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).

DEVELOPMENT OF ANTIOXIDANT SKIN GEL USING COFFEE SILVERSKIN 319 in the extraction temperature above 40°C did not result in a signifi cant increase in the antioxidant activity of the extract (p 0.05). This result indicated that all phenolic com- pounds were completely extracted from the coffee silverskin at an extraction temperature of 40°C and an extraction time of 60 min. This is very interesting because an extraction temperature of 40°C is appropriate for the industrial scale extraction process because of the lower energy consumption for heating. COFFEE SILVERSKIN EXTRACT POWDER Based on the aforementione d results, coffee silverskin extract in powder form was prepared by drying the coffee silverskin extract solution using a spray dryer. First, the extract solution was prepared by extracting the coffee silverskin at 40°C for 60 min because this extrac- tion condition resulted in a high total phenolic content and a high antioxidant activity. Then, the fi ltered extract solution was dried using a spray dryer at an inlet temperature of 170°C and an outlet temperature of 125°C. Figure 5 shows the picture of the extract solution before drying and the extract powder after drying. The measurement of the moistu re content showed that the dried coffee silverskin extract powder had a moisture content of 5.6%. The analysis of the total phenolic content using the Folin–Ciocalteu method with GA as a standard showed that the coffee silverskin Figure 2. Effect of extraction time on the antioxidant activity of the coffee silverskin extract solution (ex- traction temperature: 40°C).