Coffee industrial residue: sequential high pressure extraction and conventional methods

Coffee industry generates large amounts of organic waste such as spent coffee grounds (SCG) and green coffee beans press cake (PC). The extraction of oil and phenolic compounds from PC was evaluated by: 1) Soxhlet extraction system using ethanol and hexane as solvent; 2) Extraction in a fixed bed at 400 bar and 60 °C using as solvent supercritical CO₂ (scCO₂), ethanol or a mixture scCO₂/ethanol 90:10 w/w; and 3) sequential extraction in a fixed bed at 400 bar and 60 °C using scCO₂ followed by pressurized liquid extraction with ethanol, followed by water. PC showed a residual oil content around 6%, which was extracted with pure scCO₂ and with hexane. Multi-stage extractions provide a statistically equal total extraction yield (p ≤ 0.05) to that obtained in a single step with ethanol, which was around 21%. However, ethanolic extract in one step presented about 96 mg CAE/g extract and the ethanolic and aqueous extracts obtained in the sequential stages showed 159 mg CAE/g and 146 mg CAE/g, respectively. The residue from the mechanical extraction of green coffee oil has an important oil content and the amount of phenolic compounds is greater than that from SCG.