Entrapment and delivery of α-tocopherol by a self-assembled, alginate-conjugated prodrug nanostructure

The aim of the study was to deliver alpha-tocopherol by a combination of prodrug and entrapment techniques, and to evaluate the ability of entrapped alpha-tocopherol to inhibit lipid oxidation in an oil-in-water emulsion. The amphiphilic alginate-alpha-tocopherol conjugate was synthesized via esterification reaction and confirmed by IR, H-1 NMR, and fluorescence spectroscopy as well as esterase hydrolysis. The bound alpha-tocopherol in the conjugate was 20.6 mu mol/g. The conjugate self-assembled into nanostructures in water, with a critical association concentration of 0.076 g/L. The percent entrapment and loading efficiency of alpha-tocopherol in the self-assembled nanostructures of the conjugate were, respectively, 4.92-16.82% and 78.83-92.32%, depending on the initial loading of alpha-tocopherol. Both blank and alpha-tocopherol-loaded nanostructures presented a negative zeta potential ranging from -50 to -65 mV and exhibited spherical shape with particle sizes in the range of 190-253 nm. More than 40% of alpha-tocopherol was retained after 216 h (i.e. 9 days) in phosphate buffer solutions (pH 7.4). The release of alpha-tocopherol was faster for nanostructures with lower alpha-tocopherol theoretical loading. Based on the thiobarbituric acid reactive substances assay for lipid oxidation, the blank nanostructures of the conjugate did not show antioxidant activity while the alpha-tocopherol-loaded nanostructures protected lipids against oxidation better than free alpha-tocopherol entrapped in the oil phase or in Tween 20 micelles. The results indicated that the newly prepared alpha-tocopherol-loaded nanostructure is a promising platform for solubilizing and delivering antioxidant activity of alpha-tocopherol in aqueous dispersions. (C) 2017 Elsevier Ltd. All rights reserved.