Valorization of waste coffee silverskin as a source of antioxidant by extraction with agitation

Abstract Coffee is the second most traded commodity after petrol. The coffee industry produces about 23 million tonnes of waste every year. This implies that the unutilized portion of coffee carries a broad economic and environmental burden. The unutilized portion of coffee includes pulp, mucilage, parchment, husk, silver skin, and spent coffee grounds, each of which has its innate capacity to be reused for various industrial and domestic purposes. Coffee silverskin represents about 4.2% (w/w) of the coffee bean. Moreover, coffee silverskin contains phenolic compounds which have been studied extensively on account of their antioxidant properties. The main aim of the research is to convert coffee silver skin which is discarded as waste in coffee production, into a source of antioxidants that has wide application in the cosmetic and skincare industry. In this paper, conventional extraction methods for varying extraction temperatures (30–70°C), various solvents (n‐hexane, ethyl acetate, acetone, and ethanol) and extraction times (30, 60, and 90 min) were investigated to study their impact on the percentage of the coffee silverskin's antioxidant composition and the antioxidant property along with its total phenolic content (TPC) in coffee silverskin. It was found that ethanol was a suitable solvent and compared to the 50% ethanol‐water mixture, the 90% ethanol‐water mixture showed the highest extraction efficiency at the conditions of 70°C and 60 min for a TPC from coffee silverskin at 213 GAE mg/L.