Recent advances in lipid extraction using green solvents

Green solvents are a new class of solvents mostly known for being environmentally friendly. The main green solvents besides water are organic-based solvents, some ionic liquids (including deep eutectic solvents) and CO2, which is typically used in supercritical conditions (SC-CO2). Recently, organic-based solvents and ionic liquids have been subjected to laboratory testing to estimate their potential as substitutes for fossil solvents in the process of lipid extraction. In the last decade, different pure or combined green solvents and different methodologies have been studied and compared with the standard methodology. Cell disruption of animal, vegetable or microbial samples, dry or wet, is a previous step that has been studied many times in association with extraction efficiency. Combined techniques of rupture and extraction using ultrasound, microwaves or maceration were also employed in the extraction process with green solvents. Other techniques such as pressurized liquid extraction and simultaneous distillation and extraction were also applied, sometimes not only with the objective of extracting more, but also of purifying the obtained product. Lipid extraction was performed mainly with the organic solvents cyclopentyl methyl ether and 2-methyltetrahydrofuran, while ionic liquid extractions were performed mainly with imidazolium-based ionic liquids. The advances obtained in this decade in lipid extraction using these three classes of green solvents were studied and evaluated in this review. Economic viability and future challenges were also analyzed with a view to using these solvents in extraction processes on an industrial scale rather than restricted to the extraction of products with high biological value.