Vitamin B 12 is mainly contained in animal proteins, such as liver, kidney, meat, dairy products, fish, shellfish and eggs. Most plant foods do not contain vitamin B 12, and only soybeans contain vitamin B 12. For example, fermented soybean products used by people in Sichuan Province, Douchi, can provide vitamin B 12. Vitamin B 12 is stable in neutral and weakly acidic environments, and can be slowly decomposed in alkaline and strong acid environments. It is unstable in the presence of vitamin C. Milk loses 7% after pasteurization and 30% of vitamin B 12 after boiling for 2 ~ 3 minutes. Therefore, the sterilized milk sold in the market should be heated for a short time and should not be boiled for too long.