Caffeine and Polyphenolic Compound Recovery Optimization from Spent Coffee Grounds Utilizing Pressurized Liquid Extraction

Coffee belongs among the most widespread beverages worldwide, and its increasing consumption leads to the generation of a large amount of by-products, mainly spent coffee grounds (SCGs). SCGs can be further recycled as they contain bioactive compounds. This research aims to search for the extraction conditions that lead to the highest recovery of these compounds through a green extraction technique, pressurized liquid extraction (PLE). The parameters studied were solvent composition, temperature, and extraction time, while the pressure was kept constant at 1700 psi. The optimum conditions were 48% v/v ethanol solution at 160 °C for 25 min. Under these conditions, the maximum recoveries were total polyphenol content of 15.99 mg gallic acid equivalents/g dry weight (dw), a total caffeine content of 1.15 mg/g dw, and an antioxidant capacity determined through the ferric-reducing antioxidant power of 101.87 μmol ascorbic acid equivalents/g dw. Additionally, individual polyphenols in SCGs were studied by high-performance liquid chromatography, revealing that the extracts were rich in chlorogenic acid, (−)-epicatechin, and rutin. The results of this work can set the basis for the further utilization of SCGs through PLE by the beverage, food, pharmaceutical, and cosmetic industries.