Comparison of extraction methods for active biomolecules using sub-critical dimethyl ether and n-butane

Several extraction methods are used to isolate natural compounds, and recent approaches utilize subcritical or supercritical extraction media. In this paper we compare extraction methods based on subcritical eluents, dimethyl ether (sC-DME) and n-butane (sC-nB), under mild conditions, using coffee beans and powder as an exemplary raw material. The parameters to be controlled to improve the extraction are considered, and the resulting data discussed. The results obtained display higher selectivity of sC-DME for caffeine (1.9%w/w sC-DME vs. 1.7%w/w sC-nB, on dry extract) and a good yield (0.479 mg/g of caffeine from green coffee beans) compared to, e.g., supercritical carbon dioxide (SC-CO2), which shows 0.32 mg/g of caffeine at higher pressure and temperature (25 MPa, 40 °C). We also discuss some technical implementations for optimizing the use of sub-critical eluents through proper combinations of pressure and temperature. We show that extraction processes based on sub-critical eluents are easy to operate and efficient, and can be easily automated.