Extraction of Lipids From Spent Coffee Grounds Using Organic Solvents and Supercritical Carbon Dioxide

Abstract

In this work, three extraction methods: Soxhlet, microwave irradiation and ultrasonic irradiation for extraction of lipids from spent coffee grounds were carried out using n‐hexane and petroleum benzene as solvent. Also, supercritical fluid extraction (SFE) using CO2 under different conditions was used for comparison. Different methods of extraction with organic solvents showed significant differences in the extraction yields. However, no significant differences were found when a given method (e.g., microwave irradiation) was applied using different organic solvents. On the other hand, different extraction conditions from the various runs of SFE resulted in significantly different extraction yields, all of which were higher than those of the other extraction methods using organic solvents except the Soxhlet extraction. No significant differences were observed in the fatty acid compositions of the extracted oils using organic solvents. However, the fatty acid compositions of the oils extracted under different conditions of SFE indicated significant differences among several fatty acids. PRACTICAL APPLICATIONS Supercritical fluid extraction (SFE) can be applied as a green technology to the oil extraction of spent coffee grounds (SCGs), as a waste product of the coffee industry, demonstrated in this work. Extraction using supercritical carbon dioxide is a feasible food processing unit operation, and no regulatory hurdles. The extraction yield of oil from SCGs was obtained at 98.14% relative to the Soxhlet extraction. This trend demonstrates that SFE can be a potential candidate for oil production from the waste product of the coffee industry.

Effect of Solvent Extraction Parameters on the Recovery of Oil From Spent Coffee Grounds for Biofuel Production

“…The standard deviations calculated from three experimental repeats are also presented, while the oil contents were achieved with a coffee to solvent ratio of 1:9 w/v after 8 h of extraction. The measured SCG moisture contents are similar to those reported by Kondamudi [10] (18-45% w/w) and Ahangari and Sargolzaei (48% w/w) [6,7,9,10,13,16,26]. The variance of the moisture results can be likely attributed to the different coffee brewing procedures that significantly increase the moisture content of SCGs, however there is not a clear difference between ICG and RCG samples (Table 2).…”

“…In particular, the roasting process only increases the trans FA levels (C18:2ct and C18:2tc) [23]. However, experiments performed by Couto et al, Ahangari and Sargolzaei and Kondamudi et al revealed slightly different SCG oil compositions and suggest that differences can occur [7,12,13].…”

“…Furthermore, SCG oil obtained by Haile, which has a very similar FA profile to oil extracted from ICG1, resulted in biodiesel that was found to be within the standard limits (EN 14214) for parameters including density, kinematic viscosity, iodine value, AV and flash point [6]. The suitability of an oil as a biodiesel feedstock is highly dependent on the FA profile [48], and the relatively high percentage of oleic acid in the coffee oil (9.3-10.2% w/w in oil extracted from ICG1- Table 3) is potentially beneficial for biodiesel production, as the relatively long alkyl chain length with only one double bond results in high oxidative stability and a low melting point [13,49]. On the contrary, the high level of polyunsaturated fatty acids in the obtained coffee oil is a disadvantage for biodiesel production as it is closely related to the oxidation rate and the degradation tendency of the fuel [49][50][51].…”

“…The lipid content of SCGs on a dry weight basis has been found to range between 7 and 27.8% w/w according to previous studies [6][7][8][10][11][12][13][14][15][16][17] and is significant relative to other major biodiesel feedstocks such as rapeseed oil (37-50%), soybean oil (20%) and palm oil (20%) [18]. Coffee oil consists primarily of triglycerides, diglycerides, monoglycerides and FFAs that combined account for 85-90% of the total lipid content and are principally composed of linoleic, palmitic, oleic and stearic acids in decreasing order of magnitude and in proportions not unlike those found in other common edible vegetable oils [6,11,13,16,19].…”

“…Coffee oil consists primarily of triglycerides, diglycerides, monoglycerides and FFAs that combined account for 85-90% of the total lipid content and are principally composed of linoleic, palmitic, oleic and stearic acids in decreasing order of magnitude and in proportions not unlike those found in other common edible vegetable oils [6,11,13,16,19]. The FA composition of the extracted oil is significant as it affects the properties of the derived FAMEs, while the presence of FFAs is a major factor affecting the potential for efficient further processing into biodiesel as high FFA levels increase susceptibility to oxidation, speed up degradation and inhibit alkaline catalyzed transesterification [20][21][22].…”