The role of heating step in microwave-assisted extraction of polyphenols from spent coffee grounds

Microwave-assisted extraction is currently one of the most studied techniques for biomolecule recovery from natural sources, due to its favorable features for the treatment of thermo-sensitive compounds. In this work, the kinetic of antioxidant extraction from spent coffee grounds was investigated, focusing the attention on the effects of initial thermal ramp on the total polyphenol concentration, total solids and antiradical power of the final product. The hydro-alcoholic extracts demonstrated to be very rich of antioxidants with high antiradical power (from 0.45 to 0.88 mu(Tnolox equivalentig/)g(dried spent coffee grounds)), and their quality was significantly affected by the investigated variables. Peleg's model, was successfully used to describe extraction kinetics, whose investigation revealed that 10 min of heating time at 423 K provided the highest concentration of polyphenols, and resulted as a good compromise to perform a fast extraction with high extraction yields (43 mg(caffeic Acid Equivalent)/g(dried spent coffee grounds )after 60 min of extraction). (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.