Statistical optimization and kinetic analysis of the extraction of phenolic compounds from olive leaves

Background Olive leaves are considered to be one of the most abundant agricultural waste source rich in phenolic compounds. A new method for extracting the phenolic compounds contained in olive leaves was developed in this study. The method was based on the addition of sulfuric acid (H2SO4), hydrolyzing the olive leaves and producing extracts rich in phenolic compounds. Experimental runs were carried out according to a central composite design (CCD) comprising the most important factors that affect the extraction process. Results The factors examined were extraction temperature, the addition of H2SO4 and the dilution of olive leaves with water. Maximum total phenolic content (TPC) was 86.4 mg GAE g(-1) dry weight basis (db) at 31.9 degrees C, 6.4% H2SO4 (v/w) and 25.2 L : S (v/w). Validation runs on the optimum were very close to model predictions for TPC. Optimum oleuropein was 43.1 mg g(-1) db at 40 degrees C, 2.0% H2SO4 (v/w) and 30 liquid : solid (v/w). Finally, the kinetics of TPC and oleuropein were studied at the optimum conditions designated by the CCD. Conclusion In this study, a new cost-effective extraction process of phenolic compounds from olive leaves was examined as the developed process employs low-value chemicals (i.e. H2SO4) in small amounts offering through its simplicity the right conditions to scale this process up in industrial applications integrated within olive mill facilities. (c) 2019 Society of Chemical Industry