Extraction of diterpenes from spent coffee grounds and encapsulation into polyvinylpyrrolidone particles using supercritical carbon dioxide

In this study, supercritical carbon dioxide (SC-CO₂) was used to extract diterpenes from spent coffee grounds (SCGs) and it is followed by the encapsulation of SCG extract into polyvinylpyrrolidone particles using a supercritical antisolvent crystallization method. In the extraction process using SC-CO₂, the effects of three independent variables–temperature (40‒80°C), pressure (10‒30 MPa), and the ratio of ethanol as a modifier (0%‒10% v/v), on dependent variables: extraction yield and total diterpene content–were investigated using the response surface methodology and Box–Behnken design. The optimal conditions for the extraction yield and total diterpene content were predicted to be 40°C/30 MPa/10% v/v of ethanol and 80°C/25 MPa/6% v/v of ethanol, respectively. Notably, the predicted maximum total diterpene content was 15 times the amount obtained by the Soxhlet method using n-hexane, thereby confirming the selectivity of ethanol-modified SC-CO₂ toward diterpenes. Subsequently, based on the supercritical antisolvent crystallization process, the SCG extract was successfully encapsulated into polyvinylpyrrolidone particles with an average particle size of 140 nm, and the water dispersibility of the SCG extract was enhanced by this encapsulation process. The encapsulation of SCG extract with water-soluble polymers enables the further use of SCG extract in food, cosmetic, and pharmaceutical industries.