Extraction of α-humulene-enriched oil from clove using ultrasound-assisted supercritical carbon dioxide extraction and studies of its fictitious solubility

•A combined process of SC–CO2 and ultrasound extraction (USC–CO2) is proposed.•Compared to HRE and SC–CO2 extraction, the USC–CO2 process was more efficient.•The solubility of α-humulene decreased with increasing temperature and pressure.•The measured solubility of α-humulene correlated well with a density-based model.•The thermodynamic properties of α-humulene in SC–CO2 were calculated using these models. Clove buds are used as a spice and food flavoring. In this study, clove oil and α-humulene was extracted from cloves using supercritical carbon dioxide extraction with and without ultrasound assistance (USC–CO2 and SC–CO2, respectively) at different temperatures (32–50°C) and pressures (9.0–25.0MPa). The results of these extractions were compared with those of heat reflux extraction and steam distillation methods conducted in parallel. The extracts obtained using these four techniques were analyzed using gas chromatography and gas chromatography/mass spectrometry (GC/MS). The results demonstrated that the USC–CO2 extraction procedure may extract clove oil and α-humulene from clove buds with better yields and shorter extraction times than conventional extraction techniques while utilizing less severe operating parameters. Furthermore, the experimental fictitious solubility data obtained using the dynamic method were well correlated with density-based models, including the Chrastil model, the Bartle model and the Kumar and Johnston model.