Summary: Green vegetables contain chlorophyll, when chlorophyll is cooked, it produces carbon dioxide. Since you have to cover the vegetables to steam them, the chlorophyll turns a drab, grayish color. You can prevent this by boiling the greens, in salted ... (怎樣炒菜才使青菜保持青綠？一般來說，綠色蔬菜應該在低溫環境保存，如果溫度超過高，所含的「葉綠素酶」會將葉綠素與蛋白質分開而散失，但如果低於零度，葉綠素又會因冷凍而遭到破壞。)
