title: Optimization of the Aqueous Extraction of Phenolic Compounds from Olive Leaves.
abstract: Olive leaves are an agricultural waste of the olive-oil industry representing up to 10% of the dry weight arriving at olive mills. Disposal of this waste adds additional expense to farmers. Olive leaves have been shown to have a high concentration of phenolic compounds. In an attempt to utilize this waste product for phenolic compounds, we optimized their extraction using water-a "green" extraction solvent that has not yet been investigated for this purpose. Experiments were carried out according to a Box Behnken design, and the best possible combination of temperature, extraction time and sample-to-solvent ratio for the extraction of phenolic compounds with a high antioxidant activity was obtained using RSM; the optimal conditions for the highest yield of phenolic compounds was 90 °C for 70 min at a sample-to-solvent ratio of 1:100 g/mL; however, at 1:60 g/mL, we retained 80% of the total phenolic compounds and maximized antioxidant capacity. Therefore the sample-to-solvent ratio of 1:60 was chosen as optimal and used for further validation. The validation test fell inside the confidence range indicated by the RSM output; hence, the statistical model was trusted. The proposed method is inexpensive, easily up-scaled to industry and shows potential as an additional source of income for olive growers.
authors.affiliation: School of Environmental & Life Sciences, University of Newcastle, Ourimbah, NSW 2258, Australia. chloe.d.goldsmith@uon.edu.au.
authors.forename: Chloe D
authors.initials: CD
authors.lastname: Goldsmith
authors.affiliation: School of Environmental & Life Sciences, University of Newcastle, Ourimbah, NSW 2258, Australia. vanquan.vuong@newcastle.edu.au.
authors.forename: Quan V
authors.initials: QV
authors.lastname: Vuong
authors.affiliation: Faculty of Bioscience Engineering, Ghent University Global Campus, Incheon 406-840, South Korea. costas.stathopoulos@ghent.ac.kr.
authors.forename: Costas E
authors.initials: CE
authors.lastname: Stathopoulos
authors.affiliation: School of Environmental & Life Sciences, University of Newcastle, Ourimbah, NSW 2258, Australia. paul.roach@newcastle.edu.au.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Roach
authors.affiliation: School of Environmental & Life Sciences, University of Newcastle, Ourimbah, NSW 2258, Australia. c.scarlett@newcastle.edu.au.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Scarlett
keywords: Olea europaea; green extraction solvents; olive leaves; phenolic compounds; response surface methodology (RSM); waste valorisation