The gastrointestinal behavior of saponins and its significance for their bioavailability and bioactivities

Saponins are bioactive compounds of increasing interest. The events that take place during digestion are highly related to their bioactivities, because saponins are poorly absorbed and have a long residence time in the intestinal tract. The poor bioavailability of saponins is explained by a sum of factors, but the more favorable properties of sapogenins result in higher bioavailability and bioactivity. The gastric and colonic transformations of saponins are relevant in the release of sapogenins. Saponins inhibit enzymes and cholesterol absorption, but specific chemical structures of saponins are relevant for an efficient activity. Finally, the recent research has pointed to saponins as prebiotic-like compounds. This review summarizes the current knowledge on the events that take place during digestion of saponins and sapogenins related to their bioactivities, with special emphasis on the factors that modulate their bioavailability, bioaccessibility, inhibition of digestive enzymes and cholesterol absorption, and the importance of the microbiota-saponins relationship.