Nitrite is converted from nitrate, so the content of nitrate in vegetables is closely related to the content of nitrite. The nitrate added by plants due to the absorption of nitrogen-containing fertilizers (nitrogen fertilizers) is mainly concentrated in the young tissues of plants, and the mature seeds are nitrate-free, because in the middle and late stages of plant growth, inorganic nitrogen (such as nitric acid) Salt) is converted into organic nitrogen such as protein and nucleic acid, and stored in seeds. The survey found that about 80% of the nitrate and nitrite in the diet came from vegetables, and the remaining 20% came from drinking water and other foods. Where the edible part is the vegetable vegetative organs (leaves, stems, roots) vegetables, such as spinach, celery, cabbage, radish, lettuce, etc., the nitrate content is relatively high, while the edible part is the plant propagation organs (flowers, fruits, Seeds) vegetables, such as cauliflower, cucumber, eggplant, green pepper, bean pods, etc., have low nitrate content.

In addition to the types of vegetables, there are the following factors that increase the nitrite content in vegetables:

　　①Pickled? Pickled vegetables, mainly short-term pickled vegetables contain more Nitrite. When the marinating conditions are bad or the marinating time is too long, the * nitrite content will increase greatly when it deteriorates or becomes moldy. In the process of pickling vegetables, within 4 hours of soaking, the content of nitrite is minimal. After that, nitrate will be transformed into harmful nitrite by some bacteria, and it will reach a peak soon (3 to 14 days). Nitrate is gradually used by bacteria or broken down into other nitrogen-containing substances. (After 30 days) The nitrite in pickled vegetables will gradually drop to a lower level, or even disappear. Therefore, vegetables that have been marinated for more than one month have lower nitrite.

　　 Therefore, when pickling vegetables, pickle them thoroughly before eating, and avoid moldy. In addition, when pickling vegetables, adding onion, ginger, garlic, and chili juice will help reduce the content of nitrite. Vitamin C can also block the synthesis of carcinogen nitrosamines from nitrite.

　　In general, foods such as kimchi, which are produced according to scientific processes, have sufficient curing time, and are free of moldy mildew, are safe. It is important to know that compared to fresh products, pickled vegetables have a greater loss of nutrients and salt content is too high. From a nutritional point of view, it is far better to eat fresh vegetables, so the "Chinese Dietary Guidelines 2007" recommends that pickled Eat less vegetables and pickles.

　　② Long-term storage? Among fresh vegetables just harvested, the nitrite content is very low, but under the action of its own enzyme, the nitrite content will gradually increase as the storage time is extended. Vegetables are stored at room temperature for 1 to 3 days, and the peak of nitrite is reached; under cold storage conditions, the peak is reached in 3 to 5 days. For green leafy vegetables such as spinach and pakchoi, the amount of nitrite produced is particularly large, and the effect of refrigerator storage is far better than that of room temperature storage; for cucumbers and potatoes, the difference is not obvious. However, after storing Chinese cabbage for many days, the nitrate and nitrite content in it has decreased, which may be due to nutrient loss and conversion to other nitrogen-containing substances during storage, so you do not have to worry about the nitrite of Chinese cabbage stored in winter Salt problems. After the vegetables* are spoiled, the nitrite content will increase greatly under the action of bacteria, and they should be avoided.

　　Vegetables are expensive, and when conditions permit, try not to eat vegetables that have been stored for too long, are not fresh, or have begun to deteriorate.

　　③Leftovers (referring to uneaten vegetable dishes? After the vegetables are cooked, their own enzymes are killed, but the bacteria multiply in large numbers, and many bacteria can produce nitrate reductase, thus Converting nitrate to nitrite increases the content of nitrite in leftovers.

　　Storing leftovers in the refrigerator at low temperature is a good way to inhibit the reproduction of bacteria and reduce the production of nitrite. However, it must be put in the refrigerator when the vegetables have just been cooked and the number of bacteria is still very low. If the dishes have been turned on the plate with chopsticks for a period of time, it has caused a lot of bacteria to multiply, even if it is put in the refrigerator, it is not safe. Room temperature The longer the storage time, the more the number of flips, the more bacteria will multiply. Reheating the leftovers before eating can kill the bacteria and avoid bacterial food poisoning, but it still cannot destroy the nitrite. Therefore, even if it is put in the refrigerator Refrigerate, the leftovers should not be stored for more than 4 to 6 hours. Leftovers that exceed this storage time should not be eaten.