Antioxidant capacity of 12 major isoflavones in soybean and their bioavailability under simulated digestion and human intestinal Caco-2 cells

Abstract Soy isoflavones (SIs) show various health benefits, such as antioxidant and estrogenic effects. It is important to understand bioaccessibility and bioavailability of SIs due to their close relationship with their bioactivities. In this study, antioxidant capacity, bioaccessibility, and bioavailability of twelve SIs were evaluated using radical-scavenging methods, a simulation of the human digestion, and Caco-2 cell in Transwell, respectively. All SIs were stable (91.1–99.2%) under gastric digestion compared with the control (100%), whereas acetyl and malonyl conjugates were unstable (38.5% and 65.5%, respectively) under small intestinal digestion. SI aglycones showed higher permeation (7–15 times) and cell accumulation (8.8 times) than their glucosides. A small amount of SI conjugates was found in their intact forms in the cell and in the basolateral side of the Transwell. These results suggest that SI conjugates, especially malonyl and acetyl forms, have incidental bioactivity after being metabolized to aglycones inside the cell.