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Background and Objectives: More than 80% of human dietary intake of nitrate comes from vegetables. Nitrate is converted to nitrite and nitrosacids, which can combine with primary and secondary amines, producing nitrosamines. Nitrosamines have hazardous effects on human health. Based on the results of the last National Food Consumption Survey in Iran (2002), lettuce, tomatoes and potatoes are the most widely consumed green leafy, fruit-bearing and tuberous vegetables. This study was carried out to determine the nitrate contents of these 3 vegetables on sale in the Tehran Central Fruit and Vegetable Market. Materials and Methods: Three-Kg samples of lettuce, tomatoes, and potatoes, distributed in Tehran (Tehran Central Market, the Main Fruit, Vegetable and Agricultural Products Market) were taken during summer and winter 2007, at least 25 samples of each vegetable (a total of 157 samples). After separating inedible portions, the samples were washed, rinsed, minced, mixed thoroughly, freeze-dried and stored at -18◦C until analyzed. Nitrate was determined in the samples using HPLC based on the EC 12014-2 method, and Mann-Whitney nonparametric test, Kruskal-Wallis ANOVA and Bon-Ferroni multiple comparison were used for statistical analysis of the data. Results: The mean concentration of nitrate in lettuce, tomatoes, and potatoes was 1123.46, 155.65, and 188.41 ppm, respectively. It is seen that the nitrate content of leafy vegetables was the highest, followed by fruit-bearing and tuberous vegetables. Nitrate accumulation in summer lettuce (1223.57 ppm) was higher than in the winter sample (1046.82 ppm), but in the case of tomatoes and potatoes it was the other way round: 210.25 and 264.64 ppm in winter and 101.11 and 104.45 ppm in summer, respectively. The average nitrate contents of lettuce in both seasons were within the internationally permitted range, while in the case of winter potatoes and tomatoes the averages exceeded the respective permitted ranges. Conclusion: Nitrate accumulation in vegetables can vary according to the harvesting season. Further research is recommended to determine the effects of such factors as variety, age, agricultural practices and storage conditions. Keywords: Lettuce, Tomatoes, Potatoes, Nitrate, Nitrite

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Background and objective: Vegetables is one of the most important expose sources of nitrite and nitrate in human's diet. The aim of this study is evaluation of boiling and freezing process on nitrite and nitrate levels in commonly consumed vegetables. Materials and methods: It was the descriptive – analyzed study. 180 vegetable samples were taken from Kermanshah markets, randomly. Nitrite and nitrate concentration was determined by Greece- Ilosoay method. Then, freezing and boiling process were carried out on samples and again, nitrite and nitrate levels were measurement. The mean differences were analyzed by using ANOVA and SPSS program. Results: The amounts of nitrite and nitrate in many samples had significant differences (p<0.05), depending on type of process and product. Increase in time of freeze storage from 1 to 3 month resulted in increase in amounts of nitrate and nitrite in many samples while, 9 month freezing storage decreased nitrate and nitrite levels. Boiling process increased nitrate and nitrite levels in several vegetables, such as scallion and decreased it for instance, in garlic chives Conclusion: Long term freezing process is a suitable method to reduce nitrate and nitrite levels in vegetables. Regarding to daily consume of vegetables and its positive effects on public health, quality control of this product and studying the other food processing is very important. Keywords: Boiling, Freezing, Nitrate, Nitrite, Vegetables