Tannins: thermostable pigments which complex dietary proteins and inhibit digestive enzymes

The presence of antinutritional factors in legume seeds and other vegetables has been considered as an expression of the chemical warfare of plants against their predators. As a consequence, the nutritional utilization of these foods has only been possible through the use of a variety of treatments (cooking, fermentation, germination) which increase nutrient bioavailability. Nonetheless, some factors are not destroyed by effect of seed processing, among which stand a family of polymeric polyphenols called tannins. These pigments have the ability to complex and precipitate proteins and inhibit digestive enzymes. This paper describes what has been accomplished in regards to the selection of an appropriate solvent to extract bean polyphenols, the assessment of the most commonly used assay procedures, the purification of bean tannins and the evaluation of their interaction with proteins and digestive enzymes, responsible for their antinutritional effect.