Taguchi-Based Optimization of Ultrasound-Assisted Valorization of Coffee Silver Skin for Increasing Phenolic Content: Antioxidant Activity, Physical Properties, and Energy Consumption Assessment

Coffee is among the trendy beverages; however, roasting coffee beans generates by-products such as coffee silver skin (CS). Although CS is rich in phenolic compounds with potential health benefits, there are limited reports on applying advanced optimization approaches combined with emerging food processing technologies for sustainable valorization of CS. This study aims to optimize the ultrasound extraction process of Taiwanese CS using the L9 (34) orthogonal Taguchi method, aiming at maximizing total phenolic content (TPC) while assessing total and specific energy consumption (TEC and SEC). The antioxidant activity of the extracts was also evaluated in relation to processing variables. Besides, variations in the extracts’ CIE color values and total soluble solids were assessed. Independent parameters were extraction time, sonication amplitude, ethanol concentration, and temperature. According to the results, optimized conditions (1 min, 50% amplitude, 80% ethanol, and 25 °C) yielded a TPC value of 7.45 mg GAE/g CS, with the lowest SEC of 0.0067 kWh/mg GAE/g. Antioxidant analysis showed a range of 0.634–1.283 mg/mL for 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability, indicating Taguchi’s effectiveness in improving antioxidant activity. In addition, process optimization reduced TEC and SEC by 23.8 and 41.8%, respectively, contributing to green extraction and sustainable food production in line with sustainable development goals. It was found that selecting optimal parameters is crucial for maximizing the extraction of phenolic and enhancing antioxidant properties, while minimizing energy use. Future chemistry-focused studies can explore the interactions between individual phenolic compounds in CS extracts to further support the optimization of multi-parameter process design.