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.

JOURNAL OF COSMETIC SCIENCE 322 The color of the skin gel became darker when more extract powder was added to the gel. The gel viscosity ranges between 98,300 and 109,500 cps, with pH ranges between 6.5 and 7.0. Figure 7 shows the total p henolic content of the skin gels with various extract concen- trations. As can be seen, the total phenolic content in the skin gel increased by adding more coffee silverskin extract to the skin gel. The addition of the extract of more than 1% is still possible to obtain a skin gel with higher total phenolic content, but because the color of the skin gel will become darker, the color acceptance by the users should be considered. To study the effect of the add ition of the coffee silverskin extract on the antioxidant activ- ity of the skin gel, an analysis using DPPH free radical scavenging assay was conducted. It was observed that the basic skin gel that contains no coffee silverskin extract exhibited a DPPH inhibition percentage of only 3% because of the oxidation of the bulk skin gel by the DPPH. Interestingly, the skin gel containing 0.125% coffee silverskin extract exhibited a DPPH inhibition percentage of 26.3%, indicating that the coffee silverskin extract was effective as a source of antioxidants in the skin gel. Further, Figure 8 shows the effect of the addition of the coffee silverskin extract on the antioxidant activity Figure 6. Physical appearance of skin gels containing coffee silverskin extract at different concentrations (left to right: F1: 0.125%, F2: 0.25%, F3: 0.5%, F4: 1%). Table II Total Phenolic Content and Antioxidant Activity of Coffee Silverskin Extract before and after Drying Coffee silverskin extract solution (before drying) Coffee silverskin extract powder (after drying) Total phenolic content (mg GAE/g solid extract) 210.87 188.83 IC50 (ppm) 358.15 433.64