Anti-Tyrosinase and DPPH Radical Scavenging Activities of Selected Thai Herbal Extracts Traditionally Used as Skin Toner

Introduction: Skin darkness may be cosmetically undesirable for some people. Plant-derived materials traditionally used for skin lightening may produce satisfactory results. Besides innate tyrosinase activity, oxidative stress also plays an important role in skin darkness by activating tyrosinase. Therefore, herbal extracts with strong anti-tyrosinase and antioxidant activities could be considered as efficacious skin lightening agents. The aims of the present study were to determine the anti-tyrosinase and antioxidant activities of Thai medicinal plant extracts indigenously used as skin toners. Methods: The activities of seven Thai medicinal plants; Zingiber cassumunar Roxb., Phyllanthus emblica Linn., Tagetes erecta Linn., Centella asiatica, Raphanus sativusvar. Longipinnatus Linn., Cassia fistula Linn. and Butea monosperma (Lam.) Taub. were investigated using the DOPA-chrome method to determine anti-tyrosinase activity and the DPPH free radical scavenging assay to determine antioxidant activity. Results: With respect to tyrosinase inhibitory activity, P. emblica, B. monosperma and R. sativusvar. Longipinnatus extracts at a concentration of 1.67 mg/mL showed strong activities with the percentage of tyrosinase inhibition at 48.38±4.77, 46.92±3.77 and 42.85±6.54%, respectively. In addition, P. emblica and B. monosperma extracts also exhibited high antioxidant activities with the IC50values on 33.47±1.24 and 33.57±1.92 mg/mL, respectively. Conclusion: Based on tyrosinase inhibition activity and DPPH radical scavenging assays, the herbal extracts of P. emblica and B. monosperma show promise as potential skin lighteners in cosmetic formulations.