Microemulsions Based on Soybean Phosphatidylcholine and Triglycerides. Phase Behavior and Microstructure

Abstract

We have studied the phase behavior and microstructure of water/1-propanol/soybean phosphatidylcholine (SbPC)/triglyceride systems. Microemulsions are formed with both medium-chain triglycerides (MCT) and long-chain triglycerides. The amount of SbPC and 1-propanol needed to form a microemulsion increases as the chain length of the triglyceride increases. The MCT system was investigated in more detail and compared with a hexadecane system. The phase behavior and pulsed field gradient NMR data for the MCT system suggest that the microemulsions formed at low SbPC concentrations and 0 < α < 0.5, where α is defined as the weight fraction of oil/(oil + water), are of a bicontinuous type. The self-diffusion data for the microemulsions formed at higher SbPC concentrations clearly indicate that there is some structure also in these microemulsions with an oil-in-water droplet structure at the water rich side and a gradual change to a bicontinuous structure when the MCT concentration is increased. The bicontinuity appears to be preserved even at low water concentrations. The microstructure of the microemulsion in this part of the phase diagram is, however, less well-defined, most probably with large polydispersity and rapid fusion and fission of the oil and water domains. The hydrodynamic radius and aggregation number of the SbPC aggregates formed in a mixture of 22.5 wt % SbPC, 22.5 wt % 1-propanol, and 55 wt % water was calculated as 27.5 Å and 68 SbPC molecules/aggregate, respectively.