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This review discusses the application of oleogel technology in emulsified systems. In these systems of mimetic fats, water-in-oil or oil-in-water emulsions can be obtained, but, here, we cover emulsions with an oil continuous phase in detail. Depending on the percentage of water added to the oleogels, systems with different textures and rheological properties can be developed. These properties are affected by the characteristics and concentration of the added components and emulsion preparation methods. In addition, some gelators exhibit interfacial properties, resulting in more stable emulsions than those of conventional emulsions. Oleogel-based emulsion are differentiated by continuous and dispersed phases and the structuring/emulsification components. Crucially, these emulsions could be applied by the food industry for preparing, for example, meat products and margarines, as well as by the cosmetics industry. We present the different processes of emulsion elaboration, the main gelators used, the influence of the water content on the structuring of water-in-oleogel emulsions, and the structuring mechanisms (Pickering, network, and combined Pickering and network stabilization). Finally, we highlight the applications of these systems as alternatives for reducing processed food lipid content and saturated fat levels., (© 2021 Institute of Food Technologists®.)

The rheology of oil-in-water (O/W) emulsions, stabilized and thickened by cellulose nanocrystals, also referred to as nanocrystalline cellulose (NCC), was investigated over broad ranges of NCC and oil concentrations. The NCC concentration was varied from 1.03 to 7.41 wt% based on the aqueous phase. The oil concentration of the emulsion was varied from approximately 10 to 70 wt%. The emulsions produced were highly stable with respect to creaming and coalescence. The emulsions were non-Newtonian in that they exhibited strong shear-thinning behavior. The rheological data were described adequately by a power-law model. The consistency index (K) and the flow behavior index (n) of the emulsions were strongly dependent on the NCC and oil concentrations. At a fixed oil concentration, the consistency index increased whereas the flow behavior index decreased with the increase in NCC concentration. A similar behavior was observed when the NCC concentration was fixed and the oil concentration was increased; that is, the consistency index increased whereas the flow behavior index decreased. [ABSTRACT FROM AUTHOR]

Emulsion systems are prevalent components in food formulation, and researchers have engaged in enhancing their functionality and stability through the application of interfacial engineering methods. Layer-by-Layer (LBL) deposition represents a technique applicable to the oil-water interface, which have been widely employed for improving the stability of emulsion systems through the formation of thick interfacial membranes and the modification of interactions between droplets. By strategically designing the interface with diverse biopolymers, it is possible to synthesize multilayer emulsions that exhibit specialized functions. In this review, recent advances in the preparation of multilayer emulsions and Pickering emulsions via LBL technology were highlighted, with an emphasis on their stabilization and rheological properties. It discussed some research focused on comparable analysis of binary polymer-stabilized emulsion via different interfacial assembly, with the aim of understanding the influence of interfacial properties on the performance and functionality of these emulsion systems. Finally, their promising applications including forming gel structures, delaying lipid digestion, working as specific delivery systems, and acting as template to design novel materials were also summarized. Through strategic modification of their interfacial properties, it is possible to induce a transformation in the rheological behavior of emulsion systems, from a liquid-like state to solid-like gels. By designing the interface via LBL deposition, the emulsions with thicker and special interfacial membrane could be utilized to formulate food-based emulsions with high stability and functionality. [Display omitted] • Layer-by-layer (LBL) deposition at the oil-water interface enhances the stability of emulsions. • Multilayer-coated droplets can be rationally designed by manipulating experimental parameters. • The interaction between droplets and the interfacial layer affects the rheology of LBL emulsions. • Emulsion gels can be induced by controllable bridging flocculation using LBL deposition. [ABSTRACT FROM AUTHOR]

The rheology of oil-in-water (O/W) emulsions, stabilized and thickened by cellulose nanocrystals, also referred to as nanocrystalline cellulose (NCC), was investigated over broad ranges of NCC and oil concentrations. The NCC concentration was varied from 1.03 to 7.41 wt% based on the aqueous phase. The oil concentration of the emulsion was varied from approximately 10 to 70 wt%. The emulsions produced were highly stable with respect to creaming and coalescence. The emulsions were non-Newtonian in that they exhibited strong shear-thinning behavior. The rheological data were described adequately by a power-law model. The consistency index (K) and the flow behavior index (n) of the emulsions were strongly dependent on the NCC and oil concentrations. At a fixed oil concentration, the consistency index increased whereas the flow behavior index decreased with the increase in NCC concentration. A similar behavior was observed when the NCC concentration was fixed and the oil concentration was increased; that is, the consistency index increased whereas the flow behavior index decreased.

The distribution of particles in Pickering emulsions can be estimated through a percolation-type approach coupled to the evolution of their rheological features with the dispersed phase volume fraction ϕ. The rheological behavior of water-in-dodecane Pickering emulsions stabilized with hydrophobic silica nanoparticles is addressed. The emulsions viscosity and elastic modulus are investigated at ϕ varying from 0.1 to 0.75. Various rheological models are adjusted to the experimental data. The comparison of the elastic modulus evolution of the Pickering emulsions with those of emulsions stabilized with surfactants confirms a major contribution of the particles to the rheological behavior of Pickering emulsions and supports the existence of a three-dimensional network between the droplets. The applied percolation approach allows to quantitively estimate a nanoparticles viscoelastic link between the droplets and opposes the classic vision of interfacial monolayers stabilizing the Pickering emulsions. This network of interconnected particles and droplets contributes significantly to the viscosity as well as the elastic modulus of these emulsions. To our knowledge, the applied percolation-based model is the only one capable of providing a structural explanation while describing the abrupt viscosity and elastic modulus growth of Pickering emulsions across the range of ϕ. [ABSTRACT FROM AUTHOR]

Emulsions stabilized by solid nanoparticles, referred to as Pickering emulsions, are becoming increasingly important in applications as they are free of surfactants. However, the bulk properties and stability of Pickering emulsions are far from being well understood. In this work, the rheological behavior and catastrophic phase inversion of emulsions in the presence of starch nanoparticles were studied using in-situ measurements of viscosity and electrical conductivity. The aqueous phase consisting of starch nanoparticles was added sequentially in increments of 5% vol. to the oil phase under agitation condition to prepare the emulsions. The emulsions were water-in-oil (W/O) type at low to moderate concentrations of aqueous phase. At a certain critical volume fraction of aqueous phase, catastrophic phase inversion of W/O emulsion to oil-in-water (O/W) emulsion took place accompanied a sharp jump in the electrical conductivity and a sharp drop in the emulsion viscosity. The W/O emulsions were nearly Newtonian at low concentrations of aqueous phase. At high concentrations of aqueous phase, prior to phase inversion, theW/O emulsions exhibited a shear-thickening behavior. The O/Wemulsions produced after phase inversion were shear-thinning in nature. The comparison of the experimental viscosity data with the predictions of emulsion viscosity model revealed only partial coverage of droplet surfaces with nanoparticles. With the increase in the concentration of starch nanoparticles (SNPs) in the aqueous phase of the emulsions, the phase inversion of W/O emulsion to O/W emulsion was delayed to higher volume fraction of aqueous phase. Thus SNPs imparted some stability to W/O emulsions against coalescence and phase inversion. [ABSTRACT FROM AUTHOR]

Liquid foam exhibits remarkable rheological behavior although it is made with simple fluids: it behaves similar to a solid at low shear stress but flows similar to a liquid above a critical shear stress. Such properties, which have been proved to be useful for many applications, are even enhanced by adding solid particles. Depending on their hydrophobicity and size, the particles can have different geometrical configurations at the mesoscopic scale, that is, at the air–liquid interfaces, in the films, or in the interstices between the bubbles. In this review, we present rheological studies performed on granular rafts and films, on spherical armored interfaces, on gas marbles, and on aqueous foams laden with hydrophilic grains. Image 1 [ABSTRACT FROM AUTHOR]

An in-situ method of measuring the viscosity of unstable and stable emulsions on a continuous basis under agitation conditions was developed and utilized to investigate the viscous behaviour of surfactant-stabilized and nanoparticles-stabilized oil-in-water (O/W) emulsions at different volume fractions of the dispersed phase (oil). The stability characteristics (droplet size and phase-separation) of emulsions under quiescent conditions were also determined with the aging of emulsions. Emulsions are Newtonian at low volume fractions of the dispersed phase. At high concentrations of the dispersed phase, emulsions behave as non-Newtonian shear-thinning fluids. The nanoparticles-stabilized (Pickering) emulsions are unstable in comparison with the surfactant-stabilized emulsions. The droplet sizes of Pickering emulsions increase rapidly with aging, whereas the droplet sizes of surfactant-stabilized remain nearly the same over a period of 24 h. However, Pickering emulsions are much more viscous than the surfactant-stabilized emulsions when comparison is made at the same volume fraction of the dispersed phase. [ABSTRACT FROM AUTHOR]

Vegetal by-product powders, such as apple pomace powder, represent an efficient green alternative to conventional emulsifiers to stabilize oil-in-water Pickering emulsions. The natural material being used without purification, its multiple components shall impact differently the emulsion stability and interact with each other. These effects might be either synergic, competitive, or both depending on their ratio. Herein, the co-stabilizing effects of the apple pomace compounds on Pickering emulsions were explored from microscopic to macroscopic scales. The apple pomace powder was first fragmented into several fractions which were characterized (particle sizes, shape and wettability, oil-water surface activity). Emulsions were then prepared by varying the stabilizing material composition using the different fractions obtained from the apple powder. Emulsions properties (droplet size, rheological properties) and stability were monitored over a month. The key role of solid particles in the surface activity of the apple pomace powder was shown by interfacial tension measurements. All particle-stabilized emulsions were stable against coalescence during storage despite high droplet diameters (up to 80 μm) and low surface coverage. Soluble matter and particles show a synergic behavior to stabilize oil-in-water emulsions. The soluble matter drives droplet size whereas insoluble cellulosic particles are responsible for emulsion stability by both Pickering adsorption to the oil droplet and oil droplet trapping in a three-dimensional network. This study provides new insights into the understanding of natural powders stabilizing mechanisms that may lead to a better prediction of the potential of vegetal by-products as stabilizing agents from their chemical composition. [Display omitted] • Solid particles play a key role in the apple pomace powder surface activity. • Interactions between solid particles and apple pomace soluble compounds are either synergistic or competitive depending on their ratio. • Soluble compounds drive the emulsion droplet size at fixed particle content. • Solid particles prevent emulsion coalescence even at very low surface coverage (below 5% of total interfacial areas covered by solid particles). [ABSTRACT FROM AUTHOR]

Emulsions stabilized by solid nanoparticles, referred to as Pickering emulsions, are becoming increasingly important in applications as they are free of surfactants. However, the bulk properties and stability of Pickering emulsions are far from being well understood. In this work, the rheological behavior and catastrophic phase inversion of emulsions in the presence of starch nanoparticles were studied using in-situ measurements of viscosity and electrical conductivity. The aqueous phase consisting of starch nanoparticles was added sequentially in increments of 5% vol. to the oil phase under agitation condition to prepare the emulsions. The emulsions were water-in-oil (W/O) type at low to moderate concentrations of aqueous phase. At a certain critical volume fraction of aqueous phase, catastrophic phase inversion of W/O emulsion to oil-in-water (O/W) emulsion took place accompanied a sharp jump in the electrical conductivity and a sharp drop in the emulsion viscosity. The W/O emulsions were nearly Newtonian at low concentrations of aqueous phase. At high concentrations of aqueous phase, prior to phase inversion, the W/O emulsions exhibited a shear-thickening behavior. The O/W emulsions produced after phase inversion were shear-thinning in nature. The comparison of the experimental viscosity data with the predictions of emulsion viscosity model revealed only partial coverage of droplet surfaces with nanoparticles. With the increase in the concentration of starch nanoparticles (SNPs) in the aqueous phase of the emulsions, the phase inversion of W/O emulsion to O/W emulsion was delayed to higher volume fraction of aqueous phase. Thus SNPs imparted some stability to W/O emulsions against coalescence and phase inversion.

An in-situ method of measuring the viscosity of unstable and stable emulsions on a continuous basis under agitation conditions was developed and utilized to investigate the viscous behaviour of surfactant-stabilized and nanoparticles-stabilized oil-in-water (O/W) emulsions at different volume fractions of the dispersed phase (oil). The stability characteristics (droplet size and phase-separation) of emulsions under quiescent conditions were also determined with the aging of emulsions. Emulsions are Newtonian at low volume fractions of the dispersed phase. At high concentrations of the dispersed phase, emulsions behave as non-Newtonian shear-thinning fluids. The nanoparticles-stabilized (Pickering) emulsions are unstable in comparison with the surfactant-stabilized emulsions. The droplet sizes of Pickering emulsions increase rapidly with aging, whereas the droplet sizes of surfactant-stabilized remain nearly the same over a period of 24 h. However, Pickering emulsions are much more viscous than the surfactant-stabilized emulsions when comparison is made at the same volume fraction of the dispersed phase.

Lactobacillus dellbrueckii cultured in MRS and harvested in the late log phase was entrapped in the inner aqueous phase of a water-in-oil-in-water (W 1 /O/W 2 ) Pickering emulsion stabilized by inclusion complexes having d 32 of 3.6 μm formed from β-cyclodextrin (β-CD) and the results were compared to the corresponding double emulsions with Tween-80 as the secondary emulsifier. The stability of emulsions prepared at various primary emulsion contents and emulsifier concentrations was investigated. Emulsion morphology was observed by polarization microscopy and size distributions of dispersed droplets were examined to establish emulsion stability. The solid-like property of the test W 1 /O/W 2 emulsions was found to dominate based on the oscillatory experiments results (G′>G″). The precipitated fraction obtained upon centrifugation of the emulsion phase was structurally characterized using 1 H nuclear magnetic resonance (NMR) spectroscopy and scanning electron microscopy (SEM) and the solid inclusion complex formation between β-CD and double emulsion contents was confirmed. The existence of L. dellbrueckii in β-CD containing emulsions was evidenced by Fourier transform infrared (FTIR) spectroscopy in ATR geometry and fluorescence microscopy. Moreover, the survival of the entrapped cells (initial number = 8.17 log CFU/ml) increased significantly with use of β-CD compared to Tween-80. It is concluded that the double emulsion prepared using β-CD protected L. dellbrueckii and the experimental findings of the present study are a fundamental guide for practical applications in food industry. [ABSTRACT FROM AUTHOR]

The relationship between interfacial and bulk emulsion viscoelasticity is investigated. Water-in-dodecane reverse Pickering emulsions, with a dispersed phase volume fraction of 0.66, stabilized with partially hydrophobic silica particles are addressed. Interfacial and bulk viscoelastic properties are probed via 2D and 3D oscillatory shear rheology. The silica particles concentration and NaCl content have been varied. In the whole range of concentrations studied the elastic modulus (G′) remains always greater than the viscous modulus for 2D and 3D rheology. The viscoelastic behavior can be related to the silica concentration both at the interface and in the emulsion. Power law dependences towards the silica content are recorded for the interfacial and the bulk emulsion elastic modulus. When increasing the NaCl concentration, the viscoelastic properties both at the interface and in the emulsion become stronger. The amount of silica and NaCl produces similar effects on both the interface and bulk viscoelastic properties. The increase of their concentration induces a rigidification of the dodecane/water interface since G P ′ (interface) increases. Such interfacial hardening produces a rigidification of the droplets ( G P ′ (Emulsion) is enhanced). Correlations between the interfacial and bulk emulsion viscoelasticity are also extracted from the experimental data. This is the first time that these kinds of relationship are reported. These results highlight that everything that affects the interfacial viscoelasticity is reflected on the bulk scale of emulsions. [Display omitted] [ABSTRACT FROM AUTHOR]