Interfacial Behavior and Antioxidant Efficiency of Olive Phenolic Compounds in O/W Olive oil Emulsions as Affected by Surface Active Agent Type

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.

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.

Cow milk enriched with nanoencapsulated phenolic extract of jaboticaba (Plinia peruviana)

This study evaluated the total phenolic content (TPC) and the antioxidant activity (AA) of cow's milk enriched with phenolic compounds extracted from jaboticaba peel, either by adding jaboticaba crude extract or a jaboticaba-loaded nanoemulsion. Three nanoemulsions with 5, 10 and 15% of jaboticaba extract were prepared. Average particle diameter (166.7-181.7 nm), polydispersity index (0.138-0.156) and zeta potential (ranging from - 35.30 to - 38.60 mV) were measured for the three different colloidal systems. The nanoemulsion with 15% of jaboticaba extract (J15-NE) was chosen for milk enrichment. J15-NE showed an encapsulation efficiency of 85.6% and remained stable for 60 days at 8 °C. Transmission electron microscopy of J15-NE displayed nanoparticles with a well-defined spherical shape. Reference milk, milk enriched with jaboticaba extract and milk enriched with J15-NE were characterised by a TPC of 93, 171 and 161 µg/ml GAE (gallic acid equivalent), respectively, and an AA of 0.04, 0.17 and 0.14 µg/ml TEAC (trolox equivalent antioxidant capacity), respectively. Thus, this study showed that nanoemulsion with jaboticaba peel extract could be exploited as an ingredient to enrich the properties of milk.

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.

Use of phenolic compounds from olive mill wastewater as valuable ingredients for functional foods

Olive mill wastewater (OMW) is a pollutant by-product from the virgin olive oil production. Its high content in phenolic compounds makes them play an important role for their use in foods, for their high antioxidant significance. The present paper gives an overview on the techniques for OMW valuable ingredient separation, focusing on the most effective ones for their use in food products as functional ingredients. We report on effective methods to recover OMW phenolics, and give several examples on the use these extracts in foods. When added into vegetable oils, their effect on retarding lipid oxidation improves the oxidative status of the product, whilst several challenges need to be faced. OMW phenolic extracts were also used in food emulsions, milk products or other model systems, showing promising results and little or no negative impact on the sensory characteristics or other properties. Their possible use as antimicrobial agents is also another promising approach, as positive results were obtained when applied in meat products. Other examples of using natural phenolic extracts from other sources are suggested also for OMW extracts, to expand their use and thus to improve the nutritional and technological quality of foods.

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

The effect of the surrounding molecular environment (β-lactoglobulin as an emulsion stabilizer and maltodextrin as a viscosity modifier) on the antioxidant activity of three olive oil phenolic compounds (PCs) in olive oil-in-water emulsions was investigated. Oxidation potential, phenolic partitioning, and radical quenching capacity were assessed in solution and in emulsion for oleuropein, hydroxytyrosol, and tyrosol; the influence of β-lactoglobulin and maltodextrin concentration was also evaluated. Finally, the observed properties were related to the oxidative stability of the emulsions containing the PCs to explain their behavior. The order hydroxytyrosol > oleuropein > tyrosol was observed among the antioxidants for both oxidation potential and radical quenching activity. Radical quenching capacity in emulsion and anodic potential were complementary indices of antioxidant effectiveness. As the intrinsic susceptibility of an antioxidant to oxidation expressed by its anodic potential decreased, the environmental conditions (molecular interactions and changes in continuous phase viscosity) played a major role in the antioxidant effectiveness in preventing hydroperoxide decomposition.

Role of olive oil phenolics in physical properties and stability of mayonnaise-like emulsions

The effect of olive oil phenolic content and pattern on the physical properties and stability of olive oil mayonnaise-like emulsions has been investigated. Mayonnaises were formulated with either naturally phenolic-rich extra virgin olive oils or purified olive oil artificially enriched with a phenolic-rich olive extract and pure oleuropein. Mayonnaises were characterized by droplet size distribution, microstructure, textural properties and flow behaviour. The addition of phenolic extracts significantly affected the dispersion degree of the corresponding mayonnaise-like emulsions, their microstructure and physical stability especially in the systems prepared with purified olive oil treated with pure oleuropein and the highest olive phenolic extract concentration. The viscosity and back-extrusion analyses evidenced that the systems characterized by a relatively high content of phenolics, either natural or by addition, presented lower yield stress and viscosity indices and were easier to deform and to break. This study confirms the main role of olive phenolic compounds, and in particular that of oleuropein, in the dispersion state, and physical properties of emulsions with main effects on their quality and stability.

Simulation of oleuropein structural conformation in vacuum, water and triolein-water systems using molecular dynamics

Oleuropein, the main phenolic compound of olive leaves, exhibits a unique blend of biological activities and has been shown to locate itself at the oil-water (O/W) interface. This behavior could influence the physico-chemical properties of dispersed systems such as emulsions. In this work, we study the effect of the microenvironment (vacuum, water, and triolein-water) on the conformational preferences of oleuropein using molecular dynamics (MD) simulations at 300K for at least 30ns. The seven torsions that describe the flexible skeleton of oleuropein were monitored together with the distance between the glucose (Glu) and hydroxytyrosol (Hyd) moieties (d_glu-hyd) of the molecule. The obtained trajectories demonstrated that oleuropein adopts different conformations that depend on the environment. The preferential conformers in each system were analyzed for their molecular geometry and internal energy. In vacuum, the oleuropein preferential conformation is tight with the glucose moiety in close proximity with the hydroxytyrosol moiety. In water, oleuropein preferential conformers presented large differences in their structural properties, varying from a close like U form, and a semi-opened form, to an opened form characterized by high fluctuations in d_glu-hyd values. In a triolein-water system, oleuropein tends to adopt a more open form where the glucose moiety could be approximately aligned with the hydroxytyrosol and elenolic acid moieties. Based on a calculation at the HF/6-31G* level, these flexibilities of oleuropein required energy of 19.14kcal/mol in order to adopt the conformation between water and triolein-water system. A radial distribution function (RDF) analysis showed that specific hydroxyl groups of Hyd and Glu interact with water molecules, enabling us to understand the amphiphilic character of oleuropein at the triolein-water interface. MD calculations together with interfacial tension measurements revealed that the oleuropein binding at O/W interface is an enthalpy driven mechanism.