Antioxidant Activity and Thermal Stability of Oleuropein and Related Phenolic Compounds of Olive Leaf Extract after Separation and Concentration by Salting-Out-Assisted Cloud Point Extraction

Abstract

A fast, clean, energy-saving, non-toxic method for the stabilization of the antioxidant activity and the improvement of the thermal stability of oleuropein and related phenolic compounds separated from olive leaf extract via salting-out-assisted cloud point extraction (CPE) was developed using Tween 80. The process was based on the decrease of the solubility of polyphenols and the lowering of the cloud point temperature of Tween 80 due to the presence of elevated amounts of sulfates (salting-out) and the separation from the bulk solution with centrifugation. The optimum conditions were chosen based on polyphenols recovery (%), phase volume ratio (Vs/Vw) and concentration factor (Fc). The maximum recovery of polyphenols was in total 95.9%; Vs/Vw was 0.075 and Fc was 15 at the following conditions: pH 2.6, ambient temperature (25 °C), 4% Tween 80 (w/v), 35% Na2SO4 (w/v) and a settling time of 5 min. The total recovery of oleuropein, hydroxytyrosol, luteolin-7-O-glucoside, verbascoside and apigenin-7-O-glucoside, at optimum conditions, was 99.8%, 93.0%, 87.6%, 99.3% and 100.0%, respectively. Polyphenolic compounds entrapped in the surfactant-rich phase (Vs) showed higher thermal stability (activation energy (Ea) 23.8 kJ/mol) compared to non-entrapped ones (Ea 76.5 kJ/mol). The antioxidant activity of separated polyphenols remained unaffected as determined by the 1,1-diphenyl-2-picrylhydrazyl method.

In Vitro Anticoccidial Activity of Olive Pulp (Olea europaea L. var. Chemlal) Extract Against Eimeria Oocysts in Broiler Chickens

“…The OP extract at different concentrations showed a significant antioxidant activity in agreement with those reported by Morelló et al [55] and Moudache et al [56,57]. The results of present study correspond also with those published previously, which demonstrated that the antioxidant activity of plant extracts contains quercetin and oleuropein [58][59][60][61][62][63]. Antioxidant activity is often accompanied by antiviral and antibacterial activities of the phenolics compounds.…”

In situ detoxification of lignocellulosic hydrolysate using a surfactant for butyric acid production by Clostridium tyrobutyricum ATCC 25755

“…After the dehydration process by salting out using Na 2 SO 4 (final concentration at 20 %) for stable phase separation, the centrifugation was performed at 1,500 rpm for 10 min at 25 o C [17]. As a control experiment, the same procedure was performed except Tween80 addition.…”

“…There were no further positive effects of Tween 80 above the CMC. Using cloud point extraction [17], the concentration of free phenolics (not incorporated into micelles) after Tween 80 treatment was measured and compared with the concentrations in the absence of Tween 80. As shown in Supplementary Fig.…”

Oleuropein-Rich Olive Leaf Extracts May Ameliorate Consequences of Glucose-Induced Oxidative Stress in Hep G2 Cells

“…The results are presented in Table 1. [11]. HPLC chromatograms of the extracts (Figure 1) and the data presented in Table 1 reveal that oleuropein is the main phenolic component of the extract.…”