STRUCTURAL STUDIES OF COMMERCIAL FAT EMULSIONS USED IN PARENTERAL-NUTRITION

In this paper, we demonstrate that by employing a combination of sedim entation field-flow fractionation (sedFFF) and other characterization techniques, such as photon correlation spectroscopy (PCS) and freeze-f racture electron microscopy (EM), it is possible to show that commerci al fat emulsions of similar overall chemical compositions not only may exhibit different size distributions but may have different densities as well. A closer look at the density difference between droplet and suspension medium, on the one hand, and the droplet size, on the other , demonstrates that fat emulsions may have structures other than the t raditional oil droplet surrounded by a monolayer of surfactant. From o ur determined and simulated density differences, we propose that these emulsion droplets may have a multilayered surfactant arrangement as w ell as an inclusion of water vesicles in the oil phase of the emulsion . Freeze-fracture EM observations provide evidence to confirm the exis tence of such complex structures. These findings are supported by rece nt EM work from other laboratories, as well as through chemical verifi cation of elevated water contents in the oil droplets of these emulsio ns.