Antioxidant Behavior of Olive Phenolics in Oil-in-Water Emulsions

Review on the Regulation of Plant Polyphenols on the Stability of Polyunsaturated-Fatty-Acid-Enriched Emulsions: Partitioning Kinetic and Interfacial Engineering

The plant polyphenols are normally presented as natural functional antioxidants, which also possess the potential ability to improve the physicochemical stability of polyunsaturated fatty acid (PUFA)-enriched emulsions by interface engineering. This review discussed the potential effects of polyphenols on the stability of PUFA-enriched emulsions from the perspective of the molecular thermodynamic antioxidative analysis, the kinetic of interfacial partitioning, and the covalent and non-covalent interactions with emulsifiers. Recently, research studies have proven that the interfacial structure of emulsions can be concurrently optimized via promoting interfacial partitioning of polyphenols and further increasing interfacial thickness and strength. Moreover, the applied limitations of polyphenols in PUFA-enriched emulsions were summarized, and then some valuable and constructive viewpoints were put forward in this review to provide guidance for the use of polyphenols in constructing PUFA-enriched emulsions.

A comprehensive review on polarity, partitioning, and interactions of phenolic antioxidants at oil-water interface of food emulsions

There has been a growing interest in developing effective strategies to inhibit lipid oxidation in emulsified food products by utilization of natural phenolic antioxidants owing to their growing popularity over the past decades. However, due to the complexity of emulsified systems, the inhibition mechanism of phenolic antioxidants against lipid oxidation is rather complicated and not yet fully understood. In order to highlight the importance of polarity of phenolic antioxidants in emulsified systems according to the polar paradox, this review covers the recent progress on chemical, enzymatic, and chemoenzymatic lipophilization techniques used to modify the polarity of antioxidants. The partitioning behavior of phenolic antioxidants at the oil-water interface, which can be influenced by the presence of synthetic surfactants and/or antioxidant emulsifiers (e.g., polysaccharides, proteins, and phospholipids), is discussed. In addition, the emerging phenolic antioxidants among phenolic acids, flavonoids, tocopherols, and stilbenes applied in food emulsions are elaborated. As well, the interactions of polar-nonpolar antioxidants are stressed as a promising strategy to induce synergistic interactions at oil-water interface for improved oxidative stability of emulsions.

Radical Scavenging Activity of Olive Oil Phenolic Antioxidants in Oil or Water Phase during the Oxidation of O/W Emulsions: An Oxidomics Approach

Omics approaches are recently being applied also in food lipid oxidation, to increase knowledge of oxidation and antioxidation mechanisms. The so-called oxidomics throws a wider spot of light on the complex patterns of reactions taking place in food lipids, especially in dispersed systems. This research aimed to investigate the radical scavenging activity of olive oil phenolic antioxidants (OPAs) in O/W emulsions, as affected by the phase in which they were added. This allowed one to assess whether different behaviors could be expected from antioxidants originally present in phenolic-rich olive oils compared to natural antioxidants added in the water phase during emulsion production. Hydroperoxide decomposition kinetics and the analysis of volatile pattern provided an outline of antioxidation mechanisms. Though being effective in slowing down oxidation when added both in the oil and water phase, OPAs interfered in different ways with oxidation pathways, based on the phase in which they were added. OPAs added to the water phase were more effective in slowing down hydroperoxide decomposition due to the hydrophilic radical initiator. On the other hand, OPAs present in the oil were more effective in preventing radical propagation, with relevant consequences on the volatile pattern.

UV-Vis Spectroelectrochemistry of Oleuropein, Tyrosol, and p-Coumaric Acid Individually and in an Equimolar Combination. Differences in LC-ESI-MS2 Profiles of Oxidation Products and their Neuroprotective Properties

Major phenolic compounds from olive oil (ArOH-EVOO), oleuropein (Ole), tyrosol (Tyr), and p-coumaric acid (p-Cou), are known for their antioxidant and neuroprotective properties. We previously demonstrated that their combination could potentiate their antioxidant activity in vitro and in cellulo. To further our knowledge of their electron-transfer properties, Ole, Tyr, and p-Cou underwent a spectroelectrochemical study, performed either individually or in equimolar mixtures. Two mixtures (Mix and Mix-seq) were prepared in order to determine whether distinct molecules could arise from their simultaneous or sequential oxidation. The comparison of Liquid Chromatography-Electrospray Ionization-Tandem Mass Spectrometry (LC-ESI-MS2) profiles highlighted the presence of specific oxidized products found in the mixes. We hypothesized that they derived from the dimerization between Tyr and Ole or p-Cou, which have reacted either in their native or oxidized forms. Moreover, Ole regenerates when the Mix undergoes oxidation. Our study also showed significant neuroprotection by oxidized Ole and oxidized Mix against H2O2 toxicity on SK-N-SH cells, after 24 h of treatment with very low concentrations (1 and 5 nM). This suggests the putative relevant role of oxidized Ole products to protect or delay neuronal death.

From by-product to food ingredient: evaluation of compositional and technological properties of olive-leaf phenolic extracts

BACKGROUND

Most olive by-products, like olive leaves, are still undervalued despite their strong potential as a source of healthy and functional components. To exploit their potential use as active ingredients in complex food systems, it is of primary importance the knowledge of their composition and technological functionality which represented the objective of this work.

RESULTS

Phenolic extracts from olive leaves, obtained by extraction with pure water (Eth0) and two different water-ethanol solutions (Eth30, Eth70), were characterized for their composition and technological properties such as water- / oil- holding ability, air/water surface activity, and emulsifying capacity at pH 4.5 and 7. Their chemical stability over time, at constant temperature, was also investigated. The technological properties were affected by extraction media and pH. Phenolic extracts displayed significant surface activity, showing dose-dependent behavior. Surface properties were affected by pH and this result was confirmed by the emulsifying capacity. The extracts showed good oil-holding capacity but limited water-binding capacity. Eth70 showed the highest chemical stability, which was confirmed by the rate parameters obtained by modeling data using a Weibull model.

CONCLUSION

The results of this study highlight that olive leaves extracts can represent a useful ingredient in acidic lipid-containing foods. © 2019 Society of Chemical Industry.

Structure-antioxidant activity relationship of β-cyclodextrin inclusion complexes with olive tyrosol, hydroxytyrosol and oleuropein: Deep insights from X-ray analysis, DFT calculation and DPPH assay

Olives and olive oil, a key food type of the Mediterranean diets, are packed with various important polyphenols including oleuropein (OLE), hydroxytyrosol (HTY) and tyrosol (TYR). OLE and HTY are highly powerful antioxidants and play a prime role in the therapeutics of free radical-related diseases. Their molecular stabilities and antioxidant properties can be improved by cyclodextrin (CD) encapsulation. Here, we present a systematic investigation on the inclusion complexes of β-CD-TYR (1), β-CD-HTY (2) and β-CD-OLE (3) by combined single-crystal structure determination, DFT complete-geometry optimization and DPPH antioxidant assay. X-ray analysis and DFT calculation reveal the preference of inclusion geometry with deep protrusion of the aromatic ring moieties of TYR, HTY and OLE from the β-CD O6-H-side, and the common host-guest stabilization scheme via intermolecular O-H⋯O hydrogen bonding interactions. No polyphenol OH group is shielded in the β-CD cavity, in contrast to the structures of β-CD-tea catechins complexes. The established host-guest O-H⋯O hydrogen bonds help to elevate antioxidant capacities of the olive polyphenols upon β-CD encapsulation. The order of antioxidant activity 2 >3 ≫ 1 based on the DPPH measurement is in fair agreement with their relative thermodynamic stabilities derived from DFT calculation.

Enhanced yield of oleuropein from olive leaves using ultrasound-assisted extraction

The aim of this study was to optimize the extraction of oleuropein from olive leaves through a systematic study of the effects of different parameters of ultrasound-assisted extraction (USAE) on the oleuropein yield, in comparison with conventional maceration extraction. A range of operational parameters were investigated for both conventional maceration extraction and USAE: solvent type, olive leaf mass-to-solvent volume ratio, and extraction time and temperature. Oleuropein yield was determined using high-performance liquid chromatography, with total phenolics content also determined. The optimized conditions (water-ethanol, 30:70 [v/v]; leaf-to-solvent ratio, 1:5 [w/v]; 2 hr; 25°C) provided ~30% greater oleuropein extraction yield compared to conventional maceration extraction. The total phenolics content obtained using the optimized USAE conditions was greater than reported in other studies. USAE is shown to be an efficient alternative to conventional maceration extraction techniques, as not only can it offer increased oleuropein extraction yield, but it also shows a number of particular advantages, such as the possibility of lower volumes of solvent and lower extraction times, with the extraction carried out at lower temperatures.

Effect of light irradiation on the antioxidant stability of oleuropein

The stability of oleuropein, a natural antioxidant from Olea europaea, has been often studied in connection with thermal or enzymatic treatments, but very little is known about the effects of UV light. This work aimed at studying the UV-C effects on oleuropein standard solutions once dissolved in ethanol or water. During irradiation, aliquots were taken and analyzed by a flow injection system equipped with a multi-channel coulometric detector and a high-resolution mass spectrometer. The effects of irradiation were also studied by UV spectroscopy. The results show that oleuropein is relatively stable in water or ethanol, but that under UV-C light undergoes a series of fast decomposition reactions leading to hydroxytyrosol and elenolic acid. Overall, this study provides evidences that the degradation of oleuropein by UV-C light follows a mechanism dependent on the solvent used. Moreover, the solvent affects the resulting redox properties of the solution.

Soft-MS and Computational Mapping of Oleuropein

Olive oil and table olives are rich sources of biophenols, which provides a unique taste, aroma and potential health benefits. Specifically, green olive drupes are enriched with oleuropein, a bioactive biophenol secoiridoid. Olive oil contains hydrolytic derivatives such as hydroxytyrosol, oleacein and elenolate from oleuropein as well as tyrosol and oleocanthal from ligstroside. Biophenol secoiridoids are categorized by the presence of elenoic acid or its derivatives in their molecular structure. Medical studies suggest that olive biophenol secoiridoids could prevent cancer, obesity, osteoporosis, and neurodegeneration. Therefore, understanding the biomolecular dynamics of oleuropein can potentially improve olive-based functional foods and nutraceuticals. This review provides a critical assessment of oleuropein biomolecular mechanism and computational mapping that could contribute to nutrigenomics.