Extracting bioactive compounds from natural products for cosmetics, pharmaceuticals, and health supplements is challenging due to concerns over solvent toxicity, environmental impact, and energy consumption. Conventional extraction methods, such as hexane, water/ethanol mixtures, supercritical water, and supercritical carbon dioxide (SC-CO₂), each have limitations. Hexane extraction requires energy-intensive moisture removal and raises concerns about residual toxicity. Extraction with water/ethanol mixtures is safer but inefficient for nonpolar compounds and requires significant energy for ethanol recovery. Moreover, supercritical water extraction can degrade heat-sensitive compounds and complicate the purification process, while SC-CO₂ struggles with polar compound solubility, necessitating additional drying steps.
To address these issues, this study explores liquefied dimethyl ether (L-DME) as an alternative solvent for extracting bioactive and lipid-based compounds from wet tangerine pomace (TP) and spent coffee grounds (SCG). L-DME has unique properties, including slight polarity, excellent solubility in both water and lipids, low surface tension, and high penetration ability. Unlike conventional methods, L-DME extraction removes water while simultaneously extracting valuable compounds under mild conditions, reducing energy consumption and minimizing solvent residues. Recognized as a food-grade solvent in the United States, Europe, and New Zealand, DME is suitable for applications in biofuels, food, and cosmetics.
This study developed and optimized an L-DME extraction process to efficiently recover fine chemicals from TP for cosmetic and other high-value applications. The research covered four key areas: (1) process development, (2) utilization of extraction residues, (3) scale-up, and (4) development of functional cosmetic ingredients. L-DME extraction effectively separated lipid- and water-soluble bioactive compounds, offering a high-yield, energy-efficient alternative to conventional methods.
Additionally, SCG was investigated as a renewable feedstock for biofuel and functional ingredient production. SCG, a byproduct of coffee brewing, contains valuable compounds such as lipids, antioxidants, caffeine, and sugars. L-DME extraction was performed under various conditions (temperatures: 25–55 °C, pressures: 2–4 MPa, and DME consumption: 400–1200 mL) to optimize total extract yield, fatty acid recovery, and bioactive compound extraction. The process efficiently removed 95.9–97.1 wt% of moisture from wet SCG while recovering biocrude rich in fatty acid methyl esters (FAME) (988.4 mg/g), bioactive water-soluble compounds, and dewatered solid residues. The extracted water fraction contained high levels of caffeine (93.44 mg/g dry extract) and total phenolics (225.0 mg GAE/g dry extract), highlighting its potential for food and cosmetic applications. Elemental analyses of the biocrude and solid residues confirmed their suitability for biofuel production. Compared to conventional Soxhlet extraction, L-DME extraction demonstrated superior efficiency in recovering bioactive compounds while eliminating the need for energy-intensive drying.
Overall, this study highlights L-DME extraction as a green, energy-efficient, and scalable method for directly recovering valuable compounds from wet biomass such as TP and SCG. The process not only enhances the extraction of high-value ingredients for biofuels, cosmetics, food, and pharmaceuticals but also contributes to the sustainable utilization of agricultural and food waste resources.