The growing demand for safe and effective natural ingredients in cosmetic formulations has prompted research into marine-derived compounds, particularly phlorotannins from brown algae. These compounds exhibit diverse bioactivities, including tyrosinase inhibition, which is relevant for the treatment of skin hyperpigmentation disorders. This study aimed to optimize the ultrasound-assisted extraction (UAE) of phlorotannins from the brown macroalga Dictyopteris justii and to evaluate the in vitro tyrosinase inhibitory activity of the resulting extract. A Box–Behnken design was employed to optimize the extraction parameters: ethanol concentration, solid-to-liquid ratio, temperature, and time. Total phlorotannin content (TPhC) was quantified using the DMBA colorimetric method, and the optimized extract was evaluated for tyrosinase inhibitory activity using a commercial colorimetric assay. The IC₅₀ of the extract was determined and compared with kojic acid. The optimal extraction conditions were identified as 70% ethanol, a 1:10 solid-to-liquid ratio, 25 °C, and 20 min. Under these conditions, the TPhC reached 2.874 ± 0.069 mg phloroglucinol equivalents per gram of dry extract, with a 9% extraction yield. Chromatographic analysis suggests the presence of hydroxypentafuhalol-B in the extract.The optimized extract showed significant tyrosinase inhibitory activity with an IC₅₀ of 0.51 mg/mL, compared to 46.61 µg/mL for kojic acid. This study demonstrates the successful optimization of UAE for obtaining a phlorotannin-rich extract from D. justii with reproducible extraction efficiency and potent tyrosinase inhibition. These findings support the potential application of D. justii extracts in the development of cosmetic products targeting hyperpigmentation.
Rodríguez et al. (2026) studied this question.