JOURNAL OF COSMETIC SCIENCE 320 extract powder had a total phenolic content of 188.83 mg GAE/g solid extract, which is slightly lower than that of the extract solution before drying of 210.27 mg GAE/g solid extract, as shown in Table II. The decrease in the total phenolic content after drying occurred because the extract was treated at a high temperature of 170°C during the spray drying process. The heating of the extract degraded some phenolic compounds, resulting in a lower phenolic content of the dried extract. A similar phenomenon was also reported by Orphanides et al. (19) who studied the effect of drying on the phenolic content and anti- oxidant capacity of spearmint. The effect of drying on the antioxidant activity can be seen in Table II. The antioxidant activity of the extract is expressed as IC50 value, which means the concentration of the sample needed to inhibit 50% of DPPH as the free radical. Thus, a low value of IC50 corresponds to a high antioxidant activity. As can be seen, the IC50 value of the extract powder was 433.64 ppm, higher than that of the extract solution of 358.15 ppm. This result is in accordance with the decrease in the total phenolic content after the drying process as described earlier. SKIN GEL CONTAINING COFFEE SIL VERSKIN EXTRACT The basic skin gel was prepare d using the formulation and the method described previ- ously. The coffee silverskin extract powder was then added to the basic skin gel and mixed Figure 3. Effect of extraction temperature on the total phenolic content of the coffee silverskin extract solu- tion (extraction time: 60 min).

DEVELOPMENT OF ANTIOXIDANT SKIN GEL USING COFFEE SILVERSKIN 321 together at room temperature to obtain a homogeneous gel. The concentration of the coffee silverskin extract powder in the skin gel varied at 0.125%, 0.25%, 0.5%, and 1%. Figure 6 shows the physical appearance of the skin gels with different extract concentrations. Figure 4. Effect of extraction temperature on the antioxidant activity of the coffee silverskin extract solution (extraction time: 60 min). Figure 5. Coffee silverskin extract solution and powder form.