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

Abstract

The 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 ultrahigh-performance liquid chromatography with a diode-array detector (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 of 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 yields of OLE, VER, and L4OG (32.6%, 41.8%, and 47.5%, respectively, after 1 min) at a temperature of 60 °C, 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-leaf extracts, while the chosen model was adequate to optimize the extraction of major phenolic compounds from olive leaves.

Optimization of Oleuropein and Luteolin-7-O-Glucoside Extraction from Olive Leaves by Ultrasound-Assisted Technology

“…A simultaneous numerical optimization of the experimental conditions for all of responses was carried out using the optimization option in Design Expert software to maximize the responses what generated as optimal conditions of increment of temperature and amplitude of 40 °C (corresponding to a maximum temperature of 60 °C) and 30% (minimum amplitude), respectively (Table 4). Other researchers have also proven that the maximum oleuropein content is obtained at an extraction optimal temperature of 60 °C [33,39]. Using optimal conditions, the maxima response values R, TPC, TFC, DPPH, oleuropein and luteolin-7-glucoside contents, and time were theoretically calculated ( Table 4).…”

“…Extraction procedure is a very important stage for the recovery and isolation of bioactive compounds from olive leaves. Although the effect of UAE operating conditions on the extraction yield, total phenolic and flavonoid contents, and antioxidant capacity has been studied, few works have reported the influence of extraction factors on the recovery of specific phenolic compounds from olive leaves [23,25,33] using UAE and RSM, at least from our knowledge of literature, and only one of them tackled the task of how to simultaneously optimize the recovery of some of the main phenolic compounds found in olive leaves extracts (verbascoside and luteolin-4'-O-glucoside) besides oleuropein, but without taking into account amplitude as a factor to study [39]. In order to obtain the maximum extraction yield of oleuropein and luteolin-7-glucoside, two of the key factors involved in the UAE technique such as the increment of temperature, or maximum operating temperature, and amplitude were examined in this study.…”

“…Using optimal conditions, the maxima response values R, TPC, TFC, DPPH, oleuropein and luteolin-7-glucoside contents, and time were theoretically calculated ( Table 4). The use of temperatures over the optimum should be avoided owing to the fact they lead to solvent loss by evaporation and may also promote degradation of the compounds of interest which has been reported at higher temperatures and therefore for longer periods of time Other researchers have also proven that the maximum oleuropein content is obtained at an extraction optimal temperature of 60 • C [33,39]. Using optimal conditions, the maxima response values R, TPC, TFC, DPPH, oleuropein and luteolin-7-glucoside contents, and time were theoretically calculated ( Table 4).…”

Extraction Techniques of Phenolic Compounds from Plants

“…Generally, for the separation and quantification of phenolic compounds, the HPLC is preferred than gas chromatography (GC). Various factors can effect to the efficiency of HPLC which include sample purification, mobile phase, column types, and detectors [33]. Various literatures have been published regarding purifying and quantifying phenolic compounds using HPLC technique [49,68].…”

Optimisation of ultrasonic-assisted extraction of bioactive compounds from chokeberry pomace using response surface methodology

“…They allow different valuable polyphenolic compounds of great scientific and commercial importance to be discovered. Ultrasound can be treated as a highly efficient technique to be implemented in the food industry because of high reproducibility, short duration, reduction of the processing costs, simplifying manipulation and work-up, higher purity of the final product and low energy consumption (Giacometti et al, 2018).…”