Optimization of process parameters in preparation of tocotrienol-rich red palm oil-based nanoemulsion stabilized by Tween80-Span 80 using response surface methodology

Abstract

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.

Fig 1. The effect of homogenization pressure and cycle on droplet size of nanoemulsion at 20 wt% of red palm oil (RPO), 5wt% of surfactant (Tween 80 only), 10 wt% of glycerol and 65wt% water (n = 3).

Fig 2. The effect of 5 wt% and 10 wt% of mixed surfactant (HLB 11& 14) on droplet size at 25°C storage temperature.

The nanoemulsions were prepared at 20 wt% oil, 10 wt% glycerol, 60–65 wt% water, while 5 wt% and 10 wt% total mixed surfactant, at the homogenization pressure and cycle of 600 bar and 4 cycles, respectively.

Fig 3

Normal probability plot residual for droplet size (A) & polydispersity index (B).

Fig 4. Effect of surfactant concentration, glycerol concentration in aqueous phase and homogenization pressure on droplet size of red palm oil (RPO) nanoemulsion.

Response surface plot showing the effect of (A) 10 wt% of surfactant concentration and 20 wt% of glycerol concentration, (B) 10 wt% of surfactant concentration and 600 bar homogenization pressure, (C) 20 wt% of glycerol concentration and 600 bar homogenization pressure, on droplet size of red palm oil (RPO) nanoemulsion, missing independent variable in each figure was kept at the centre point.

Fig 5. Effect of surfactant concentration, glycerol concentration in aqueous phase and homogenization pressure on polydispersity index of red palm oil (RPO) nanoemulsion.

Response surface plot showing the effect of (A) 10 wt% of surfactant concentration and 20 wt% of glycerol concentration, (B) 10 wt% of surfactant concentration and 600 bar homogenization pressure, (C) 20 wt% of glycerol concentration and 600 bar homogenization pressure, on polydispersity index (PDI) of red palm oil (RPO) nanoemulsion, missing independent variable in each figure was kept at the centre point.

Fig 6. TEM image of red palm oil-in-water nanoemulsions.

Scale bar represents 200nm.