Encapsulation of ascorbyl palmitate in nanostructured lipid carriers (NLC)--effects of formulation parameters on physicochemical stability.

Enhancement of the chemical stability of ascorbyl palmitate (AP) after incorporation into nanostructured lipid carriers (NLC) has been reported. However, the formulation parameters of AP-loaded NLC have not been completely investigated. Moreover, the long-term chemical stability of AP in any colloidal systems has not been yet achieved. Therefore, in this study the formulation parameters affecting the stability of AP after incorporation into NLC were evaluated including types of lipids, types of surfactants, storage conditions, i.e. temperature and nitrogen gas flushing, the effects of drug loading as well as types of antioxidants. After storage for 90 days, the mean particle size analyzed by photon correlation spectroscopy (PCS) was lower than 350 nm. The zeta potential measured by the Zetasizer IV was higher than -30 mV in all developed AP-loaded NLC formulations which varied according to the types of lipid and surfactant. Concerning the chemical stability of AP, it was found that AP-loaded NLC prepared and stored in non-degassing conditions, a higher percentage of AP loading in NLC, lower storage temperature (4 degrees C), addition of antioxidants as well as selection of suitable surfactants and solid lipids improved the chemical stability of AP. Moreover, an improvement of long-term chemical stability of AP was achieved by addition of antioxidants with nitrogen gas flushing as compared to those without antioxidant. The percentage of drug remaining at both 4 degrees C and room temperature (25 degrees C) was higher than 85% during 90 days of storage.