Olive Tree (Olea europeae L.) Leaves: Importance and Advances in the Analysis of Phenolic Compounds
Abstract
:1. Olive Leaves as a Potential Source of Phenolic Compounds
2. Sample Preparation
Objectives of the Research | Drying Process and Conditions | Reference |
---|---|---|
Study the effect of blanching and/or infrared drying on the color, total phenols content and the moisture removal rate of four olive leaf varieties | Infrared dryer Infrared drying temperatures: 40, 50, 60 and 70 °C | [29] |
Investigate the main effects of process variables on the product quality during heat pump drying of olive leaves Determine an optimum process conditions for drying of olive leaves in a pilot scale heat pump conveyor dryer | Pilot scale heat pump conveyor dryer Drying air temperature range: 45–55 °C Drying air velocity range: 0.5–1.5 m/s Time range: 270–390 min | [30] |
Investigate the main effects of process variables on the product quality during hot air drying of olive leaves Determine an optimum process conditions for drying of olive leaves in a tray drier | Laboratory-type tray dryer Drying compartment dimensions: 0.3 × 0.3 × 0.4 m Drying air temperatures: 40–60 °C Drying air velocities: 0.5–1.5 m/s Process time: 240–480 min | [31] |
Study the influence of the ultrasound power application during the drying of olive leaves in the kinetics of process | Pilot scale convective dryer modified to apply power ultrasound Drying temperature: 40 °C Air velocity: 1 m/s Levels of electrical power applied to the ultrasound transducer: 0, 20, 40, 60 and 80 W Ultrasonic power density in drying chamber: 0, 8, 16, 25 and 33 kW/m3 | [27] |
Determine and test the most appropriate thin-layer drying model. Reveal the effects of drying air temperature and velocity on the effective diffusion coefficient and activation energy for understanding the drying behavior of olive leaves | Thin-layer dryer Drying air temperatures: 50, 60 or 70 °C Drying air velocities: 0.5, 1.0 or 1.5 m/s | [28] |
Investigate the effect of solar drying conditions on the drying time and some quality parameters of olive leaves particularly the color, total phenol content and radical scavenging activity | Laboratory convective Solar Dryer Drying air temperatures: 40, 50 and 60 °C Drying air velocities: 1.6 and 3.3 m3/min | [26] |
Develop a direct and rapid tool to discriminate five Tunisian cultivars according to their olive leaves by using FT-MIR spectroscopy associated to chemometric treatment | Microwave Two times for 2 min Maximum power 800 W (2450 MHz) | [32] |
Study the effect of freezing and drying of olive leaves on the antioxidant potential of extracts Choose an appropriate drying process to obtain extracts rich in bioactive compounds | -
Hot air drying by forced air laboratory dryer 70 °C for 50 min and at 120 °C for 12 min Air flow: 0.094 m3/s Air velocity: 0.683 m/s -Freeze air drying by freeze dryer chamber Initial temperature: −48 ± 2 °C, shelf temperature set at 22 ± 2 °C. Time: 48 h and Pressure: 1.4 × 10−1 mbar | [33] |
3. Extraction Procedures
Extraction Technique | Analytical Technique | Observations | Reference |
---|---|---|---|
Extractant solvents: ethanol, methanol, acetone and their aqueous form (10%–90%, v/v). Extraction time: 24 h | HPLC-UV (280 nm) Stationary phase: C18 Lichrospher 100 analytical column (250 × 4 mm, 5 μm) at 30 °C Flow rate:1 mL/min Mobile phases: acetic acid/water (2.5:97.5) (A)and acetonitrile (B) Elution: gradient Total time: 60 min | 70% ethanol as extractant solvent for high content of phenolics and antioxidant capacity. oleuropein (13.4%), rutin (0.18%). Silk fibroin was found to be a promising adsorbent for the purification of oleuropein and rutin from olive leaf extracts | [38] |
30–50 mg of olive leaves powder | Mid-Infrared Spectroscopy Mid-infrared spectra were recorded between 4000 cm−1 and 700 cm−1 Nominal resolution was 4 cm−1 | Mid-infrared spectroscopy, as a rapid tool, to predict oleuropein content in olive leaf from five Tunisian cultivars (Chemlali, Chetoui, Meski, Sayali and Zarrazi) Oleuropein: 8.72% and 17.95% | [34] |
0.5 g of dry leaves extracted via Ultra-Turrax 10 mL of MeOH/H2O (80/20) Ultrasonic bath (10 min) Extraction repeated twice | HPLC-DAD-ESI-TOF- MS Stationary phase: Poroshell 120 EC-C18 analytical column (4.6 × 100 mm, 2.7 μm) (Agilent Technologies, CA, USA) Mobile phases: acidified in water (acetic acid 1%) (phase A) and acetonitrile (phase B) Elution: gradient Flow rate: 0.8 mL/min | 30 phenolic compounds were identified. Total phenolic compounds: 52.12–60.64 mg/kg | [39] |
Fresh leaves in aqueous methanol 80% | HPLC-DAD (240, 254, 280, 330 and 350 nm) MS (MSD API-electro spray) and NMR Stationary phase: Zorbax Stablebond SB-C18 column (5 µm; 250 × 4.6 mm (Agilent Technologies, Palo Alto, CA, USA) Mobile phases: acidified water (pH 3.2 by formic acid (A)), methanol (B) and acetonitrile (C) Elution: gradient Flow rate: 0.8 mL/min | Novel secoiridoid glucosides identified as a physiological response to nutrient stress | [40] |
MAE 1.25 g of milled fresh olive leaves, 10 mL of methanol, ethanol and their aqueous form (40%–100%). Extraction time: 4–16 min, Irradiation temperature: 10–120 °C. | HPLC-ESI-TOF/IT-MS Stationary phase: C18 Eclipse Plus analytical column, Agilent Technologies, CA, USA) (4.6 × 150 mm, 1.8 μm) at 25 °C, Mobile phases: acetic acid (0.5%) (A) and acetonitrile (B) Elution: gradient Flow rate 0.8 mL/min | Univariate optimisation for phenolics extraction: methanol: water (80%) at 80 °C for 6 min 36 compounds | [41] |
MAE Power 100–200 W, irradiation time 5–15 min, ethanol 80%–100% | HPLC-DAD (280, 330, 340 and 350 nm) Stationary phase: Lichrospher 100 RP18, Análisis Vínicos, Ciudad Real, Spain (250 × 4 mm,5 μm), Kromasil 5 C18 column, Scharlab, Barcelona, Spain (15 × 4.6 mm, 5 μm) Mobile phases: 6% acetic acid, 2 mM sodium acetate, in water (A) and acetonitrile (B) Elution: gradient Flow rate 0.8 mL/min GC-IT-MS # Stationary phase: fused-silica capillary column, Varian, TX, USA (VF-5 ms, 30 m × 0.25 mm, 0.25 μm) | Multivariate optimization for extraction of oleuropein and related biophenols: 200 W for 8 min, ethanol 80%, oleuropein 2.32%, verbacoside 631 mg/kg, apigenin-7-glucoside 1076 mg/kg, luteolin-7-glucoside 1016 mg/kg) Simple phenols were not found in the extracts obtained by MAE | [42] |
USAE solvent concentration: 0–100% ethanol Ratio of solid to solvent: 25–50 mg/mL Extraction time: 20–60 min Frequency: 50 Hz | UV spectrometry (Folin–Ciocalteu) | Multivariate optimization: 50% EtOH, 500 mg dried leaf to 10 mL solvent, and 60 min Solvent concentration was proved to be the most significant parameter of all the parameters used | [43] |
DUSAE (20 kHz, 450 W) Tested variables: probe position: 0–4 cm ultrasound radiation amplitude: 10%–50% Duty cycle: 30%–70% Irradiation time: 6–30 min Extractant flow- rate: 4–6 mL/min Ethanol: 50%–90% Water bath: temperature: 25–40 °C | HPLC–DAD (280, 330, 340 and 350 nm) Stationary phase: Lichrospher 100 RP18 (250 × 4 mm,5 μm), Kromasil 5 C18 column (15 × 4.6 mm, 5 μm) Mobile phases: 6% acetic acid, 2 mM sodium acetate, in water (A) and acetonitrile (B) Elution: gradient Flow rate: 0.8 mL/min GC-IT-MS Stationary phase: fused-silica capillary column (VF-5 ms, 30 m × 0.25 mm, 0.25 μm) Carrier gas: Helium (1 mL/min) Ionisation: electron impact | Multivariate methodology optimization: 1 g of milled leaves in a 59:41 ethanol–water mixture, bath temperature 40 °C, extraction time 25 min, ultrasonic irradiation (duty cycle 0.7 s, output amplitude 30% of the converter, applied power 450 W. Target analytes concentration:oleuropein, verbacoside, apigenin-7-glucoside and luteolin-7-glucoside contents: 22610 ± 632, 488 ± 21, 1072 ± 38 and 970 ± 43 mg/kg; respectively | [44] |
SFE 1 g of milled olive leaves Pressure and temperature: 150 bar and 40 °C Extraction solvent: CO2 + 6.6% of ethanol as modifier Extraction time: 2 h | HPLC-ESI-TOF/IT-MS Stationary phase: C18 Eclipse Plus analytical column (4.6 × 150 mm, 1.8 μm) at 25 °C Mobile phases: acetic acid (0.5%) (A) and acetonitrile (B) Elution: gradient Flow rate 0.8 mL/min | Compared to other extraction techniques MAE, CM and PLE, SFE was the best extraction procedure for apigenin and diosmetin isolation | [45] |
SFE Pressure: 30 MPa Extraction temperature: 50°C Separation temperature: 55°C Mode: dynamic Variables: solvent-to-feed ratio, 120 or 290; co-solvent: 5% or 20% | HPLC-DAD (248 nm) Stationary phase: SupelcoAnalytical Discovery HS C18 (250 × 4.6 mm, 5.0 μm) at 25 °C Mobile phases: H2O + 1% acetic acid (A) and MeOH (B) Elution: gradient Flow rate: 1 mL/min | Pressure: 30 MPa, extraction temperature: 50°C, separation temperature: 55 °C, mode: dynamic, solvent-to-feed ratio: 290, co-solvent: 20% Oleuropein 30% | [46] |
PLE: 1 g of grinded olive leaves Solvent: ethanol or water Pressure 100 bar, temperature 150 °C time Extraction time: 20 min | HPLC-ESI-TOF/IT-MS Stationary phase: C18 Eclipse Plus analytical column (4.6 × 150 mm, 1.8 μm) at 25 °C Mobile phases: acetic acid (0.5%) (A) and acetonitrile (B) Elution: gradient Flow rate 0.8 mL/min MS: negative mode | PLE (using ethanol as solvent) produced the highest yield for all the studied varieties. PLE (using water as solvent) did not show a good efficiency either for extracting oleuropein. | [45] |
PLE Ethanol (150 °C) Water (200 °C) Extraction time: 20 min | HPLC–ESI–QTOF–MS Stationary phase: C18 (3 μm, 2 × 150 mm) at 25 °C Elution: gradient elution program at a flow rate of 0.2 mL/min. The mobile phases consisted of water plus 0.5% acetic acid (A) and acetonitrile (B) MS: negative mode | The first time that lucidumoside C has been detected in olive leaves The ethanolic extract has proven to be especially rich in flavonoids, while the aqueous extract was richer in hydroxytyrosol. | [47] |
PLE 6 g of grinded olive leaves Variables: temperature, static time, extraction cycles and EtOH (%) Pressure 1500 psi | HPLC-DAD (248 nm) Stationary phase: Supelco Analytical Discovery HS C18 (250 × 4.6 mm, 5.0 μm) at 25 °C Mobile phases: H2O + 1% acetic acid (A) and MeOH (B) Mode: gradient Flow rate: 1 mL/min | Multivariate optimization The extraction yield is mainly influenced by 3 factors (in the order of statistical significance): temperature, static time and extraction cycles. The effect is positive in all three cases. oleuropein: 26.1% | [48] |
SHLE Tested variables: temperature, static and dynamic extraction time, extractant flow-rate and extractant composition | HPLC–DAD (280, 330, 340 and 350 nm) Stationary phase: Lichrospher 100 RP18 (250 × 4 mm,5 μm), Kromasil 5 C18 column (15 × 4.6 mm, 5 μm) Mobile phases: 6% acetic acid, 2 mM sodium acetate, in water (A) and acetonitrile (B) Elution: gradient Flow rate: 0.8 mL/min | Multivariate optimization 1 g of leaves , Pressure: 6 bar , 70:30 ethanol–water, temperature 140 °C, 6 min Dynamic mode,extractant for 7 min at 1 mL/min, Extraction time: 13 min 23 g/kg of oleuropein, 665 mg/kg of verbascoside, 1046 mg/kg of apigenin-7-glucoside, 998 mg/kg of luteolin-7-glucoside | [49] |
4. Determination of Phenolic Compounds
5. Exploitation of Bioactive Components
6. Conclusions
Acknowledgments
Conflicts of Interest
References
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Abaza, L.; Taamalli, A.; Nsir, H.; Zarrouk, M. Olive Tree (Olea europeae L.) Leaves: Importance and Advances in the Analysis of Phenolic Compounds. Antioxidants 2015, 4, 682-698. https://doi.org/10.3390/antiox4040682
Abaza L, Taamalli A, Nsir H, Zarrouk M. Olive Tree (Olea europeae L.) Leaves: Importance and Advances in the Analysis of Phenolic Compounds. Antioxidants. 2015; 4(4):682-698. https://doi.org/10.3390/antiox4040682
Chicago/Turabian StyleAbaza, Leila, Amani Taamalli, Houda Nsir, and Mokhtar Zarrouk. 2015. "Olive Tree (Olea europeae L.) Leaves: Importance and Advances in the Analysis of Phenolic Compounds" Antioxidants 4, no. 4: 682-698. https://doi.org/10.3390/antiox4040682
APA StyleAbaza, L., Taamalli, A., Nsir, H., & Zarrouk, M. (2015). Olive Tree (Olea europeae L.) Leaves: Importance and Advances in the Analysis of Phenolic Compounds. Antioxidants, 4(4), 682-698. https://doi.org/10.3390/antiox4040682