Recovery of antioxidant polyphenols from olive leaves (Olea europaea spp.) using a novel deep eutectic solvent made of bioorganic molecules
In this study, the extraction of polyphenols from Olea europaea leaves was investigated, using a biomolecule-based deep eutectic solvent (DES), composed of glycerol and the amino acid glycine. The study, which is presented here, describes for the first time the use of an eco-friendly DES as a highly...
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| Main Authors: | , |
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| Other Authors: | |
| Language: | English |
| Published: |
2020
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| Subjects: | |
| Online Access: | http://hdl.handle.net/11610/20641 |
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| Summary: | In this study, the extraction of polyphenols from Olea europaea leaves was investigated, using a biomolecule-based deep eutectic solvent (DES), composed of glycerol and the amino acid glycine. The study, which is presented here, describes for the first time the use of an eco-friendly DES as a highly effective solvent for the extraction of polyphenols from olive tree leaves.
The first part was to optimise DES concentration (CDES) and the liquid-to-solid ratio (RL/S), by employing a Box-Behnken experimental design. Following this, a kinetic assay was undertaken to assess the effect of temperature. Comparative evaluation using 60% ethanol, 60% methanol and water showed that the DES used was significantly more efficient in extracting polyphenols and flavonoids, yielding extracts with higher antiradical activity and reducing power. Liquid chromatography-photodiode array-mass spectrometry (LC-PDA-MS) examination of the DES extract showed that the major polyphenols were luteolin and apigenin glycosides, as well as the secoiridoid derivative oleuropein.
In the second part, it was evaluated the effect of methyl-β-cyclodextrin (m-β-CD) on the efficiency of polyphenol extraction from O. europaea leaves. The process developed was based on a Box-Behnken experimental design and response surface methodology, to assess the simultaneous effect of m-β-CD concentration (Cm-β-CD), liquid-to-solid ratio (RL/S) and temperature (T). The extraction kinetics also showed that the extraction rate was slowed down in the presence of m-β-CD, yet the higher extraction capacity of the DES/m-β-CD medium was confirmed. Characterization of the extracts obtained with DES/m-β-CD and DES by means of LC-PDA-MS demonstrated that there was no selective extraction of any particular polyphenol, suggesting that m-β-CD acted merely as an extraction booster.
In the third part, the stability of the extracts was checked. In particular, the extracts (DES/m-β-CD, DES, 60% ethanol and water) were allowed to stand at 4 °C (cooling temperature), 22 °C (room temperature) and 50 °C (water bath) for 20 days. After this period, the reducing power (PR) was monitored to trace changes in the antioxidant potency of the extracts. Examination of the polyphenolic profiles using LC-PDA-MS showed that after storage for 20 days at 50 °C, some major polyphenols occurring in olive leaves (OLL) suffered extended degradation.
In the fourth and final part, the use of a novel natural DES was studied that enabled the effective extraction of OLL polyphenols and their testing as radical scavengers, in the presence or absence of m-β-CD, using descriptive kinetics. Testing extended to include interactions with ascorbic acid, a natural powerful antioxidant, by implementing response surface methodology. The kinetic study showed that m-β-CD may hinder the radical scavenging effect of OLL extracts, yielding lower stoichiometry upon reaction with the radical probe DPPH. |
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