Analysis of condensed tannins: a review

Plant condensed tannins (proanthocyanidins, PAs) have both positive and negative effects on feed digestibility and animal performance, depending both on the quantity and biological activity of the tannins that are present. In this review, the chemistry and analysis of condensed tannins (PAs) are examined. Our first focus is on the complexity of the structures of condensed tannins and our second emphasis is on the analytical methods used to evaluate tannins. The section on methods is subdivided into a discussion of methods to determine the amount of condensed tannins or total phenolics in a sample and a section on methods to measure biological activity. The methods to measure reactivity include assays involving protein binding and precipitation, as well as those that involve enzymatic and microbial inhibition. The last section of the paper discusses structure–activity relationships and provides information on how to select appropriate assays for measurement of the quantity and activity of condensed tannins.