Formation Of High Internal Phase Emulsions Research Articles

Modulating the properties of myofibrillar proteins-stabilized high internal phase emulsions using chitosan for enhanced 3D-printed foods

The 3D printability of myofibrillar proteins (MP)-based high internal phase emulsions (HIPEs) is a concern. This study investigated the influence of chitosan (CS) concentrations (0–1.5 wt%) on the physicochemical properties, microstructure, rheological properties, and stability of MP-based HIPEs. Results showed that the interaction between MP and CS efficiently modulated the formation of HIPEs by modifying interfacial tension and network structure. The addition of CS (≤ 0.9 wt%, especially at 0.6 wt%) acted as a spatial barrier, filling the network between droplets, which triggered electrostatic repulsion between CS and MP particles, enhancing MP's interfacial adsorption capacity. Consequently, droplet sizes decreased, emulsion stability increased, and HIPEs became more stable during freeze-thaw cycles, centrifugation, and heat treatment. The rheological analysis further demonstrated that the low energy storage modulus (G', 330.7 Pa) of MP-based HIPEs exhibited sagging and deformation during the self-supporting phase. However, adding CS (0.6 wt%) significantly increased the G' (1034 Pa) of MP-based HIPEs. Conversely, increasing viscosity and spatial resistance attributed to CS (> 0.9 wt%) noticeably caused larger droplet sizes, thereby diminishing the printability of MP-based HIPEs. These findings provide a promising strategy for developing high-performance and consumer-satisfaction 3D printing inks using MP-stabilized HIPEs.

Effect of NaCl concentration on the formation of high internal phase emulsion based on whey protein isolate microgel particles

At present, the effect of structural modification of microgel particles on high internal phase emulsions (HIPEs) is less studied. In this study, the structural modification effect of NaCl on whey protein isolate microgels (WPIMPs) was comprehensively characterized and applied to the construction of HIPEs. WPIMPs were prepared with NaCl (0–150 mM) and the structural changes were analyzed by measuring the particle size, Zeta-potential, and endogenous fluorescence spectra. The results showed that inducing WPIMPs by NaCl enhanced the surface hydrophobicity, decreased the Zeta potential, and elevated the degree of cross-linking. The interfacial behavior of WPIMPs was characterized by measuring interfacial tensions and adsorbed layer properties. The results showed that NaCl induction decreased the interfacial tension, increased the thickness of the adsorbed layer, and improved the viscoelasticity. The HIPEs were analyzed for micromorphology and particle sizes. The results indicated that NaCl-induced WPIMPs favored the formation of HIPEs with small particle sizes and provided HIPEs with superior environmental stability. This study provides a new idea for the structural modification of microgels and a new theoretical basis for the construction conditions of HIPE.

Rheological and tribological properties of high internal phase emulsions stabilized by pH-induced soy protein isolate-carrageenan complex coacervates

Coacervates of protein-polysaccharide complexes that self-assemble through electrostatic interactions exhibit varying morphologies and functional properties. This study investigated the pH range of soy protein isolate (SPI) and κ-carrageenan (κCG) to form complex coacervates in different states and their ability to stabilize high internal phase emulsions (HIPEs). With the increase of pH (from 4.0 to 5.5), electrostatic interaction between SPI and κCG weakened, the yield of SPI/κCG complex coacervates in the system as well as the degree of agglomeration of microstructure gradually decreased. However, in terms of HIPEs, pH5.0 and pH5.5 (especially pH5.5) complex coacervates exhibited better HIPEs formation ability. Excessively complex coacervates could seriously reduce the adsorption rearrangement rate and intermolecular crosslinking behavior of protein molecules at the interface, so the pH5.5 sample with the lowest coacervates yield showed smaller droplet size and higher elastic modulus. The pH5.0 sample exhibited higher initial viscosity in rheological tests, better deformation resistance in large amplitude oscillatory shear (LAOS) tests and better oral friction properties, due to higher complexation degree of coacervates. These findings give improved understandings of structure of pH-induced SPI-κCG complex coacervates in relation to their ability to stabilize HIPEs, which can guide for design of food emulsions.

Key role of three-dimensional reticular interface membranes in the formation of single polysaccharide–stabilized high internal phase emulsions

Although the interfacial activity of polysaccharides is believed to be insufficient for their applications as individual emulsifying stabilizers, four single polysaccharides examined herein, namely sodium carboxymethyl cellulose (Na-CMC), sodium alginate (SA), high-methoxyl pectin (HMP), and low-methoxyl pectin (LMP) are shown to effectively stabilize high internal phase emulsions (HIPEs) at loadings as low as 0.1 wt% under acidic conditions, that is, at pH 0.5–5.2 (Na-CMC), 0.5–4.0 (SA), 1.0–4.2 (HMP), and 1.0–3.0 (LMP). Despite their structural differences, the four studied polysaccharides feature similar HIPE stabilization mechanisms that mainly involve the formation of three-dimensional reticular interface membrane structures with fiber branching chains. Within the pH range suitable for HIPE formation, the polysaccharides mainly exist as nanofiber network structures with a grid width of 50–100 nm but adopt flake-like and other structures at higher pH. Further insights are provided by the relationship between network membrane structures formed at the interface and the fiber network structures formed by polysaccharides in the original aqueous phase. In addition, the inferred emulsification and stabilization mechanisms are shown to be significantly different from those observed for mainstream Pickering HIPE stabilizers. Thus, our work expands the understanding of the interfacial activity function of polysaccharides, provides conceptual thinking reference and design rules for the development of simple, efficient, safe, and cheap polysaccharide-based HIPEs, and supplements and furthers the theory of HIPE stabilization.

In situ growth of the ZIF‐8 on the polymer monolith via CO2‐in‐water HIPEs stabilized using metal oxide nanoparticles and its photocatalytic activity

AbstractHere, the ZnO/polyacrylamide (ZnO/PAM) macroporous composite monolith was first prepared through the radical polymerization of acrylamide in ZnO‐costabilized CO2‐in‐water Pickering high internal phase emulsions (HIPEs). An efficient and green synthesis method was used to prepare the ZnO/PAM porous precursor materials, and ZnO nanoparticles (NPs) were used as a metal ion source to grow the metal organic frameworks (MOF) phase through secondary recrystallization, thereby synthesizing the target MOF/PAM porous monolith. The effects of the contents of ZnO NPs on the formation of HIPEs and properties of the target MOF/PAM composites for the photocatalytic degradation of cationic dye were studied. As the content of ZnO NPs increased to 3.75 wt%, the composite monolith had high mechanical stress (0.24 MPa) at 80% strain and recovered their shape. The as‐synthesized ZIF‐8/PAM composites were characterized using X‐ray diffraction, scanning electron microscope (SEM), Brunauer Emmett Teller (BET), energy dispersive X‐ray spectrometer (EDS) mapping, and TG methods. SEM images showed that the hybrid materials were interconnected, and the sizes of the open macropore and interconnected pore throats were 30–125 and about 2–20 μm, respectively. In addition, the ZIF‐8/PAM material could be used as a high‐efficiency photocatalyst to remove the cationic dye at a fast rate (88.6%).

Fabrication of food-grade Pickering high internal phase emulsions stabilized by the mixture of β-cyclodextrin and sugar beet pectin

Food-grade Pickering high internal phase emulsions (HIPEs) stabilized by a mixture of β-cyclodextrin (β-CD) and sugar beet pectin (SBP) were fabricated for the first time. The factors affecting the microstructures, mechanical properties, and stabilities of the Pickering HIPEs were systematically investigated. The corresponding hybrid particles were also separated and characterized to reveal the formation mechanism. The results indicated that the mixture could induce the formation of HIPEs with an oil phase volume fraction (φ) of 75% using a one-step high-speed shearing process at room temperature. The composition (the mass ratio of β-CD to SBP, Rc/s) and concentration (W) of the mixture had significant effects on the formation and properties of HIPEs. When W ≥ 1.0% and Rc/s = 2:2 or 3:1, HIPEs had smaller oil droplets, higher gel strengths, better centrifugation stabilities and lutein protection effects. The spectral analysis suggested that SBP could adhere to the surface of β-CD particles to form hybrid particles during the homogenization. Compared with native β-CD particles, these hybrid particles had higher ζ-potential absolute values, and the SBP could also increase the viscosity of the aqueous phase, which contributed to the formation and properties of these HIPEs.

W/O high internal phase emulsions (HIPEs) stabilized by a piperazinyl based emulsifier.

In this study, a piperazinyl-based emulsifier (EA/AMPA) was synthesized to prepare water-in-oil (W/O) high internal phase emulsions (HIPEs). Using kerosene as the oil phase, stable HIPEs with internal phase fractions of up to 98% were prepared. This enabled the EA/AMPA to have a high efficiency, as the HIPEs with a 90% internal phase fraction could be easily prepared with 0.1% of EA/AMPA. In addition, the formation of HIPEs was not affected by the addition of Na+. Because of the fact that EA/AMPA has a hydrophilic head with two tertiary amines, EA/AMPA could be easily recovered from the oil phase by adjusting the pH to acidic values. Moreover, the unique structure promoted the formation of stable HIPEs, even with crude oil used as the oil phase. The results indicate that EA/AMPA has the potential to significantly contribute to the preparation of W/O HIPEs and that the design of the hydrophilic head with two tertiary amines can provide a reference for the fabrication of new W/O emulsifiers.

Thermoresponsive starch-based particle-stabilized Pickering high internal phase emulsions as nutraceutical containers for controlled release

Pickering high internal phase emulsions (HIPEs) stabilized solely by bioderived starch-based particles hold potential for application in the food and pharmaceutical fields. This paper reports the use of a thermoresponsive 2-hydroxy-3-butoxypropyl starch (HBPS) particle as a representative natural biocompatible material for use as an effective stabilizer for HIPE formation. HBPS is synthesized by using butyl glycidyl ether as a hydrophobic reagent to change the hydrophobic–hydrophilic balance of starch, and then starch-based particles are fabricated by a simple nanoprecipitation procedure. The size of particles increased with an increase in temperature, and the particles are essentially monodisperse with a PDI of about 0.1 when the temperature was above 15 °C. These HBPS particles were subsequently used as an effective stabilizer to fabricate stable oil-in-water (o/w) Pickering HIPEs with an internal phase volume of 80% at different stabilizer concentrations. The results demonstrated that increasing the particle concentration is conducive to the formation of stable Pickering HIPEs with greater stiffnesses. In addition, the nutraceutical material (β-carotene) was encapsulated into HIPEs and in vitro release experiments revealed that the release in this system can be controlled by adjusting the temperature.

Ultrasound pre-fractured casein and in-situ formation of high internal phase emulsions.

Traditional preparation of protein particles is usually complex and tedious, which is a major issue in the development of Pickering high internal phase emulsions (HIPEs). In this study, a facile and in-situ method for the preparation of food-grade Pickering HIPEs was developed using ultrasound pre-fractured casein flocs. The ultrasonic-treated casein protein and resulting Pickering HIPEs were characterised using particle size distribution, confocal laser scanning microscopy (CLSM), cryo-SEM, and rheological measurement. The results indicated that pH values of casein and ultrasonic power level were key parameters for casein protein dispersion into nanoparticles to form o/w Pickering HIPEs. In optimal conditions, the hexagons of emulsion droplets were close together, and the emulsions formed with ultrasonic caseins exhibited gel-like behaviour. Additionally, ultrasonic microscale-sized caseins (about 25μm) disappeared upon the use of high speed homogenisation during the formation of HIPEs, while the chemical distribution revealed by confocal laser scanning microscopy indicated that the dispersive nanoparticles from casein proteins were evidently absorbed on the interface of HIPEs (cryo-SEM). These findings prove that ultrasound is an effective tool to loosen casein flocs to induce the in-situ formation of stabilised Pickering HIPEs. Overall, this work provides a green and facile route to convert edible oil into a soft solid, which has great potential for applications in biomedical materials, 3D printing technology, and various cosmetics.

High loading contents, distribution and stability of β-carotene encapsulated in high internal phase emulsions

High internal phase emulsions (HIPEs), stabilized with genipin crosslinked chitosan (CS) microgels, were found to significantly increase the loading contents of β-carotene, up to 2 wt% with only 0.1 wt% microgel as the emulsifiers. With much smaller amount of emulsifiers less than one-tenth, the loading content of β-carotene in the emulsion system was significantly increased by more than 10 times compared with those reported in literature. CS microgels could well absorb on the oil-water interface and thus effectively reduced the water/oil contact, which turned out to effectively stabilize the crowed oil phases (in polygonal shape) against mechanical perturbation. CS with high molecular weight was inclined to facilitate the formation of HIPEs. With increased loading amount of β-carotene from 0 to 2 wt%, the HIPEs changed from light blue to yellow green, and further to deep red. Meanwhile, the gel strength decreased, making it liquid-like more, which could be feasible for their application in food systems. Laser confocal microscopy results showed that more β-carotene appeared on the surface of the oil droplets in HIPE system with the elevation of β-carotene loading contents. In addition, with the elevation of β-carotene loading contents, increased amount of β-carotene distributed in the creaming layer and the proportion of β-carotene in oil layer decreased after centrifugation of the HIPE samples. Furthermore, β-carotene encapsulated in the HIPE systems could resist ultraviolet irradiation, thermal treatment, as well as iron ions and hydrogen peroxide in aqueous phase, which could be related to the protection effect from the interfacial CS microgel membrane as well as the crowed oil droplets environment. The stability of the HIPEs formula was also enhanced with the elevation of β-carotene loading contents.

PDMS polymerized high internal phase emulsions (polyHIPEs) with closed-cell, aqueous-filled microcavities.

Emulsion templates can produce a wide range of unique microstructures via solidification of the continuous phase. Some of these structures result in unique, fluid-filled composites reminiscent of biological tissue when the templating droplets develop into closed-cell structures. However, the state-of-the-art falls short in replicating the mechanical and functional response of biological structures due to stiff, fragile, and bio-incompatible materials while lacking systematic processing parameters. This article describes the synthesis of high internal phase, closed-cell, polydimethylsiloxane (PDMS) elastomeric foams which simultaneously achieve biocompatibility, mechanical robustness, flexibility, and selective permeability. Water-in-oil high internal phase emulsions (HIPEs) stabilized by silica nano-particles (SNPs) provide the microstructural template, resulting in a >74% by volume aqueous phase (up to 82%). To overcome the prohibitive barrier to HIPE formation when using a mechanically-superior, but highly viscous commercial PDMS kit, we produce HIPE templates via centrifugation of low internal phase emulsions (LIPEs, <30% by volume dispersed phase). This oil phase crosslinks into an aqueous-filled (water + glycerol + NaCl) elastomeric composite. The composite's microstructural dependence on viscosity ratio, mixing speed, emulsifier concentration, and centrifugal force are systematically characterized. The resulting microstructured, fluid-filled elastomer composites exhibit mechanically robust and highly flexible behavior due to the excellent properties of the PDMS continuous phase.

Synthesis of star polymeric ionic liquids and use as the stabilizers for high internal phase emulsions

A series of well-defined core cross-linked star (CCS) polymeric ionic liquids (PILs) were synthesized via a three-step approach. First, the styrenic imidazole-based CCS polymer (S-PVBnIm) was prepared by the RAFT-mediated heterogeneous polymerization in a water/ethanol solution, followed by the quaternization of S-PVBnIm with bromoalkanes and anion exchange. The CCS polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). The obtained CCS polymers were used as the effective emulsifiers for oil-in-water high internal phase emulsions (HIPEs). Multiple oils with different polarity including n-dodecane, undecanol, toluene and octanol were emulsified using 0.5 wt% S-PVBnIm aqueous solution under the acidic condition to form HIPEs with long-term stabilities. The excellent emulsification properties of CCS PILs were demonstrated by HIPE formation for a variety of oils. The properties of HIPEs in terms of emulsion type and oil droplet size were characterized by the confocal laser scanning microscopy (CLSM). The intriguing capability of CCS PILs to stabilize HIPEs of various oils holds great potentials for the practical applications.

High internal ionic liquid phase emulsion stabilized by metal-organic frameworks.

The emulsification of metal-organic frameworks (MOFs) for the two immiscible phases of water and ionic liquid (IL) was investigated for the first time. It was found that Ni-BDC (BDC = 1,4-dicarboxybenzene) can emulsify water and ILs and favor the formation of high internal phase emulsions (HIPEs) under certain experimental conditions. The microstructures of the HIPEs were characterized by confocal laser scanning microscopy using a fluorescent dye Rhodamine B, which proves that the HIPEs are the IL-in-water type. Further results reveal that the HIPE forms during the IL-in-water to water-in-IL emulsion inversion. The possibilities of the HIPE formation by other MOFs (Cu-BDC and Zn-BDC) were explored and the mechanism for HIPE formation was discussed. The MOF-stabilized HIPE was applied to the in situ synthesis of a MOF/polymer composite by HIPE polymerization. The macroporous MOF/polyacrylamide network and MOF/polystyrene microspheres were obtained from the HIPEs, respectively.

Synergistic stabilization and tunable structures of Pickering high internal phase emulsions by nanoparticles and surfactants

The preparation of Pickering emulsions with an internal phase volume fraction of exceeding 95% is still a challenge to date. In this work, Pickering high internal phase emulsions (HIPEs) with an ultrahigh internal phase fraction of 98.5% were prepared using hydrophobic silica nanoparticles (H30) and nonionic surfactant of Span 85 as a dual emulsifier system. Water-in-hexane (W/O) HIPEs stabilized by a mixture of H30 and Span 85 were investigated. Increasing Span 85 concentration in mixture would result in the appearance of smaller droplets of several to tens of micrometers in the HIPEs while a population of large droplets of hundreds of micrometers would appear with increasing H30 concentration. Furthermore, the influences of Span 85 and H30 on the formation of HIPEs were investigated from the polymerized HIPEs (polyHIPEs) synthesized through these HIPEs templates using styrene as the oil phase. The synergism between particles and surfactant exists and plays a crucial role in the stability of HIPEs. This research opens up a new insight into the fabrication of Pickering HIPEs with an ultrahigh internal phase fraction.

Biodegradable Fumarate-Based PolyHIPEs as Tissue Engineering Scaffolds

PolyHIPEs show great promise as tissue engineering scaffolds due to the tremendous control of pore size and interconnectivity afforded by this technique. Highly porous, fully biodegradable scaffolds were prepared by polymerization of the continuous phase of high internal phase emulsions (HIPEs) containing the macromer poly(propylene fumarate) (PPF) and the cross-linker propylene fumarate diacrylate (PFDA). Toluene was used as a diluent to reduce the viscosity of the organic phase to enable HIPE formation. A range of polyHIPE scaffolds of different pore sizes and morphologies were generated by varying the diluent concentration (40-60 wt %), cross-linker concentration (25-75 wt %), and macromer molecular weight ( M n = 800-1000 g/mol). Although some formulations resulted in macroporous monoliths (pore diameter >500 microm), the majority of the polyHIPEs studied were rigid, microporous monoliths with average pore diameters in the range 10-300 microm. Gravimetric analysis confirmed the porosity of the microporous monoliths as 80-89% with most scaffolds above 84%. These studies demonstrate that emulsion templating can be used to generate rigid, biodegradable scaffolds with highly interconnected pores suitable for tissue engineering scaffolds.