Hydro-Ethanolic Mixtures for the Recovery of Phenols from Mediterranean Plant Materials

The optimization of phenol extraction in hydro-ethanolic mixtures was investigated by using dried samples of aromatic plants ( Salvia fruticosa and Origanum dictamnus L.) and fruit-bearing tree leaves ( Olea europaeae L. and Citrus sinensis L.) as substrates. Four extraction conditions were studied by monitoring the phenolic content and the antioxidant efficacy of the extracts. Temperature and time were the primary factors affecting the extraction yield, while their increase to 60 °C and 8 h, respectively, resulted in enhanced phenols recovery. Extraction equilibrium was obtained for all the determinations only in the case of dictamnus after 4 h. The sample/solvent ratio seem to affect conversely the phenol content and antioxidant efficacy (AE) yield, as the higher total phenols concentrations were followed by lower AE values. The ethanol content affected also the process, but the impact on yield was rather important (and negative) only by using absolute ethanol. Sage was the most phenol rich substrate with a maximum yield of 73.3 mg total phenols/g and AE value of 30.6 mg 2,2-diphenyl-1-picrylhydrazyl (DPPH)/g, which were obtained by using the conditions of 40 °C, 8 h, 40 g sample/L, and 70 mL ethanol/100 mL. Dictamnus, olive, and orange tree leaves followed with maximum yields of 43.9, 43.3, and 12.2 mg total phenols/g as well as 16.1, 19.3, and 1.2 mg DPPH/g, respectively (obtained with 40 °C, 2 h, 40 g/L, 70 mL/100 mL, 40 °C, 8 h, 40 g/L, 70 mL/100 mL, and 60 °C, 2 h, 40 g/L, 70 mL/100 mL, respectively). The aromatic plants extracts were proposed as additives in order to produce potable drinks with similar AE to established beverages, after a simple dilution with water.