach was evaporated and then refrigerated. hplc method was used to measure the nitrite and nitrate levels. the collected data were analyzed using wilcoxon test by spss.   results: the mean concentrations of nitrate and nitrite in the raw spinach were 336.54±182.2 and 26.49±10.07 mg/kg, respectively. cooking process caused a significant increase in the level of nitrate, while refrigeration process led to a significant decrease in this regard. besides, a slight reduction was observed in the nitrite level after cooking, but the change was not statistically significant. refrigeration also had no significant effects on the nitrite level of spinach.   conclusion: considering the non-significant changes in nitrite levels, it seems that home cooking without adding water, unlike refrigeration, is not a proper method to reduce the intake of nitrates and nitrites from spinach.