Vitamin B2 has "three fears".
Fear of water: Vitamin B2 is a water-soluble vitamin, so it is lost with water. For example, washing rice will wash away a significant amount of Vitamin B2. Additionally, in the popular "lao fan" (rice scooped out of boiling water) eaten in many places, only about 50% of the Vitamin B2 is retained.
Fear of light: Vitamin B2 is very sensitive to light, especially ultraviolet light. Milk contains Vitamin B2, which is why the milk cartons we usually buy have a black inner lining—to protect it from light. Therefore, milk sold in transparent glass bottles will lose its Vitamin B2 and should be avoided.
Fear of alkali: Alkali is the enemy of most vitamins, and Vitamin B2 is no exception. Therefore, it is not recommended to add alkali when cooking congee or blanching green vegetables.
Furthermore, Vitamin B2 is not particularly abundant in fresh vegetables, meat, eggs, or dairy. Therefore, the best way to prevent a Vitamin B2 deficiency is to have a rational and balanced diet, and pay attention to the "three fears" mentioned above when purchasing and cooking.