Phase behavior of bile acid/lipid/water systems containing model dietary lipids

Dietary lipids are solubilized in bile acid micelles in the small intestine. In the present study, we investigate the phase behavior of bile acid/model rapeseed oil (or model beef tallow)/water systems to predict interfacial phenomena during consumption of a variety of foods. The structures of molecular assemblies are identified based on polarizing microscope images, wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). The results of in vitro tests suggest that an increase in the intake of model rapeseed oil causes the formation of multi-lamellar vesicles and lamellar liquid crystals. The molecules in the lamellar liquid crystal are formed highly ordered layer structure with the spacing of 8.8 nm along the c-axis, while monoclinic packed structure is constructed as two-dimensional structure in ab-plane due to bulky molecular structures of bile acid and unsaturated fatty acid. When the model beef tallow composition in the model system is more than several wt.%, stearic acid crystals are extracted. Moreover, bicarbonate ions are important ingredients to solubilize >10 wt.% of the model lipids. These phase transitions might be induced by the addition of dietary lipids in vivo during the consumption of oil or meat. Our findings are significant for understanding the lipid absorption process in the small intestine, and for developing medical and healthcare products.