EUBCE 2026 - Stergios VAKALIS - Solvothermal Extraction of Phenolic Compounds and Antioxidants from Spent Coffee Grounds

Solvothermal Extraction of Phenolic Compounds and Antioxidants from Spent Coffee Grounds

Short Introductive summary

Spent coffee grounds are produced in massive quantities worldwide and are typically treated as waste, despite containing significant amounts of valuable bioactive compounds. This study demonstrates how targeted process intensification can transform spent coffee grounds into a high-value source of phenolic compounds and antioxidants. Three extraction techniques—ultrasonic bath, mechanical shaking, and hydrothermal (solvothermal) treatment—were systematically compared using methanol, ethanol, and water as solvents. While ultrasonic extraction at 45 °C achieved rapid recovery, yielding up to 1,250 mg/ kg of phenolics and 32 % antioxidant activity within 45 minutes, hydrothermal extraction at 120 °C delivered a step-change in performance. Under optimized conditions (120 min), total phenolic content reached 7,700 / kg and antioxidant activity peaked at ~39 % RSA—representing a 6–8-fold increase over conventional methods. These results highlight that moderate-temperature solvothermal processing can unlock strongly bound antioxidants from coffee residues, repositioning spent coffee grounds from a disposal problem into a valuable feedstock for bio-based products within circular bioeconomy.

A. Kapetanidis, University of the Aegean, Environment Dpt., Mytilini, GREECE
D. Liakos, National Technical University of Athens, GREECE
S. Vakalis, National Technical University of Athens, GREECE