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 (IC 50 ): Oxygen radical absorbance capacity (ORAC, IC 50 1.78 μg mL −1 )>Trolox equivalent antioxidant capacity (TEAC, IC 50 3.47 μg mL −1 )>2,2‐Diphenyl‐1‐picrylhydrazyl (DPPH, IC 50 5.83 μg mL −1 )> β ‐carotene bleaching (IC 50 11.58 μg mL −1 )>Ferric reducing antioxidant power (FRAP, IC 50 17.28 μg mL −1 ). Moreover, ACE was able to inhibit in vitro tyrosinase activity (IC 50 77.44 μg mL −1 ), l ‐DOPA auto‐oxidation (IC 50 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.