Modification of condensed tannins: from polyphenol chemistry to materials engineering

Abstract

Condensed tannins (CTs) are high molar mass polyphenolic bio-polymers based on flavonol units. CTs have been well-studied due to their respective biological activity. However, the application of CTs in several areas is limited because of their physicochemical properties. The objective of this review is to investigate the state of the art regarding the chemical modification of CTs, and to outline recent and potential applications of tannin derivatives. An overview of the most important reactions is given, and a comprehensive summary of the experimental parameters for modification (chemicals, time, temperature, solvent type, and yield) is presented. The impact of the modification on the physicochemical properties of derivatives in comparison to native tannin behavior is discussed. Finally, the applicability of modified or unmodified CTs is described, referring to academic articles and patents. Future research in terms of modification reaction type, as well as derivatizing agents, is discussed.