Optimization of natural deep eutectic solvent composition for ultrasound-assisted extraction of phenolic compound from propolis samples

Propolis is a resinous substance collected by bees rich in bioactive phenolic compounds, which confer medicinal properties, making it highly commercialized. Thus, this study aimed to develop a green method of ultrasound-assisted extraction using a natural deep eutectic solvent (NADES) to determine bioactive phenolic compounds in propolis by HPLC-DAD. A mixture design was conducted to optimize the proportion of components in the NADES synthesis, evaluating the components lactic acid, glucose, and water. The best molar ratio was determined to be 2:1:30. To obtain the optimal experimental conditions for the phenolic compound extraction procedure using NADES, the factors NADES volume and sonication time were evaluated using a Doehlert matrix as the response surface methodology, and the optimal conditions were 3.5 mL and 21 min, respectively. Analytical curves were constructed based on the peak areas of standard solutions of vanillic acid, rutin, gallic acid, trans-cinnamic acid, catechin, syringic acid, d-hydroxybenzoic acid, p-coumaric acid, caffeic acid, chlorogenic acid, ferulic acid, and sinapic acid. The detection limits ranged from 0.09 to 0.4 mg L⁻¹. The method presented good precision and accuracy and was applied to determining 12 phenolic compounds in three propolis samples. Furthermore, the proposed method was evaluated as a green alternative for determining phenolic compounds in propolis samples using AGREE and AGREEprep metrics. The final result of these metrics confirms that this method is aligned with Green Analytical Chemistry (GAC) principles.