DEVELOPMENT OF ANTIOXIDANT SKIN GEL USING COFFEE SILVERSKIN 317 DRYING OF COFFEE SILVERSKIN EXTRACT To produce coffee silverskin extract in powder form, the coffee silverskin extract solution was dried using a spray dryer with an inlet temperature of 175°C and an outlet tempera- ture of 125°C with a feed fl ow of 16.7 mL/min. The coffee silverskin extract powder was then analyzed for its total phenolic content and antioxidant activity using the method as previously described. PREPARATION OF COFF EE SILVERSKIN SKIN GEL A basic gel was pre pared by using the cold mechanical method as described by Schmolka (17) with some modifi cations. The composition of the ingredients for the basic skin gel is shown in Table I (18). First, Carbomer 940 was d issolved in distilled water in a glass beaker and stirred using a mixer to obtain a gel. The mixing process was carried out at room temperature at 600 rpm for 20 min. To reduce the bubble, the gel was kept for 24 h at room temperature. TEA was then added to the gel and mixed. Methylparaben and propylparaben were dissolved in propylene glycol, whereas EDTA was dissolved in distilled water by stirring. Then, these solutions were added into the gel and stirred until a homogeneous mixture was attained. Finally, the coffee silverskin extract powder which was already dissolved in distilled water, was added into the gel, and stirred at room temperature for 20 min. The concentration of the coffee silverskin extract powder in the skin gel varied at 0.125%, 0.25%, 0.5%, and 1%. The total phenolic content of the skin gel was analyzed using the method described previously. The antioxidant activity of the skin gel was also analyzed and expressed as IC50 value using the method described previously. The pH of the gel was measured using a pH meter, whereas the viscosity was measured using a viscometer using spindle number 6 at a speed of 3 rpm. All measurements were carried out at room temperature. RESULTS AND DISCUSS ION TOTAL PHENOLIC CONT ENT AND ANTIOXIDANT ACTIVITY OF COFFEE SILVERSKIN EXTRACT SOLUTION The coffee silversk in sample was extracted using water–ethanol (50:50 w/w) as solvent at different extraction times and temperatures. Water–ethanol mixture with a weight ratio Table I Composition for the Basic Skin Gel Ingredient Composition (g/100 g water) Carbomer 940 1 TEA 1 Propylene glycol 15 Methylparaben 0.15 Propylparaben 0.05 EDTA 0.05 Ethanol (96% v/v) 5 Perfume 0.4 Distilled water 100

JOURNAL OF COSMETIC SCIENCE 318 of 50:50 was chosen as the solvent because of the intermediate polarity of the phenolic compounds Ballesteros et al. (12). The extract solutions were then analyzed for their total phenolic content and antioxidant activity. Figures 1 and 2 show the effect of extraction time on the total phenolic content and the antioxidant activity of the coffee silverskin extract solution. The extraction was carried out at a constant extraction temperature of 40°C. As shown in Figure 1, a longer extraction time resulted in a higher amount of total phenolic content of the coffee silverskin extract solution. Because phenolic compounds are known to have antioxidant property, the antioxidant activity increased with increasing extraction time, as shown in Figure 2. The extraction time of 60 min showed the highest total phenolic content and antioxidant activity compared with the other extraction times. To study the effect of extraction temperature, the extraction experiment was carried out at different extraction temperatures at a constant extraction time of 60 min. Figures 3 and 4 show the effect of extraction temperature on the total phenolic content and the antioxidant activity of the coffee silverskin extract solution. When the extraction tem- perature was elevated from 30°C to 40°C, an increase in the total phenolic content was observed. However, a further increase in temperature above 40°C did not result in a sig- nifi cant increase in the total phenolic content as shown in Figure 3 (p 0.05). A similar phenomenon was also observed for the antioxidant activity as shown in Figure 4. An increase Figure 1. Effect of extraction time on the total phenolic content of the coffee silverskin extract solution (extraction temperature: 40°C).