Enhanced extraction of hydroxytyrosol, maslinic acid and oleanolic acid from olive pomace: Process parameters, kinetics and thermodynamics, and greenness assessment.

Three techniques of ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) and solvent extraction (SE) were used for enhancing the hydroxytyrosol (HT), maslinic acid (MA) and oleanolic acid (OA) extraction from olive pomace, being evaluated and compared through process parameters, kinetics and thermodynamics, plus greenness assessment analysis. Results showed that UAE yielded the maximum compounds due to a strong cavitation effect and the strongest mass and heat transfer efficiency involving the kinetic constants (h, Ce and K) and thermodynamic parameters (△H, △S and △G). Additionally, the optimal extraction conditions were acquired: ethanol concentration of 90%, extraction temperature of 50 °C, extraction time of 5 min, liquid to solid ratio of 30 mL/g, ultrasound intensity of 135.6 W/cm2, and ultrasound frequency of 60 kHz. UAE was confirmed as an effective and greener technique with the lowest E factor, energy consumption and carbon emission during the extraction process of bioactive compounds from olive pomace.