Polyphenol Characterization, Antioxidant and Skin Whitening Properties of Alnus cordata Stem Bark

In this study, we investigated the phenolic composition of the crude extract (MeOH 80 %) of Alnus cordata (Loisel.) Duby stem bark (ACE) and its antioxidant and skin whitening properties. RP-LC-DAD analysis showed a high content of hydroxycinnamic acids (47.64 %), flavanones (26.74 %) and diarylheptanoids (17.69 %). Furthermore, ACE exhibited a dose-dependent antioxidant and free-radical scavenging activity, expressed as half-maximal inhibitory concentration (IC₅₀ ): Oxygen radical absorbance capacity (ORAC, IC₅₀ 1.78 μg mL^-1 )>Trolox equivalent antioxidant capacity (TEAC, IC₅₀ 3.47 μg mL^-1 )>2,2-Diphenyl-1-picrylhydrazyl (DPPH, IC₅₀ 5.83 μg mL^-1 )>β-carotene bleaching (IC₅₀ 11.58 μg mL^-1 )>Ferric reducing antioxidant power (FRAP, IC₅₀ 17.28 μg mL^-1 ). Moreover, ACE was able to inhibit in vitro tyrosinase activity (IC₅₀ 77.44 μg mL^-1 ), l-DOPA auto-oxidation (IC₅₀ 39.58 μg mL^-1 ) and in an in vivo model it exhibited bleaching effects on the pigmentation of zebrafish embryos (72 h post fertilization) without affecting their development and survival. In conclusion, results show that A. cordata stem bark may be considered a potential source of agents for the treatment of skin disorders due to its bleaching properties and favorable safety profiles, associated to a good antioxidant power.