Sustainable Valorization of Coffee Silverskin Waste: Pressurized Liquid Extraction of Bioactive Compounds

Coffee silverskin, a by-product of the coffee roasting industry, offers significant potential for valorization due to its bioactive compound content. This study optimized the Pressurized Liquid Extraction (PLE) process for recovering phenolic compounds and caffeine from coffee silverskin. A factorial design identified the temperature and ethanol concentration as the key parameters influencing extraction yield, antioxidant capacity (TEAC), total phenolic content (TPC) and caffeine and phenolic acid contents. These factors were further optimized using a central composite design (CCD) and Response Surface Methodology (RSM). The optimal extraction conditions-140 °C and 55% ethanol-achieved a balanced enhancement across all responses: 12.1% extraction yield, 65.3 mg TE/g dry extract for antioxidant capacity, 88.4 mg GAE/g dry extract for total phenolic content, 56.7 mg caffeine/g dry extract, and 10.6 mg chlorogenic acid equivalents/g dry extract for phenolic acid content. Compared to conventional methods, the optimized PLE demonstrated superior bioactive compound recovery while employing environmentally friendly solvents. This approach underscores PLE's potential as a sustainable technology for valorizing agro-industrial by-products, contributing to both waste reduction and the development of antioxidant-rich products.