Green Extraction of Cork Bioactive Compounds Using Natural Deep Eutectic Mixtures

Quercus suber cork generates bioactive components, such as phenolic acids, terpenoids, and tannins, with excellent biological properties, including antioxidant, anti-inflammatory, and antiaging activities. Aiming to design environmentally benign processes to eliminate, or reduce, the use of toxic chemicals, we propose the green extraction of bioactives from cork using natural deep eutectic solvents (NADES). Several deep eutectic mixtures were developed, through the mixture of natural compounds, namely, lactic acid, glycerol, ethylene glycol, sodium citrate, and sodium lactate, chosen according to their origin, toxicity, biocompatibility, polarity, and pH. The results revealed higher extraction yields when using NADES instead of harsh solvents like dioxane, with the extraction process governed by several physical-chemical parameters, including pH, polarity, viscosity, and density, and also by the method of extraction. Acidic NADES composed of lactic acid and glycerol, or sodium citrate, extracted a greater amount of aromatic compounds, terpenoids, and fatty acids and their derivatives. More basic eutectic mixtures, composed of sodium lactate and a polyol (ethylene glycol or glycerol), extracted predominantly low molecular weight polar compounds. The extracts range encompassed by the developed NADES, together with the associated nontoxicity, low price, and ease of preparation, establish these solvents as a green approach to extract high added-value compounds from cork.