The distribution of hydrophobic solutes, such as flavors, bioactive compounds and drug molecules within product matrices impacts pharmaceuticals, agrochemicals, consumer products including food, as well as the environment. The solutes' preferential partitioning into the non-polar parts of the sample matrix affects their stability, release to the vapour phase, and the methods needed for their incorporation. Therefore, determining the local distribution of solutes and the factors that affect their release is important in order to design products with improved efficacy and quality. Colloidal assemblies of phospholipids are of particular interest, as they comprise safe, widespread natural amphiphiles with the ability to solubilize hydrophobic compounds. However, there is a lack of accurate and non-destructive methods to study the local distribution of solutes between the sample matrix elements, the aqueous phase, and the vapour phase, making it difficult to assess the effect of structure on stability and release. Short time headspace microextraction allows us to determine the local distribution of hydrophobic solutes and the effect of colloidal structure while keeping the system intact. Using thermodynamic relationships, the detected concentrations of compounds in the vapour phase could be used to determine local properties within the sample matrix. The colloids of focus in this study, phosphatidylcholine vesicles, were shown to be very effective at solubilizing hydrophobic molecules, yielding vesicle-water partition coefficients of ~10<sup>4</sup>M<sup>–1</sup>. These results extend our previous work on micellar solutions by developing a quantification method for the solubilization and retention of volatile nonpolar compounds in vesicles. The local partitioning of the aroma molecule, limonene, was investigated in vesicles of various structures, lipid composition, and at different temperatures. Vesicles were found to be much more effective at solubilizing limonene than short-chain phosphatidylcholine micelles. In addition, changes in the structure of the lipid bilayer, including phospholipid saturation and fluidity, changes the partitioning properties of limonene.

Local distribution of limonene in phospholipid vesicles

ACS Fall 2021

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