ABSTRACT
Tannins have played a pivotal role in human evolution. This chapter focuses on the structural characteristics, analytical methods, and sources of tannins and their effects on major metabolic diseases. Tannins are ubiquitous with extremely high diversity, resulting in complex classification sometimes based on their biological effects differentiated by solubility/absorptivity or chemical structure. The structural diversity of tannins enables strong interactions depending on their polyphenolic structures with different compounds, including but not limited to proteins, carbohydrates, polysaccharides, lipids, and metals. The protein precipitation method is used sometimes to evaluate the biological activity of tannins and the nutritional value of tannin containing foods. The Folin reaction, based on phosphomolybdic acid reduction by phenols in aqueous alkali, has been recommended for tannin analysis in wines and distilled beverages. Tannins are generally believed to be limited to a few cereals, particularly the so-called pseudocereals such as sorghum tannin, which has been extensively investigated.
