Choline chloride derivative-based deep eutectic liquids as novel green alternative solvents for extraction of phenolic compounds from olive leaf

In the presented study, a new methodology based on the use of deep eutectic solvents (DESs) and microwave-assisted extraction (MAE) and subsequent analysis by HPLC-DAD-ESITOF- MS was proposed for the extraction of phenolic compounds from olive leaf. Nine different DESs, using choline chloride as hydrogen bond acceptor in combination with different hydrogen bond donors (four polyalcohols, three organic acids, one sugar and urea), were firstly scanned. A total of 48 phenolic compounds were identified in the olive leaf using HPLC-DAD-ESI-TOF-MS. Experimental results and multivariate data analysis pointed to choline chloride-ethyleneglycol as being the most effective within the tested DESs, showing extraction yields similar to those exhibited by conventional solvents. A Box-Behnken Design and response surface methodology were applied with the aim to optimize the main parameters involved in the extraction process. The optimal extraction conditions were 79.6 ºC of temperature, 43.3% of water and 16.7 min of irradiation time. Correlation coefficients (R2> 0.98) indicated a good relationship between experimental data and the fitted quadratic term models. Results indicated that DESs could be a sustainable alternative to traditional solvents for the extraction of bioactive compounds among many other applications.Thanks to the Spanish Ministry of Economy and Competitiveness (MINECO) (AGL2015-67995-C3-2-R) and the Andalusian Regional Government Council (P11-CTS-7625). M.E. Alañón also thanks to Ministry of Education and Competitiveness for the postdoctoral contract Juan de la Cierva-Incorporación (IJCI-2014-21664)