engleski

Optimization of Ultrasonic-Assisted Extraction of Major Phenolic Compounds from Olive Leaves (Olea europaea L.) Using Response Surface Methodology

Ultrasound-assisted extraction (UAE) of oleuropein (OLE), verbascoside (VER) and luteolin-4'-O-glucoside (L4OG), as the major phenolics from olive leaves, was optimized using response surface methodology (RSM). A Box-Behnken design (BBD) was used to monitor the effect of different modes of ultrasound operation (pulsed and continuous), liquid-solid (L-S) ratio and sonication time on each phenolic yield. The yield of UAE and conventional solid extraction (CSE) was determined after performing UHPLC-DAD analysis on the extracts. The results suggested that under optimal conditions, the concentrations of OLE, VER, and L4OG were 13.386, 0.363 and 0.527 mg/g dry powdered olive leaves (DPOL), respectively. Verification of experiments was carried out under the modified optimal conditions and the relative errors between the predicted and experimental values were dependent on the examined phenolic compound (OLE 8.63%, VER 11.3% and L4OG 22.48%). In comparison with CSE, UAE improved the yield of OLE, VER and L4OG (32.6%, 41.8%, and 47.5%, respectively after 1 min) at a temperature of 60 oC, an L-S ratio of 15 (v/w), and in the continuous mode of UAE. We demonstrated that the UAE technique is an efficient method for enhancing yields of OLE, VER, and L4OG in olive leaves extracts, while the chosen model was adequate to optimize extraction of major phenolic compounds from olive leaves.

ultrasound-assisted extraction ; response surface methodology ; olive leaves ; oleuropein ; verbascoside and luteolin-4'-O-glucoside

This work was supported by the University of Rijeka under the project number 13.11.1.2.02.