Identifying an isoflavone from the root of Pueraria lobata as a potent tyrosinase inhibitor

Traditionally, the root of Pueraria lobata are widely used as a functional food. It was observed that a 70% ethanol extract showed a dose-dependent inhibition towards mushroom tyrosinase. Among the different isolated compounds, calycosin demonstrated potent inhibitory activity against substrates L-tyrosine and L-DOPA, with IC50 of 1.45 +/- 0.03 and 7.02 +/- 0.46 mu M, respectively. Conversely, formononetin and daidzein exhibit weak inhibition. Moreover, kinetic studies revealed calycosin to be a competitive inhibitor for both substrates. Additionally, molecular docking simulation showed that the hydroxyl groups at C-3' and C-7 positions interacted with the catalytic site and peripheral residues, demonstrating a higher affinity toward mushroom tyrosinase. Accordingly, our results suggest that, rather than a mono-substituted hydroxyl or methoxyl group, the presence of a hydroxyl group at C-3' and a methoxyl group at C-4' position of the isoflavone skeleton plays an essential role in the manifestation of anti-browning activity in food products.