The research of new tyrosinase inhibitors is currently important for the development of skin whitening agents; particularly, birch leaves extracts are included in many skin cosmetic products. In this study, the potential ability of Betula pendula leaves ethanolic extract (BE) was evaluated on mushroom tyrosinase activity. Results showed that BE was capable to inhibit dose-dependently l-DOPA oxidation catalyzed by tyrosinase. The inhibition kinetics, analyzed by Lineweaver-Burk plots, showed a noncompetitive inhibition of BE towards the enzyme, using l-DOPA as substrate. The inhibitory mechanism of BE as studied by spectrophotometric analysis, demonstrated its ability to chelate copper ion in the active site of tyrosinase. In addition, BE exhibited Fe(2+)-chelating ability (IC(50)=614.12±2.14 μg/mL), reducing power and radical-scavenging properties (IC(50)=137.22±1.98 μg/mL). These results suggest the usefulness of birch leaves extracts in cosmetic and pharmaceutical industries for their skin-whitening and antioxidant effects. Determination of the polyphenolic compounds in BE extracts was afterward achieved by means of high-performance liquid chromatography (HPLC) with photodiode array (PDA) and mass spectrometry (MS) detection. A total of 25 compounds were positively identified, through the complementary analytical information, and are reported in such a matrix for the first time. Knowledge on the qualitative composition and contents of these natural sources in fact represents mandatory information, for rational consumption and correlation of the beneficial effects to the specific amounts.
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