Transitions in the internal structure of lipid droplets during fat digestion

Abstract

This work focuses on colloidal transformations during the digestion of dietary triglyceride-lipids under physiological conditions present in the intestine. In vitrodigestion experiments with triglyceride emulsions and pancreatic lipase are monitored by time-resolved small-angle X-ray scattering, polarized and depolarized dynamic light scattering and cryogenic transmission electron microscopy as complementary methods. In the intestine, the interface-active pancreatic lipase–colipase complex adsorbs to the interface of the emulsified lipids and quantitatively hydrolyses the tri- and diglyceride to 2-monoglycerides and fatty acids as the final digestion products. Both products are amphiphilic under intestinal conditions and form a great variety of self-assembled structures, depending on composition and pH. With time of lipase action, the interior of the emulsion particles was found to self-assemble to oil continuous structures with increasing hydrophilicity of the interface. A transition from oil emulsion to emulsified microemulsion, micellar cubic, inverse hexagonal, and bicontinuous cubic liquid-crystalline droplets was found. Self-assembled structures formed during the in vitro lipid digestion process were investigated as a function of bile-juice concentration, pH and hydrophobic additives. Significant differences in structure formation and transition times (kinetics) could be observed when varying these crucial parameters. Vesicles were found to be the dominating final structures of the triglyceride digestion process.