Is it okay to simmer green leafy vegetables for a long time?

　　Is it okay to simmer green leafy vegetables for a long time?

　　If green leafy vegetables are simmered for a long time during cooking, the nitrates in them will be converted into nitrites, which can easily cause food poisoning in consumers. At the same time, long-term stewing will also cause the loss of chlorophyll and vitamins in green leafy vegetables.

　　In addition, most quick-frozen vegetables have been processed and do not need to be cooked for too long, otherwise they will rot and lose a lot of nutrients.