Semi-continuous extraction/hydrolysis of spent coffee grounds with subcritical water

Spent coffee grounds (SCG) were treated with subcritical water (SBW) in a semi-continuous reactor at different temperatures, pressures, and water flowrates. Yields of carbohydrates and phenolics reached 33.7 g and 4 g per 100 g-dry SCG, respectively, at 200 degrees C, 70 bar and 10 mL/min. Liquors collected at the beginning of assays were richer in phenolics and poorer in carbohydrates, whose yield increased sharply when temperature reached 150 degrees C. Most carbohydrates were recovered as oligosaccharides, and practically all cellulose remained in the SCG recovered at the end of assays. Extracts exhibited DPPH antioxidant capacity and antibacterial activity against both Gram-positive and Gram-negative bacteria. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.