Enhanced extraction of spent coffee grounds oil using high-pressure CO2 plus ethanol solvents

Abstract

This work reports the extraction of spent coffee grounds (SCG) oil using supercritical CO2 plus ethanol (scCO2+EtOH) solvent in semi-batch process as an alternative approach to the use of organic solvent extraction. In addition, the results are compared to supercritical carbon dioxide (scCO2) and pressurized ethanol (EtOH). Soxhlet was performed and used as a standard extraction method. The extraction yield, fatty acid profile, total phenolic content (TPC), antioxidant activity (AA by ABTS and DPPH methods), phenolic compounds and caffeine content were determined, as well the overall extraction curves. The highest extraction yield of 15.9% was obtained using scCO2+EtOH using an ethanol to SCG ratio mass of (2:1), 80 ºC, 20 MPa in 25 min of extraction time. Major fatty acids present in the oil were linoleic (45%) and palmitic (31%). The oil obtained with scCO2+EtOH (2:1) presented high TPC values (294.47 to 392.96 mg GAE/100 g oil), similar to those obtained by pressurized ethanol extraction. High values of AA by ABTS and DPPH methods were also found in the oil from scCO2+EtOH extraction. The main phenolic acids found were dihydroxybenzoic acid and caffeic acid. The highest concentrations of dihydroxybenzoic (17.66 mg/100 g oil) and caffeic acid (9.36 mg/100 g oil) were obtained with scCO2+EtOH (2:1) at 80 ºC and 10 MPa. The highest caffeine content (711.70 mg/100 g oil) was obtained with scCO2+EtOH (0.5:1) at 60 ºC and 15 MPa. The results obtained in this work provided higher extraction yield when compared to scCO2 and similar to compressed ethanol, however in a shorter extraction time and using lesser organic solvent amounts. The results are promising and demonstrate the technical feasibility of SCG oil extraction using scCO2+EtOH to obtain valuable a product from an agricultural and urban waste biomass.