Abstract:
Melanin protects human skin from ultraviolet radiation. However, abnormal
melanin production leads to pigmentation problems. Since tyrosinase is the
key enzyme that catalyzes melanin synthesis in humans, tyrosinase inhibitors
could be a desirable therapy option for hyperpigmentation. Though several
natural and synthetic regulators have been identified, the discovery of novel
selective and potent plant-based tyrosinase inhibitors that are less hazardous
to human health is still in development. Hence, this study investigated the
tyrosinase inhibitory activity of the leaf extracts of Dialium ovoideum
thwaites. Sequential extraction was conducted for leaves of D. ovoideum
thwaites using hexane, ethyl acetate and methanol at room temperature for 24
hours for each solvent.The extracts were evaluated for their total phenolic
content, antioxidant activity (DPPH radical scavenging assay) and tyrosinase
inhibitory activity (dopachrome method). The methanol extract possessed the
highest phenolic content of 80.59±1.88 mg GAE/g, antioxidant properties of
IC50 value of 300±1.04 μg/mL (compared to IC50 value of ascorbic acid of
36±0.69 μg/mL), and 12%-44% tyrosinase inhibitory activity at a
concentration range of 4.0-32.0 mg/mL (compared to kojic acid of 58%-61%).
These results suggest that the methanol extract of leaves of D. ovoideum
thwaites exhibits moderate tyrosinase inhibition which is positively correlated
with its antioxidant properties and total phenolic content.
