Effect of fatty acids on self-assembly of soybean lecithin systems.
With the increasing interest in natural formulations for drug administration and functional foods, it is desirable a good knowledge of the phase behavior of lecithin/fatty acid formulations. Phase structure and properties of ternary lecithin/fatty acids/water systems are studied at 37°C, making emphasis in regions with relatively low water and fatty acid content. The effect of fatty acid saturation degree on the phase microstructure is studied by comparing a fully saturated (palmitic acid, C16:0), monounsaturated (oleic acid, C18:1), and diunsaturated (linoleic acid, C18:2) fatty acids. Phase determinations are based on a combination of polarized light microscopy and small-angle X-ray scattering measurements. Interestingly, unsaturated (oleic acid and linoleic acid) fatty acid destabilizes the lamellar bilayer. Slight differences are observed between the phase diagrams produced by the unsaturated ones: small lamellar, medium cubic and large hexagonal regions. A narrow isotropic fluid region also appears on the lecithin-fatty acid axis, up to 8wt% water. In contrast, a marked difference in phase microsctructure was observed between unsaturated and saturated systems in which the cubic and isotropic fluid phases are not formed. These differences are, probably, a consequence of the high Krafft point of the C16 saturated chains that imply rather rigid chains. However, unsaturated fatty acids result in more flexible tails. The frequent presence of, at least, one unsaturated chain in phospholipids makes it very likely a better mixing situation than in the case of more rigid chains. This swelling potential favors the formation of reverse hexagonal, cubic, and micellar phases. Both unsaturated fatty acid systems evolve by aging, with a reduction of the extension of reverse hexagonal phase and migration of the cubic phase to lower fatty acid and water contents. The kinetic stability of the systems seems to be controlled by the unsaturation of fatty acids.
Departamento de Ingeniería de los procesos Agroalimentarios y Biotecnológicos (GIPAB), Universidad del Valle, A.A. 25360 Cali, Colombia.
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Godoy
Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, Faculty of Pharmacy, University of Alcalá, Ctra. Madrid-Barcelona Km 33.6, E-28871 Alcalá de Henares, Madrid, Spain.
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Valiente
Department de Tecnologia Química i de Tensioactius, Institut de Química Avançada de Catalunya, IQAC-CSIC, E-08034 Barcelona, Spain.
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Department of Analytical Chemistry, Physical Chemistry and Chemical Engineering, Faculty of Pharmacy, University of Alcalá, Ctra. Madrid-Barcelona Km 33.6, E-28871 Alcalá de Henares, Madrid, Spain; University Institute of Research in Police Sciences (IUICP), University of Alcalá, Ctra. Madrid-Barcelona Km 33.6, E-28871 Alcalá de Henares, Madrid, Spain. Electronic address: gemma.montalvo@uah.es.
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Montalvo
D005227:Fatty Acids / Q000737:chemistry*; D005231:Fatty Acids, Unsaturated / Q000737:chemistry; D007700:Kinetics; D054709:Lecithins / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008859:Microscopy, Polarization; D053838:Scattering, Small Angle; D013025:Glycine max / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
D005227:Fatty Acids; D005231:Fatty Acids, Unsaturated; D054709:Lecithins; D008051:Lipid Bilayers; D014867:Water
Fatty acids; Linoleic acid; Oleic acid; Palmitic acid; Small-angle X-ray scattering; Soybean lecithin