Physico-chemical stability and structural characterization of thickened multilamellar beta-carotene-loaded liposome dispersions produced using a proliposome method
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The objective of this study was to investigate in more detail the structure of multilamellar beta-carotene-loaded liposome dispersions produced by proliposome hydration. Such dispersions were stabilized using xanthan gum as a thickener in different concentrations, and their stabilities were monitored for 90 days. The vesicles exhibited an average diameter in the range of 700 to 3000 nm, and the liposomes were capable of protecting β-carotene from degradation for a period of 90 days. The dispersions were also characterized by transmission electron microscopy, differential scanning calorimetry, rheology, and small-angle X-ray scattering (SAXS). The thermal analyses showed that neither the β-carotene nor the xanthan gum affected the liposome bilayer structure. The presence of the xanthan gum, which affects the scattering intensity, was not an obstacle to obtain the structural parameters by SAXS modeling, as a modified modeling strategy (Gaussian deconvolution) was applied. This modeling resulted in 40 symmetric layers, and the results obtained with the variation of temperature were in agreement with the gel-liquid crystalline transition temperature obtained by calorimetric measurements. Additionally, the rheological data showed that xanthan gum was not as effective as a mixture of xanthan gum and guar gum at stabilizing the liposomes, most likely due to the higher stiffness of the gum alone compared with that of its combination with guar gum.
KeywordsProliposomes Beta-carotene Microencapsulation Multilamellar liposomes SAXS
The authors are grateful to FAPESP for the financial support (project 2009/01087-7) and the scholarships awarded (projects 2009/14868-7, 2011/01277-0, and 2011/03901-3). The authors also thank Danisco for the donation of xanthan gum and Carlos Alberto Paula Leite for the micrographs of the liposomes.
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