A new approach for increasing ascorbyl palmitate stability by addition of non-irritant co-antioxidant.

The aim of this work was to test innovative approach for enhancing ascorbyl palmitate stability in microemulsions for topical application by addition of newly synthesized co-antioxidant 4-(tridecyloxy)benzaldehyde oxime (TDBO) and to investigate its antioxidant activity and finally to evaluate cytotoxicity of TDBO-loaded microemulsions on keratinocyte cells. TDBO significantly increased ascorbyl palmitate stability in oil-dispersed-in-water (o/w) microemulsions, most presumably due to reduction of ascorbyl palmitate radical back to ascorbyl palmitate, since TDBO free-radical scavenging activity was confirmed. Cytotoxicity experiments demonstrated no significant change in cell viability or morphology in the presence of TDBO-loaded microemulsions regarding unloaded microemulsions, although greater cytotoxicity was observed with increased microemulsion concentrations. Therefore, the incorporation of TDBO as non-cytotoxic co-antioxidant in o/w microemulsions is a promising new strategy for enhancing ascorbyl palmitate stability that could be used to support antioxidant network in the skin.