JOURNAL OF COSMETIC SCIENCE 74 comparison to the standard positive antioxidants (BHT, BHA, and α-tocopherol) using the DPPH, TBAR (Table I) and FRAP assays (Table II), which represent different mech- anisms of antioxidant activities. The ability of sesamol to inhibit radical scavenging and lipid peroxidation are presented with the IC50 value. The results showed that sesamol exerted the strongest radical scavenging activity over against the positive controls with an IC50 value 2 μg/ml (14.48 μM). Sesamol was able to inhibit lipid peroxidation more than BHT but not higher than BHA and α-tocopherol. Total antioxidant activity based on reducing power was measured by FRAP. The standard curve created by FeSO4 was plotted and was linear between 15.625 and 250 μM FeSO4 Table I. Effect of Sesamol, BHT, BHA and α-Tocopherol on Radical Scavenging Activity Using the DPPH Assay and Lipid-Peroxidation Using the TBAR Assay Compounds IC50 (μM) DPPH assay TBAR assay Sesamol 14.48a 6.15 ± 0.2b BHT 21.78 ± 0.9b 9.53 ± 1.4c BHA 40.50 ± 2.8c 1.55 ± 0.2a α-Tocopherol 19.73 ± 4.6b 3.02 ± 0.7a Results presented: mean ± S.D. (n = 3). Values with different superscripts in each column are significantly different (one-way ANOVA, p 0.05). Table II. Effect of Sesamol, α-Tocopherol, BHA, and BHT on Reducing Power as Determined by the FRAP Method Compounds Concentration (mM) FRAP value (μM FeSO4) Sesamol 0.0145 44.17 ± 2.22a 0.0282 84.23 ± 4.59b 0.0565 117.71 ± 14.51c 0.1129 189.88 ± 17.56d α-Tocopherol 0.0046 44.66 ± 4.12a 0.0091 75.91 ± 4.35b 0.0181 109.12 ± 9.07c 0.0362 165.75 ± 10.70d BHA 0.0111 10.75 ± 5.57a 0.0216 29.55 ± 6.86a,b 0.0433 45.59 ± 15.30b 0.0866 70.91 ± 14.04c BHT 0.0091 4.32 ± 2.94a 0.0177 10.21 ± 5.47a 0.0354 20.75 ± 3.62b 0.0708 33.79 ± 5.63c a–d Mean within a column of each compounds having the same superscripts are not signifi cantly different (p 0.05).

WHITENING AND ANTIAGING EFFECT OF SESAMOL 75 with R2 = 0.9603. After considering the activity of each compound, sesamol exhibited a total antioxidant power (84.23 ± 4.59 μM FeSO4) greater than BHT (20.75 ± 3.62 μM FeSO4) and BHA (45.59 ± 15.30 μM FeSO4), but lower than α-tocopherol (165.75 ± 10.70 μM FeSO4), respectively (Table II). Taken together, our results on radical scaveng- ing, lipid peroxidation activities, and reducing power indicate that sesamol possessed antioxidant activity with multiple mechanisms. INHIBITORY EFFECT OF SESAMOL ON MUSHROOM TYROSINASE IN VITRO The antimelanogenic activity of sesamol was principally evaluated on its inhibition of mushroom tyrosinase activity in vitro. The results showed that sesamol and kojic acid inhibited tyrosinase activity in a dose-dependent manner. The respective IC50 values for sesamol and kojic acid were 0.33 μg/ml (1.6 μM) and 6.15 μg/ml (67.6 μM) (Figures 1A and 1B.). The other positive control (β-arbutin) did not show any tyrosinase inhibitory activity (data not shown), despite using a concentration as high as 1000 μg/ml (3673 μM), indicating that sesamol blocked the tyrosinase enzyme with the strongest activity than the known whitening compounds, kojic acid and β-arbutin. EFFECT OF SESAMOL ON CELLULAR TYROSINASE INHIBITION To confi rm the ability of sesamol on inhibition of tyrosinase enzyme in the cells, the cel- lular tyrosinase inhibitory activity was evaluated in the SK-MEL2 cell model. The con- centration used in the cell-based assay was higher than that used in the inhibitory study of mushroom tyrosinase in vitro to ensure suffi cient accumulation of the test compound in the cells. The result showed that 30 μg/ml (217 μM) sesamol inhibited cellular tyrosinase activity 23.55 ± 8.25%, whereas 600 μg/ml (4222 μM) kojic acid o nly inhibited tyrosi- nase 33.88 ± 1.43% (Figure 2). Although kojic acid was used at higher concentration (4222 μM) than sesamol (217 μM), kojic acid showed a tyrosinase inhibitory activity (33.88 ± 1.43%) not signifi cantly different than sesamol (23.55 ± 8.25%) (p = 0.243). By comparison, although β-arbutin was used as high as 3673 μM, it could only inhibit cel- lular tyrosinase enzyme at 8.26 ± 8.78% (Figure 2). These results indicate that sesamol has potential as a whitening agent and possesses better activity than the currently used whitening compounds, kojic acid and β-arbutin. Figure 1. Effect of (A) sesamol and (B) kojic acid on mushroom tyrosinase inhibition. Data are presented as mean ± S.D. (n = 3).