2. Lotus root slices, potatoes or yam with cut roots turn brown in the blink of an eye, which is caused by its rich phenol oxidase. It can be solved by scalding 10 second, which not only "kills" the enzyme, but also does not affect the taste.
3. Beans such as kidney beans and broad beans are also easy to change color when entering the dish, and can be "oiled" in advance. Frying beans with oil or oil before frying can keep them green better than blanching them with water. Due to the high temperature and certain viscosity of oil, a dense oil film can be formed on the surface of beans, reducing the oxidative discoloration loss of green substances.
4. Onions Onions contain a substance called flavonoids. When flavonoids meet metals such as iron and aluminum, they will produce compounds such as brown, blue and black, which will make the color of onions opaque. The best solution is to dip the chopped onion in some dry flour and stir it evenly before frying, so as to avoid the direct contact between flavonoids and iron and aluminum, and the onion will not change color and taste more crisp and tender.
Purple cabbage will turn blue when cooking. The natural anthocyanin in purple cabbage is blue-purple under neutral conditions, but it will turn blue under alkaline conditions. Therefore, the treatment method should be just the opposite of green vegetables. It is necessary to create acidic conditions. Covering the lid helps to keep the color. Add a little vinegar, and the color of purple cabbage will be brighter.