Influence of the Solvent on the Extraction of Phenolic Com-pounds from the Coffee Grounds by Soxhlet Leaching

Abstract

In this study, phenolic compounds were extracted from the essential oil of coffee grounds originated in the coffee industry in the city of Guayaquil, Ecuador. The selected method was Soxhlet leaching, with three types of solvents (methanol, ethanol, and hexane), in its conventional form (solid-liquid), with two polar solvents and one nonpolar solvent, and in four extraction periods (30, 60, 90, and 120 minutes). The highest phenolic concentration and the best associative capacity were obtained with ethanol as the solvent for extraction, while the use of methanol yielded the second-best results. The extraction performance regarding the coffee grounds oil obtained higher results when using methanol, but close values were obtained with ethanol. Methanolic extracts obtained from coffee grounds can cause the formation of undesirable substances and be responsible for the methanolysis of gallic depsides. Therefore, the solvent-assisted technique depends on the selectivity and affinity of the compounds, according to their polar covalent character, the molecular geometry of the solvent, its relationship with its dielectric constant, and the null generation of unwanted reactions during extraction.