Solid lipid nanosuspensions based on low melting lipids as protective system of retinyl palmitate

Solid lipid nanoparticles (SLN) containing or not all-trans-retinyl palmitate (ATRP) were prepared by the hot homogenization technique, employing Witepsol (m.p. = 36.7 °C) and Precirol ATO (m.p. = 55.2 °C) as lipid phases. The nanosuspensions were characterized through particle size analyses and zeta potential measurements. In both systems the encapsulation efficiency was excellent. DSC experiments carried out on freeze-dried samples of SLN loaded with the vitamin showed the absence of the melting peak of retinyl palmitate. Samples of loaded SLN were maintained in the dark or under the direct action of light: the residue all-trans-retinyl palmitate in the time was determined by HPLC analysis. SLN prepared with Witepsol were able to preserve ATRP from the action of the light at least partially. Degradation studies were also performed on SLN loaded with different amount of vitamin and after the addition of a sunscreen.