Xu Jiafen introduced that raw cabbage contains non-toxic nitrate, which will produce nitrite after cooking. The longer it is left, the higher the nitrite content. When nitrite enters the human body, it will be converted into nitrosamine, which is a carcinogen.
Xu Jiafen suggested that Chinese cabbage should be washed and cut, cooked after cutting, and eaten when cooked. And every time you cook Chinese cabbage, you should try to cook as much as you can, preferably without leftovers. If the leftovers are unavoidable and unwilling to be dumped, you can eat some foods that inhibit the formation of nitrosamines, such as garlic. Because allicin can inhibit nitrate-reducing bacteria, it can reduce nitrite in the stomach. Or drink some tea after meals, because tea polyphenols in tea can block the formation of nitrosamines.
Extended data:
"Overnight food" has nothing to do with "night"
From the perspective of food science, staying overnight is not a problem. The essence of the problem is what happens to cooked vegetables during storage. We are worried that nitrate in vegetables will be converted into nitrite. This transformation process can be realized by the original reductases in vegetables, but in the process of cooking, these enzymes lose their activity and this road is cut off.
Another way is the role of bacteria. Originally, the vegetables were cooked and the bacteria in them were almost killed. But in the process of eating, some bacteria will enter the leftovers on chopsticks; During the preservation process, some bacteria in the air may also enter. Cooked vegetables are more suitable for bacterial growth. Under appropriate conditions, they will grow in large quantities, and nitrate may be converted into nitrite during the growth process.
This process has nothing to do with the overnight interval, but only with the preservation conditions. Finally, how much nitrite will be produced in vegetables depends on the vegetables themselves; Secondly, under what conditions are cooked vegetables preserved; The third is how long it has been preserved.
It can be seen that "overnight dishes" may indeed produce carcinogen nitrite. If we put the vegetables we bought overnight before cooking and overnight after cooking, the result is that nitrite may be produced whether the vegetables are cooked or cooked the next day. Once produced, it cannot be removed.
Baidu encyclopedia-overnight dishes