Choosing appropriate methods and standards for assaying tannin.

Tannins are chemically diverse polyphenolics that have multiple biological activities. Attempts to establish the ecological significance of tannins have been hindered by the complexities of tannin analysis. A multitude of analytical procedures for tannins has been described, but it is difficult for the nonspecialist to select appropriate methods. We have classified the most common procedures for determining tannin as either chemical assays, appropriate for determining the amount and the chemical nature of the tannin in a sample, or as protein-binding assays, suitable for determining the potential biological activity of the tannin in a sample. We have recommended procedures that are particularly reliable and straightforward for general use. We have also considered the problems encountered in selecting appropriate standards for tannin analysis and have recommended standards that are readily available.