Skin Permeation and Oxidative Protection Effect of Soybean Isoflavones from Topical Nanoemulsions—a Comparative Study of Extracts and Pure Compounds

Soybean isoflavone-rich extracts have been considered as promising skin antiaging products due to their antioxidant activity. This study investigates the effect of soybean isoflavone forms on porcine ear skin permeation/retention from topical nanoemulsions and their potential in protecting skin against oxidative damage caused by UVA/UVB light. Soybean non-hydrolyzed (SNHE) and hydrolyzed (SHE) extracts, mainly composed of genistin and genistein, were produced. Nanoemulsions containing SNHE (NE SNHE ) and SHE (NE SHE ) were prepared by spontaneous emulsification procedure and yielded monodispersed nanoemulsions. A delay of isoflavone release was observed after extracts incorporation into nanoemulsions when compared to a propyleneglycol dispersion of pure compounds. An increase of isoflavone skin retention from nanoemulsions was also achieved. However, from extracts, a higher amount of genistin (NE SNHE ) and a lower amount of genistein (NE SHE ) were detected in the skin in comparison to pure isoflavones. Finally, the protection of porcine ear skin by formulations against UVA/UVB oxidative stress was evaluated. Extract-loaded nanoemulsions offered better skin protection than pure isoflavones. Skin lipids were similarly protected by NE SHE and NE SNHE , whereas skin proteins were more protected by NE SNHE . Overall, nanoemulsions containing isoflavone-rich soybean extracts may be considered a better topical formulation aiming skin protection from UVA/UVB oxidative damage.