Abstract: Tannins are water-soluble polyphenolic secondary metabolites of higher plants with the molar mass from 300 to 3000. Hydrolysable and condensed tannins are the two major classes of tannins. There are two groups of hydrolysable tannins:gallotannins and ellagitannins on the basis of structural characteristics. In nature, some microbes are resistant to tannins, even capable of degrading tannins into low-molar-mass tannins and lots of derivatives which have marked biological and pharmacological activities. Gallotannins can be degraded more easily than ellagitannins which have complicated structures with the further coupling C—C bond. However, some bacteria and fungi from the ellagitannin-rich soil, leaves and tannery liquors can hydrolyze ellagitannins. Because of the complicated structures of the further coupling C—C bonds, both complex tannins and condensed tannins are harder to be degraded than gallotannins and ellagitannins in both aerobic and anaerobic environments. This review could provide much references for the further researches on biodegradation of tannins.

Key words: hydrolysable tannins, degradation, microorganisms