Iron, Catechin, and Ferulic Acid Inhibit Cellular Uptake of β-Carotene by Reducing Micellization

Green leafy vegetables have low beta-carotene bioavailability, which we hypothesized to be, at least in part, due to high contents of fiber, minerals, and phenolics. We investigated the effects of pectin (40-120 mu g/mL), iron (50-150 mu g/mL), ferulic acid (30-90 mu g/mL), and catechin (50-150 mu g/mL), in a model system, on beta-carotene micellization (in vitro digestion) and intestinal absorption (Caco-2 cell model). Iron, pectin, ferulic acid, and catechin on average reduced (p < 0.05) beta-carotene micellization (1.49 +/- 0.05 mu mol/L) by 66.9, 59.3, 43.2, and 51.7%, respectively. Iron reduced micellization by precipitating bile salts from solution and ferulic acid and catechin by inhibition of pancreatic lipase. beta-Carotene uptake by Caco-2 cells (2.63 +/- 0.22%) was reduced (p < 0.05) by 37.4, 70.1, 77.0, and 75.1%, respectively, when it was digested with pectin, iron, ferulic acid, or catechin. However, when individual test compounds were added to already micellized beta-carotene, they did not inhibit beta-carotene uptake. The large reductions in beta-carotene micellization observed in vitro warrant further investigation in humans using model green leafy vegetable systems to elucidate their relevance under real-life conditions.