The result of oxidative polymerization of phenolic substances in mung bean skin under the action of oxygen in the air.

Mung bean soup "locks color":

1. Clean the mung beans and soak them for 2 hours. Do not discard the soaking water, because after long soaking, the mung bean skin will lose its color. Polyphenols will be dissolved in large amounts in the bean soaking water.

2. Add a few drops of lemon juice when cooking mung bean soup.

3. When cooking mung bean soup, do not add alkali in order to make it softer. Adding alkali will not only make the mung bean soup turn red, but will also lose vitamin B and reduce antioxidant activity.

4. Cover the lid when cooking mung bean soup. This will prevent the mung beans from being exposed to oxygen and reduce oxidation and reddening. After cooking, don't be in a hurry to open the lid, keep it covered and let it cool before drinking. In addition, there is another point that everyone should pay attention to, that is, the cooking time should not be too long. It is recommended to control it within no more than 1.2 hours. Cooking for too long will cause the content of flavonoids to decrease.