Tannin, snail, refers to water-soluble polyphenol compound Lti with molecular weight of 500-3000, which can precipitate protein and biodegrade. The application is extended to medicine, food and other fields, including related low molecular weight polyphenols. Tannin is widely found in Chinese herbal medicines (such as five times, pomegranate peel and agrimony) and plant foods (cereal beans such as barley, sorghum and mung beans, and fruits and vegetables such as onions, grapes and tea). Tannin will form a precipitation complex with protein, vitamins, minerals, etc., which is regarded as an anti-nutritional substance and will reduce the product quality due to bacterial or non-bacterial oxidative browning. The astringency produced by the association of tannin with saliva protein is also a suitable flavor L3J, such as tea, red wine, persimmon, plum, immature banana, etc., which contains a proper amount of tannin and has a unique flavor. In medicine, tannins can stop bleeding, heal wounds, inhibit bacteria and resist allergy, especially have the functions of antioxidation, anticancer and prevention of cardiovascular and cerebrovascular diseases, and have become the research focus of phenolic compounds in recent years.