Tannins are water-soluble polyphenolic secondary metabolites of higher plants with the molar 4 mass from 300 to 3000.Hydrolysable and condensed tannins are the two major classes of tannins.

• 摘要单宁为高等植物的次生代谢产物，是相对分子质量为300到3000的多酚类化合物，主要分为水解单宁和缩合单宁两大类。