Ultrasound-assisted deep eutectic solvent extraction of tyrosinase inhibitors from lotus seed peel powder

Lotus seed peel powder (LSP), a major by-product of lotus seed processing, is rich in bioactive constituents but remains largely underutilized. Conventional aqueous and ethanolic extraction methods for LSP are constrained by low extraction efficiency and poor selectivity. In this study, an ultrasound-assisted deep eutectic solvent (DES) extraction (UADE) strategy was developed to recover tyrosinase inhibitors from LSP. UADE significantly enhanced flavonoid and polyphenol extraction compared with traditional methods. Among the tested DESs, the L-proline/lactic acid system exhibited the highest selectivity for tyrosinase inhibitors. Using response surface methodology, the optimal extraction conditions were determined as follows: Pro to LA 1:2, 20 % water, solid-to-liquid ratio 1:40 (w/v), 47 °C, 300 W, 70 min. Under these conditions, the tyrosinase inhibition rate reached 96.51 %, and the half-maximal inhibitory concentration (IC₅₀) of the purified extract was 1.02 mg/mL. In addition, the DES system retained good reusability over multiple extraction cycles. Mechanistic analyses revealed that ultrasonic treatment markedly disrupted LSP cell wall structure, promoting the release of active components. Four key tyrosinase inhibitors, including isorhamnetin-3-O-galactoside-6''-rhamnoside, were identified via UHPLC-QE-Orbitrap-MS analysis combined with molecular docking and molecular dynamics simulations. DFT calculations suggested that hydrogen bonding and π-π stacking interactions between DES components and key inhibitors were the core driving forces of extraction selectivity. Zebrafish assays confirmed that the extract inhibited tyrosinase activity in vivo and downregulated the expression of multiple melanogenesis-related genes. These findings establish UADE as an effective and selective approach for the extraction of tyrosinase inhibitors from natural resources, providing a methodological basis for developing anti-melanogenic cosmetic ingredients.