Extraction of phenolic compounds from olive pomace by using natural deep eutectic solvents and innovative extraction techniques

Natural deep eutectic solvents (NADESs) [choline chloride with citric acid (DES-CA), lactic acid (DES-LA), maltose (DES-MA) and glycerol (DES-GLY) and an addition of 20% v/v water in the NADES solutions] combined with homogenate - (HAE), microwave - (MAE), ultrasound - (UAE) or high hydrostatic pressure - (HHPAE) assisted extractions were first successfully applied to phenolic compounds recovery from olive pomace. DES-CA and DES-LA showed the best extraction efficiency in terms of the total phenolic content and the antioxidant activity of the extracts obtained by HAE and UAE and by MAE and HHPAE, respectively. HAE proved to be the best method with extraction efficiency superior to MAE, UAE and HHPAE. HPLC analysis revealed that almost all NADESs obtained extracts were more enriched in phenolic compounds than those with conventional solvents. The results confirmed that the proposed combined methods could provide an excellent alternative for sustainable and green extraction of phenolic compounds from plant sources leading to novel industrial applications.