Conventional and pressurized ethanolic extraction of oil from spent coffee grounds: Kinetics study and evaluation of lipid and defatted solid fractions

Abstract

Extraction kinetics of spent coffee grounds (SCG) soluble in absolute (ET0) and hydrous ethanol (ET6) in the temperature range of 60–150 ℃, under atmospheric and pressurized conditions, are discussed in this work. Solvent hydration negatively impacted oil extraction, while an increase in temperature led to higher relative yields (≤ 96.8%) during SCG oil (SCGO) extraction. At 150 °C, ET0 and ET6 exhibited similar SCGO extraction efficiencies. Free fatty acids and chlorogenic acid were extracted in less amounts. Thus, a change in the physicochemical characteristics of ET6 was observed at high temperatures. The solvent became less polar. Low (≤ 3.49%) average relative deviation values were obtained via mathematical modeling considering washing and diffusion steps. This helped in the estimation of SCGO diffusion coefficients. The values of the diffusion coefficients increased with temperature. The values were comparable to the values obtained when hexane was used as the extraction solvent. These findings reveal the SCGO extraction efficiency of ethanol, mainly under conditions of high pressure.