Factors Affecting the Efficiency of Pressurized Solvent Extraction of Oil From Spent Coffee Grounds

Abstract

Spent coffee grounds (SCG) are the main residues of the coffee beverage industry, and a potentially valuable source of energy-dense lipids. The present study investigates the effect of temperature, pressure and duration on the pressurized solvent extraction of lipids from dried SCG to evaluate their impact on oil extraction efficiency, composition and energy content. Solvent extraction trials at elevated temperatures performed by an Accelerated solvent extraction (ASE) unit revealed a beneficial effect of increased temperature on the crude lipid extracting efficiency of polar ethanol. Nuclear magnetic resonance (NMR) analysis showed that extraction temperature had a significant impact on the proportions of the ASE-extracted SCG oil constituents, with increasing temperature leading to lower concentration of triglycerides and higher levels of 1,2-and 1,3-diglycerides. Experiments performed in a closed pressurized vessel allowed individual selection of pressure and temperature and showed that pressure had a significant impact on oil extracting efficiency that largely depended on process temperature. There was no systematic effect of extraction temperature and pressure on the higher heating value (HHV) of SCG lipid samples, which ranged between 38.53 MJ/kg and 39.12 MJ/kg, while extraction pressure was found to have negligible effect on the free fatty acid (FFA) content of lipids extracted by pressure vessel experiments. Prolongation of pressurized extraction duration above 10 minutes was found to be counterproductive in terms of oil recovery, and consecutive short extraction static cycles with fresh solvent removed higher amounts of SCG oil relative to a single longer cycle.

Valorization of spent coffee grounds by 2-methyloxolane as bio-based solvent extraction. Viable pathway towards bioeconomy for lipids and biomaterials

“…Previously reported data in the literature indicates that triglycerides and fatty acids are the predominant lipid class found in SCG oils. For instance, Efthymiopoulos et al (2019a) reported TAG concentrations ranging between 39% and 74% whereas fatty acids ranged from 11% to 33%. Meanwhile, diglycerides and monoglycerides were also found in SCG oils but the latter was found in higher amounts (8-23%) than the monoglycerides (0-6%).…”

Quality Attributes and Sensory Acceptance of Different Botanical Coffee Co-Products

“…Differences in silverskin lipid content can be partially attributed to factors such as different varieties of coffee, the origin of coffee beans, coffee-growing conditions (climate, time of harvest), and processing methods (wet or dry processing and roasting) [40,50,51]. Gottstein et al, Mota et al, and Efthymiopoulos et al [40,50,51] reported the fat content in silverskin (Coffee canephora) reaching 18.2 ± 0.1 g.kg −1 . Costa et al [12] reported that silverskin contains 24.2 g.kg −1 of fat.…”

Spent Coffee Grounds’ Valorization towards the Recovery of Caffeine and Chlorogenic Acid: A Response Surface Methodology Approach

“…As evidenced by Al-Hamamre et al [48], the higher yield was also affected by the increased duration of the extraction, which in the case of Soxhlet can take up to 24 h. However, according to the results (Figure 1), the method that prevailed over the other two was ASE, since the yields of all three solvents were higher than those obtained with either Soxhlet extraction or UAE. These results can be assigned to the fact that extraction was performed under higher than atmospheric pressure and a temperature close or above solvent's boiling point [39]. Thus, even though the temperature was high, the pressure kept the solvent in a liquid state and facilitated the extraction of compounds located within the matrix pores [40].…”

“…Depending on the combination of temperature and pressure, water can change polarity as its dielectric constant is altered. Thus, water can solubilize a wide range of compounds of both medium and low polarity [39,49].…”

“…By means of high pressure, the boiling point of solvents is increased. As a result, when temperature is high, solvents remain liquid and have better extraction and mass-transfer properties [39]. Therefore, a combination of high pressure and temperature can allow a quick and efficient extraction (5-30 min), with the amount of solvent consumed being dramatically reduced by up to 90% [40].…”