Selective adsorption of oleuropein from olive (Olea europaea) leaf extract using macroporous resin
Extraction, optimization, and adsorption of oleuropein from olive (Olea europaea) leaves were carried out, respectively. Face-centered composite design model was chosen for designing the experimental conditions for extraction of olive leaves through response surface methodology. Olive leaf extract obtained under the optimum conditions was concentrated by several macroporous resins (Amberlites XAD 2, XAD 4, XAD 7HP, and XAD 16). The crude and purified extracts were evaluated according to their total phenolic material (TPM) and oleuropein concentration. XAD 7HP showed the best performance regarding adsorption (91%) and desorption ratio (97%) for oleuropein. Pseudo-first- and second-order and Elovich kinetic models were efficient to represent the experimental data for the adsorption of TPM and oleuropein with high correlation coefficients. Equilibrium data were fitted to Langmuir and Freundlich isotherms at four different temperature values. The antioxidant capacity of the extracts was evaluated with several assays such as Cupric ion reducing antioxidant capacity, 2,2-diphenyl-1-picrylhydrazyl, and 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt.