The depigmenting effect of kojic acid esters synthesized by the esterification of kojic acid using Rhizomucor miehei immobilized lipase was investigated in B16F1 melanoma cells. The depigmenting effect of kojic acid and kojic acid esters was evaluated by the inhibitory effect of melanin formation and tyrosinase activity on alpha-stimulating hormone- (α-MSH-) induced melanin synthesis in B16F1 melanoma cells. The cellular tyrosinase inhibitory effect of kojic acid monooleate, kojic acid monolaurate, and kojic acid monopalmitate was found similar to kojic acid at nontoxic doses ranging from 1.95 to 62.5 μg/mL. However, kojic acid monopalmitate gave slightly higher inhibition to melanin formation compared to other inhibitors at doses ranging from 15.63 to 62.5 μg/mL. Kojic acid and kojic acid esters also show antioxidant activity that will enhance the depigmenting effect. The cytotoxicity of kojic acid esters in B16F1 melanoma cells was significantly lower than kojic acid at high doses, ranging from 125 and 500 μg/mL. Since kojic acid esters have lower cytotoxic effect than kojic acid, it is suggested that kojic acid esters can be used as alternatives for a safe skin whitening agent and potential depigmenting agents to treat hyperpigmentation.
Red palm oil (RPO) is a natural source of Vitamin E (70-80% tocotrienol). It is a potent natural antioxidant that can be used in skin-care products. Its antioxidant property protects skin from inflammation and aging. In our work, a tocotrienol-rich RPO-based nanoemulsion formulation was optimized using response surface methodology (RSM) and formulated using high pressure homogenizer. Effect of the concentration of three independent variables [surfactant (5-15 wt%), co-solvent (10-30 wt%) and homogenization pressure (500-700 bar)] toward two response variables (droplet size, polydispersity index) was studied using central composite design (CCD) coupled to RSM. RSM analysis showed that the experimental data could be fitted into a second-order polynomial model and the coefficients of multiple determination (R2) is 0.9115. The optimized formulation of RPO-based nanoemulsion consisted of 6.09 wt% mixed surfactant [Tween 80/Span 80 (63:37, wt)], 20 wt% glycerol as a co-solvent via homogenization pressure (500 bar). The optimized tocotrienol-rich RPO-based nanoemulsion response values for droplet size and polydispersity index were 119.49nm and 0.286, respectively. The actual values of the formulated nanoemulsion were in good agreement with the predicted values obtained from RSM, thus the optimized compositions have the potential to be used as a nanoemulsion for cosmetic formulations.