J. Cosmet. Sci., 70, 313–325 (November/December 2019) 313 Utilization of Coffee Silverskin By-Product from Coffee Roasting Industry through Extraction Process for the Development of Antioxidant Skin Gel SAMUEL P. KUSUMOCAHYO, PATRICK TANGGUH, CHRISTINA D. ANNELIES, and HERY SUTANTO , Department of Chemical Engineering, Faculty of Life Sciences & Technology, Swiss German University, Tangerang 15143, Indonesia (S.P.K., P.T., C.D.A., H.S.) Accepted for publication October 4, 2019. Synopsis Coffee roasting industries generate a by-product called coffee silverskin that is usually disposed of as waste. The valorization of this abundant waste is necessary because of the antioxidant compounds in coffee silverskin. In this study, coffee silverskin was extracted in different extraction conditions to obtain an extract with high antioxidant activity and to use it as an additive for antioxidant skin gel. The extracts were characterized for the total phenolic content by using the Folin–Ciocalteu method. The antioxidant activity was determined by using the 2,2-diphenyl-1-picrylhydrazyl free radical scavenging assay. It was found that the extraction time and temperature strongly affected the total phenolic content and the antioxidant activity of the extracts. The extraction at 40°C and 60 min resulted in an extract with a high total phenolic content of 31.15 ± 2.77 mg Gallic Acid Equivalent/g coffee silverskin and a high antioxidant activity of 68.44 ± 0.76%. The extract solution was spray-dried to produce extract powder, which was then added to a basic skin gel with different extract concentrations. It was observed that the antioxidant activity of the gel increased with increasing extract concentration in the gel. This result showed that coffee silverskin has great potential as a source of antioxidants for various skin care products. IN TRODUCTION Anti oxidants are very important for the human body because they protect the human body against reactive oxygen species, known as free radicals, which can cause oxidative reac- tions in human cells. Although the human body has an internal defense system toward free radicals (1), it still requires the intake of antioxidants from outside that usually can be obtained from synthetic or natural products, such as fruits and vegetables, containing antioxidants (2). Recently, the interest in natural products for healthy foods, beverages, supplements, and health care products has been rising along with the increasing aware- ness of a healthy life style (3–5). Address all correspondence to Samuel P. Kusumocahyo at samuel.kusumocahyo@sgu.ac.id.

JOURNAL OF COSMETIC SCIENCE 314 One of the most popular and valuable natural products is coffee. Because of the high consumption of coffee as a beverage, the coffee industry is categorized as one of the largest industries in the world (6). Besides its good taste, coffee is benefi cial for human health because many studies have shown that coffee contains phenolic compounds such as chlorogenic acids, which show antioxidant activity (7,8). The coffee industries also produce a large number of by-products, such as coffee spent grounds and coffee silver- skin (9). Coffee silverskin is produced as a by-product during the roasting process of coffee beans. It is a thin layer surrounding the coffee bean, and it is usually still at- tached to the coffee bean even after the depulping and dehulling process of the coffee cherries. When the coffee beans are heated at high temperature during the roasting process, the coffee beans will crack because of loss of moisture content, resulting in the detachment of the coffee silverskin from the beans. Because of its lightness, the coffee silverskin escapes from the roasting container through the roaster exhaust or cyclone, and is usually disposed of as waste. However, recent studies on the revalorization of coffee silverskin reported that coffee silverskin contains phenolic compounds and shows high antioxidant activity (10–12). Bresciani et al. (13) reported that chlorogenic acids are the sole phenolic compounds in coffee silverskin. The studies on the extrac- tion of coffee silverskin mostly used a mixture of Robusta and Arabica coffee silverskin because the roasting industry usually blends these two types of coffee. However, our recent study showed that Robusta coffee silverskin showed a higher phenolic content and, thus, a higher antioxidant activity than Arabica coffee silverskin (14). This re- sult is in accordance with the study conducted by Farah et al. (8) who reported that Robusta coffee beans contain a higher amount of chlorogenic acid than Arabica coffee beans. Rodrigues et al. (15) reported that coffee silverskin was an effective ingredient in the improvement of skin hydration and fi rmness. De Hond et al. (16) studied the use of coffee silverskin extract to protect accelerated skin aging. In spite of the high antioxidant activ- ity of coffee silverskin and its great potential for industrial application, to the best of our knowledge, there is no study on the development of skin care products containing coffee silverskin extract as an antioxidant. Moreover, a proper extraction method and the opti- mization of the extraction condition to obtain an extract of coffee silverskin with a high phenolic content and a high antioxidant activity are not studied yet. Furthermore, the extraction of coffee silverskin was usually conducted by maceration process, which means the raw material is immersed in a solvent without any mechanical agitation. This conven- tional method takes a long time to extract the phenolic compounds, and results in a low phenolic content. In t his work, coffee silverskin of Robusta type was extracted using a hydroalcoholic solvent with the aid of mechanical agitation at various extraction times and tempera- tures with the purpose to maximize the phenolic content and the antioxidant activity of the coffee silverskin extract. The extract solution was then dried using a spray dryer to produce coffee silverskin extract in powder form. The study on the effect of drying of the extract is important because extracts are usually produced in powder form. Furthermore, to develop an antioxidant skin care product, a basic skin gel was prepared and the coffee silverskin extract powder was added as an active ingredient in the skin gel. The total phenolic content and the antioxidant activity of the skin gel were measured to study the effect of the addition of the coffee silverskin extract to the skin gel.