Investigating the influence of solvents and extraction methods on the efficacy of phenolic compound recovery from spent coffee grounds

Spent coffee grounds (SCGs) represent a significant by-product with a high potential of extract bioactive compounds. This study investigates the potential of SCGs as a source for the extraction of phenolic compounds, which have applications in the pharmaceutical, cosmetic and food industries. In this work, several solvents and two extraction techniques were studied: Soxhlet as a reference and dynamic maceration for understanding the yield of extraction and the possible compounds that can be obtained. For dynamic maceration with a single liquid phase, higher extraction yields were observed for solvents with medium to high polarity, notably acetone (19.64 % ± 0.05) and isopropanol (14.66 % ± 0.76). Whereas ethanol (23.85 % ± 0.47) and acetone (20.03 % ± 0.27) led to best yields for Soxhlet. The primary phenolic compounds extracted were gallic acid, caffeic acid, 2,4-dihydroxybenzoic acid, 5-HMF, and furfural. In addition, when dynamic maceration and Soxhlet were tested with two liquid phases (a polar and a non-polar solvent), the yields were even better: 16.28 ± 2.01 % and 28.45 ± 2.48 %, respectively. A sustainability assessment was also made. Analytical Greenness Calculator indicated dynamic maceration (score: 0.6) as greener than the reference Soxhlet extraction (score: 0.5), requiring less energy, solvent, and time. These findings underscore the critical role of solvent selection in optimizing extraction processes, as well as the importance of selecting appropriate extraction techniques to maximize yield of value compounds in by-product like SCGs.