Microstructure transitions derived from solubilization of lutein and lutein esters in food microemulsions.


Idit Amar, Abraham Aserin, and Nissim. Garti. 2004. “Microstructure transitions derived from solubilization of lutein and lutein esters in food microemulsions.” Colloids and Surfaces, B: Biointerfaces, 33, 3-4, Pp. 143–150.


Solubilization and structural transformations in nonionic food microemulsions, characterized by large continuous isotropic region, contg. solubilized lutein, and lutein ester were studied. The prepns. are of oil-based concs. composed of solubilized lutein or lutein ester in reverse micelles constructed from hydrophilic surfactant, alc. and R(+)-limonene. The reverse micelles are dild. along a 60/40 surfactant/oil diln. line with aq. phase (contg. water and glycerol) up to the opposite corner of the diagram where o/w microemulsions are formed passing through a bicontinuous phase, without any visual phase sepn. The diln. goes through two structural transitions that were detd. in empty (ref.) and solubilized systems. The solubilization capacity of both free lutein (FL) and lutein ester (LE) is considerably higher (as expected) in the reverse micelles (no aq. phase), and in the W/O microemulsions than in the O/W microemulsions, but the highest solubilization was obtained within the bicontinuous phase. The solubilization was found to be affected by the lipophilicity of the surfactant and is also concn.-dependent throughout all the microemulsions structures, but the most pronounced surfactant effect was shown to be in the bicontinuous region. Structural transitions w/o → bicontinuous occurred at 30% aq. phase in empty (ref.) microemulsions as well as in microemulsions contg. solubilized free and esterified lutein (at the max. solubilization levels). However, the transitions bicontinuous → o/w occurred at higher aq. phase contents of 50 and 60% aq. phase for FL and LE, resp., in comparison to a transition at 40% for the empty microemulsion. As a result, the bicontinuous region in the presence of the guest mols. becomes much broader. The results indicate that in the reverse swollen micelles the guest mols., being practically lipophilic will be easily accommodated at the concaved water interfaces (in the w/o region), which will enable high solubilization capacities, and without significant modifications of the interface. It becomes also evident that at zero curvature interfaces (bicontinuous) and in convex interfaces (oil/water) the lutein ester (the more lipophilic mol.) penetrates into the interface and swells both the bicontinuous interface and the droplets, similarly to most guest mols. However, free lutein is poorly accommodated at the interface and interferes with the interfacial organization and modifies the flattened curvature, affecting the transformation from bicontinuous to o/w droplets. [on SciFinder(R)]
Last updated on 05/27/2020