Stable High Internal Phase Emulsions Research Articles

Highly Persistent and Robust Emulsion Stabilized by Hierarchical Cellulose Microgel through Stereo-hindrance under Extreme Conditions.

Emulsion stabilization oil-in-water under harsh conditions (e.g., hypersaline, acid and alkali, and high temperature) is a great challenge for conventional emulsion stabilizers, including surfactants or particles. Herein, a persistent and robust emulsion under harsh conditions is achieved via a sustainable solution based on a hierarchical cellulose microgel (h-CMG). h-CMG in aqueous suspension establishes stable 3D networks by its nanotentacles and microbody, which can spatially hinder the approach and coalescence of droplets to each other and stabilize the emulsion. Unlike the emulsion stabilized by minimizing the interfacial energy and protecting the water/oil interface, the emulsion spatially stabilized by h-CMG exhibits extensive tolerance to extreme conditions and the feature of stable high internal phase emulsion (80%, v/v). The related droplet size and emulsion volume are almost unchanged in the pH range of 1 to 14, in NaCl aqueous solution of 2 mol/L, or even at 80 °C for 12 h. This genuine biobased emulsifier is highly favorable to the food, cosmetics, and pharmaceutical industries without the risk of nanotoxicity, and it also can provide a reliable emulsifier for the chemical and drilling industries involving harsh operation circumstances.

Synthesis of PEG-Polycycloether Block Copolymers: Poloxamer Mimics Containing a Rigid Helical Block.

Poloxamers are amphiphilic block copolymers consisting of poly(ethylene glycol) (PEG) and poly(propylene glycol) segments. Their self-assembly and interfacial properties are tied to the relative hydrophilicity and hydrophobicity of each block and can therefore be adjusted by changing block lengths. Here, a series of PEG-polycycloether block copolymers is synthesized that have the same structure as a poloxamer, but they encompass a rigid polycyclic backbone as the hydrophobic block. A variety of polymer structures are synthesized, for example diblock or triblock architectures, with/without olefinic units, atactic or isotactic backbone, and different block lengths. Due to their amphiphilicity, self-assembly into spherical aggregates (diameters ranging from 64 to 132nm) at low concentrations (critical aggregation concentration as low as 0.04mgmL-1) is observed in water. Low surface tensions (as low as 26.7 mNm-1) are observed as well as the formation of stable high internal phase emulsions (HIPEs) irrespective of the oil/water ratio. This contrasts with the properties of the commonly used poloxamers P188 or P407 and illustrates the significance of the rigid polycycloether block. These new colloidal properties offer new prospects for applications in emulsion formulations for biomedicine, cosmetics, and the food industry.

Highly Macroporous Polyimide with Chemical Versatility Prepared from Poly(amic acid) Salt-Stabilized High Internal Phase Emulsion Template.

Macroporous polymers have gained significant attention due to their unique mass transport and size-selective properties. In this study, we focused on Polyimide (PI), a high-performance polymer, as an ideal candidate for macroporous structures. Despite various attempts to create macroporous PI (Macro PI) using emulsion templates, challenges remained, including limited chemical diversity and poor control over pore size and porosity. To address these issues, we systematically investigated the role of poly(amic acid) salt (PAAS) polymers as macrosurfactants and matrices. By designing 12 different PAAS polymers with diverse chemical structures, we achieved stable high internal phase emulsions (HIPEs) with >80 vol % internal volume. The resulting Macro PIs exhibited exceptional porosity (>99 vol %) after thermal imidization. We explored the structure-property relationships of these Macro PIs, emphasizing the importance of controlling pore size distribution. Furthermore, our study demonstrated the utility of these Macro PIs as separators in Li-metal batteries, providing stable charging-discharging cycles. Our findings not only enhance the understanding of emulsion-based macroporous polymers but also pave the way for their applications in advanced energy storage systems and beyond.

Novel concentrated O/W emulsion co-stabilized by like-charged chitosan nanoparticle and ethyl lauroyl arginate (LAE) surfactant at very low dosages

Emulsions co-stabilized by like-charged cationic ethyl lauroyl arginate (LAE) and positively charged chitosan/sodium tripolyphosphate (CS-TPP) nanoparticles at low doses were prepared. The effects of CS-TPP nanoparticle concentration, LAE concentration, and pH on storage stability and mean droplet diameter were investigated, and the emulsion microstructure was examined by confocal laser scanning microscopy. The emulsions formed by LAE and CS-TPP were O/W emulsions, different from W/O emulsions formed by CS-TPP alone. The stability of the emulsions co-stabilized by LAE and CS-TPP was superior to that of the emulsions stabilized by LAE alone or CS-TPP nanoparticles alone. The emulsions could maintain good stability with 0.5 mM LAE and 0.08 wt% CS-TPP at pH ranging from 3.5 to 5.5. After standing and layering, the upper cream layer of CS-TPP+LAE emulsions could form stable high internal phase emulsions. For the novel emulsion, LAE dominated the formation of emulsion droplets, and adsorbed CS-TPP nanoparticles played a crucial role in the emulsion stability. The adsorbed CS-TPP nanoparticles discretely attached to oil droplets could form a strawberry-like construct, which could prevent the coalescence of emulsion droplets through electrostatic repulsion and steric hindrance. This work demonstrates the capacity of low dose food-grade emulsifiers and stabilizers to form stable emulsions.

A tuning molecular conformation strategy of interfacial glycosylated cod proteins enables high internal phase emulsions with freeze-thaw stability

Sugar is known to be used as a protective agent for protein function during lyophilization. However, it has not been reported that sugar changes protein structure during lyophilization process, thus improving protein functional properties. In this study, the freeze-thaw stable high internal phase emulsions (HIPEs) could be prepared by the glycosylated cod protein lyophilized with glucose, but not the glycosylated cod protein which was lyophilized before adding glucose. The results showed that β-turn content of the protein lyophilized with glucose disappeared while β-sheet increased sharply (from 34.0 ± 2.4 to 41.2 ± 1.8) at the sublimation stage in the lyophilization. This might be one of the key factors for preparing freeze-thaw stable HIPEs because it was easier for protein to form stable layers around the oil droplets to against the oil or ice crystals. The obtained results are expected to change the role of lyophilization in the field of protein application, enabling the development of new materials.

High internal phase emulsions stabilized by pea protein isolate-inulin conjugates: Application as edible inks for 3D printing

High internal phase emulsions (HIPEs) are soft materials that can be designed to contain nutrients and active agents. As a result, they are being explored for their potential application as edible inks in 3D food printing applications. However, the rheological characteristics of HIPEs are often unsuitable for this purpose, resulting in unsatisfactory precision and resolution performance during 3D printing. This study aims to overcome these problems by creating HIPEs with improved rheological properties by using pea protein-inulin glycosylation products as plant-based emulsifiers. These conjugates were prepared from pea protein isolate (PPI) and inulin by glycosylation using a combined ultrasound/pH-shift method. The oil phase of these emulsions consists of omega-3 rich algal oil and lemon oil. We showed that stable HIPEs could be formed at an oil phase content of 80%. At this oil content, the oil droplets were uniform and stable, and the emulsions exhibited higher storage modulus. Compared to PPI alone or physical mixture of PPI and inulin, PPI-inulin conjugates formed oil droplets with smaller diameters and better uniformity, as well as thicker and denser biopolymer coatings. Compared with protein alone, the rheological analysis demonstrated that the HIPEs formulated with PPI-inulin conjugates had a higher viscosity, higher elasticity, higher recovery rate, and better thixotropy, indicating that they had physiochemical characteristics suitable for edible inks applications. This was confirmed by using the HIPEs as edible inks to 3D print model food objects. In conclusion, the pea protein-inulin conjugates fabricated in this study can be used as plant-based emulsifiers to form edible inks based on HIPEs. In principle, a range of nutrients and other bioactive agents could be incorporated into these inks for personalized nutrition applications.

Hydrophilic macroporous monoliths with tunable water uptake capacity fabricated by water‐in‐oil high internal phase emulsion templating

AbstractIn this contribution, a series of well‐defined amphiphilic di‐block copolymers poly(ethylene oxide)‐b‐polystyrene (PEO43‐b‐PSx) with different PS segment lengths of x = 41, 78, and 130 units were synthesized through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The as‐prepared block copolymers successfully stabilized the water‐in‐oil (W/O) high internal phase emulsions (HIPEs) containing pH responsive monomers 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and 2‐(diethylamino)ethyl methacrylate (DEAEMA). The effect of macro‐surfactant loading, PS segment length, and DMAEMA/DEAEMA content on the stability of HIPEs and the corresponding polyHIPE structure were investigated. Results show that the average void size of polyHIPE decreases with the increase of surfactant concentration. Macroporous morphologies with closed‐cell or open‐cell can be manipulated by surfactant loading as well. The openness of polyHIPE decreases as the increase in hydrophobic PS segment length. Compared to DMAEMA containing HIPE systems, stable DEAEMA containing HIPEs are more easily obtained by using the as‐prepared macro‐surfactant. Stable HIPE with a relatively large amount of DEAEMA, up to 70 vol% of oil‐phase has been achieved. The obtained PDEAEMA‐co‐PS polyHIPEs derived from 0.116 mol% PEO43‐b‐PS41 stabilized emulsion templates show pH responsiveness towards water absorption and the highest acidic water uptake capacity can be up to 6.6 times its weight at equilibrium state. This work paves the way for the preparation of hydrophilic macroporous monolith from stable W/O HIPE template, and confirms the strength of macro‐surfactant in such an approach.

High Internal Phase Emulsions Preparation Using Citrus By-Products as Stabilizers.

The citrus juice industry produces about 50% of by-products. Citrus pomace (CP) contains many polysaccharides (mainly cellulose and pectin), which could act as stabilizers and emulsifiers. The aim of this work was to obtain high internal phase emulsions (HIPEs) using unmodified CP at different concentrations to valorize citrus by-products. The synergic effect of pea protein isolate (PPI) with CP to stabilize the HIPEs was also studied. HIPEs structure was analyzed using rheological and microscopy studies as well as color and physical stability of the emulsions. According to rheological data, all samples exhibited a solid-like behavior, as elastic modulus (G’) was higher than viscous modulus (G’’) within the viscoelastic linear region; as % CP and % PPI increased, greater values of G’ and apparent viscosity (η) were achieved. Microscopic images showed that oil droplets had a polyhedral shape and were enclosed by a thin layer of CP and PPI. Increasing concentrations of CP and PPI enhanced oil droplets packaging. Emulsions’ physical stability was better when adding PPI. The results showed that stable HIPEs with 1.25% of CP and PPI over 0.5% can be obtained. These HIPEs could be used to formulate emulsions for food applications, such as mayonnaises, fillings, or creams.

Hydrophobically modified chitosan microgels stabilize high internal phase emulsions with high compliance

Food-grade microgel-stabilized emulsions have been attracting much attention due to their promising applications in food formulations. In this study, the use of hydrophobically modified chitosan microgels (h-CSMs) as particle emulsifiers to stabilize high internal phase emulsions (HIPEs) was demonstrated for the first time. Four hydrophobically modified chitosan (h-CS) were obtained by grafting deoxycholic acid (DA) with chitosan (CS) at grafting rates of 4.64%, 13.21%, 15.12% and 30.29%, respectively. The selected modified chitosan were further cross-linked with sodium tripolyphosphate (TPP) to form h-CSMs. It was found that, compared to pure CS and the modified h-CS, the h-CSMs have higher hydrophobicity, and can stabilize oil-in-water HIPEs effectively. The interfacial properties of the h-CSMs, and the formation, microstructure and rheological properties of HIPEs were characterized by dynamic interfacial adsorption, contact angle, visual observation, laser confocal microscopy and rheological measurements, respectively. The results show that stable HIPEs with oil concentration up to 90 wt% can be formed using very low h-CSM particle concentration (only 0.05 wt% for the HIPE with 90 wt% oil), and the HIPEs stabilized by h-CSMs displayed higher rheological compliance than other solid particle stabilized HIPEs at high oil volume fraction. The strong emulsification properties of the h-CSMs are attributed to their increased hydrophobicity, the enhanced exposure of hydrophobic groups during microgelation process, and the viscoelasticity of h-CSMs.

High internal phase emulsions stabilized solely by sonicated quinoa protein isolate at various pH values and concentrations

In this study, stable high internal phase emulsions (HIPEs) constructed solely by sonicated quinoa protein isolate (QPI) at various pH values and protein concentrations (c) were constructed, and differences of HIPE microstructures at these conditions were discussed. HIPEs stabilized by QPI at pH 7.0, 9.0 possessed smaller droplet size (14–24 μm), smoother appearance, and higher physical stability which were caused by polyhedral framework microstructure. However, at acidic conditions, QPI aggregates filled in the gaps between droplets (30–52 μm) instead of adsorbing to oil–water interface, which decreased the stability. The solid-like viscoelasticity of HIPEs were enhanced when the c increased while the increment of pH value had the significant opposite effect (decreased from about G′ 1000 Pa, G″ 280 Pa to G′ 350 Pa, G″ 50 Pa) due to the microstructure difference. This study broadens the commercial applications of quinoa protein in novel food products like fat substitutes.

Desalted duck egg white nanogels combined with κ‐carrageenan as stabilisers for food‐grade Pickering emulsion

SummaryThere was an extensive interest in food‐grade Pickering emulsions formulated by natural stabilisers owing to the gradual growing demand for pursuing green‐label products. Based on this, the desalted duck egg white nanogels (DEWN) combined with κ‐carrageenan (CAR) (CAR/DEWN) were used as stabilisers to prepare environment‐friendly Pickering emulsions. The DEWN and CAR/DEWN as well as the particles‐stabilised emulsions were all characterised. Compared with the DEWN‐ and CAR‐stabilised emulsions, Pickering emulsions based on CAR/DEWN were investigated to illustrate the long‐term stability according to the results of visual appearance, static multiple light scattering and centrifugation experiments. In addition, CAR/DEWN could prepare stable high internal phase emulsions, which may give a new perspective for nutraceutical or drug encapsulation and delivery. Adding CAR to the DEWN not only increased the apparent viscosity of the emulsions to 122.2% but also enhanced the thixotropic recovery rate to 87.7%. In general, CAR/DEWN as stabilisers significantly promoted the Pickering emulsions' properties, and provided a possibility for the application of Pickering emulsion in foods.

W/O high internal phase emulsion featuring by interfacial crystallization of diacylglycerol and different internal compositions

High internal phase emulsions (HIPEs) show promising application in food and cosmetic industries. In this work, diacylglycerol (DAG) was applied to fabricate water-in-oil (W/O) HIPEs. DAG-based emulsion can hold 60% water and the emulsion rigidity increased with water content, indicating the water droplets acted as “active fillers”. Stable HIPE with 80% water fraction was formed through the combination of 6 wt% DAG with 1 wt% polyglycerol polyricinoleate (PGPR). The addition of 1 w% kappa (κ)-carrageenan and 0.5 M NaCl greatly reduced the droplet size and enhanced emulsion rigidity, and the interfacial tension of the internal phase was reduced. Benefiting from the Pickering crystals-stabilized interface by DAG as revealed by the microscopy and enhanced elastic modulus of emulsions with the gelation agents, the HIPEs demonstrated good retaining ability for anthocyanin and β-carotene. This study provides insights for the development of W/O HIPEs to fabricate low-calories margarines, spread or cosmetic creams.

Effect of pH and Pea Protein: Xanthan Gum Ratio on Emulsions with High Oil Content and High Internal Phase Emulsion Formation.

Electrostatic interaction between protein and polysaccharides could influence structured liquid oil stability when emulsification is used for this purpose. The objective of this work was to structure sunflower oil forming emulsions and High Internal Phase Emulsions (HIPEs) using pea protein (PP) and xanthan gum (XG) as a stabilizer, promoting or not their electrostatic attraction. The 60/40 oil-in-water emulsions were made varying the pH (3, 5, and 7) and PP:XG ratio (4:1, 8:1, and 12:1). To form HIPEs, samples were oven-dried and homogenized. The higher the pH, the smaller the droplet size (Emulsions: 15.60–43.96 µm and HIPEs: 8.74–20.38 µm) and the oil release after 9 weeks of storage at 5 °C and 25 °C (oil loss < 8%). All systems had weak gel-like behavior, however, the values of viscoelastic properties (G′ and G″) increased with the increment of PP:XG ratio. Stable emulsions were obtained at pHs 5 and 7 in all PP:XG ratios, and at pH 3 in the ratio 4:1. Stable HIPEs were obtained at pH 7 in the ratios PP:XG 4:1, 8:1, and 12:1, and at pH 5 at PP:XG ratio 4:1. All these systems presented different characteristics that could be exploited for their application as fat substitutes.

Development of rheologically stable high internal phase emulsions by gelatin/chitooligosaccharide mixtures and food application

Gelatin (GE) modified by chitooligosaccharide (COS) through electrostatic interaction and hydrogen bond was applied to stabilize food-grade high internal phase emulsions (HIPEs) via a facile way. The influence of COS on rheological stability and practical food application of HIPEs was investigated. The interaction between GE and COS promoted a tighter connection between GE and COS, endowed the interfacial membrane with strong structure to anti-deformation, and prevented the accumulation of emulsion droplets by steric hindrance effect. Rheological analysis further proved that COS could lead to high viscosity, high elasticity, excellent oscillation performance, high recovery rate, great thixotropy and the strengthened structure of HIPEs, suggesting the outstanding rheological stability for three dimensional (3D) printing. Subsequent 3D printing on colored card and food confirmed that the obtained HIPE had good extrudability and printing performance. This study could provide important implications for the development of food-grade rheologically stable HIPE and promote the potential food application in rapid prototyping.

Preparation and characteristics of high internal phase emulsions stabilized by rapeseed protein isolate

Rapeseed protein isolate (RPI) was used as a natural particulate emulsifier for production of high internal phase emulsions (HIPEs) for the first time. RPI was prepared by an alkali solution and acid precipitation process, following mixed with rapeseed oil (oil phase) to form HIPEs using a combination of low-speed stirring and high-speed homogenization. The best condition of homogeneous and stable HIPEs that formed by RPI was at a pH = 9.0 and a protein concentration of 20 g/L. Under this condition, the proteins adsorbed around the oil phase to form a stable network structure. Stable HIPEs could have a maximum oil content of up to 840 g/kg (oil phase/emulsion), and the appearance and microstructure of which containing above 300 mmol/L NaCl did not change significantly (p = 0.08) after three freeze-thaw cycles. Overall, the HIPEs stabilized by RPI exhibited an excellent oil loading capacity and freeze-thaw stability, which not only utilizes the low value protein resources in the waste rapeseed meal, but also provides a theoretical basis for the application of HIPEs in food industry.

Single-Step Fabrication of a Multiscale Porous Catalyst Layer by the Emulsion Template Method for Low Pt-Loaded Proton Exchange Membrane Fuel Cells

Multiscale porosity assures better mass transport for a low Pt-loaded fuel cell; however, achieving a complex pore structure in a simple manner presents a major challenge. In this work, by using the emulsion template method, a multiscale porous catalyst layer with macro- and mesopores was fabricated in a single step. A stable high internal phase emulsion is achieved with catalyst layer components by exploiting a Nafion ionomer as a surfactant. The oil phase of the emulsion catalyst slurry induces the macropores, and the Pt/C and ionomer mixture in the hydrophilic solvent forms a mesoporous framework in the catalyst layer. Scanning electron microscopy and micro X-ray computed tomography confirmed the formation of uniform and well-interconnected macropores. The performance of the low Pt-loaded catalyst layer derived from the emulsion template method considerably improved the mass transport property due to the mitigation of water flooding. The fabrication of an emulsion-based catalyst layer provides an efficient platform to design high-performance low Pt-loaded fuel cells.

High internal phase emulsions solely stabilized by natural oil-based nonionic surfactants as tea tree oil transporter

The stable high internal phase emulsions (HIPEs) were solely stabilized by Palm kernel oil ethoxylates (SOE-N-60) and used as the delivery system of tea tree oil (TTO). The effects of internal phase volume fraction, SOE-N-60 concentration and emulsification time on the stability of HIPEs were studied systematically by Mastersizer 2000 instrument, Lx POL polarizing microscope and rheometer, etc. The experimental results demonstrated that stable HIPEs with internal phase fraction of 84 vol% can be only prepared with 5 wt% surfactant concentrations. Microscopy images showed that the deformation of emulsion droplet and the particle size distribution of the HIPEs were polydispersity. Rheological tests also proved that the emulsion exhibited elastic-gel properties and deformation recovery degree could reach 90 %. The antibacterial experiment indicated that HIPEs prepared by natural oil-based surfactant can effectively protect the encapsulated tea tree oil (TTO), which not only increased the bioavailability of tea tree oil, but also effectively solved the disadvantages of TTO such as volatile and hydrophobic. In addition, the HIPEs stabilized by SOE-N-60 had excellent stability, which will broaden its potential applications in medicine, food and personal care.

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.

High-internal-phase emulsions (HIPEs) for co-encapsulation of probiotics and curcumin: enhanced survivability and controlled release.

Synergistic biological activities of probiotics and curcumin can be achieved based on the gut-brain axis. However, it is still a challenge for utilizing both of them in actual food products due to their high sensitivity to environmental conditions. In the present study, high-internal-phase emulsions (HIPEs) were fabricated to co-encapsulate the probiotics and curcumin in response to the customer demand for convenience. β-Lactoglobulin-propylene glycol alginate composite hydrogel particles (β-lgPPs) with proper size and intermediate wettability were prepared at β-lg to PGA mass ratio of 2 : 1 and employed as particulate emulsifiers. Stable HIPEs with a fixed oil fraction (φ = 0.8) could be formed within a wide range of β-lgPPs concentrations, ranging from 0.1 to 2.0 wt%. Confocal laser scanning microscopy (CLSM) images indicated that the interfacial structure of the oil droplets was composed of both β-lg nanoparticles and a PGA network, which jointly contributed to the gel-like structures in HIPEs. An increase in elasticity and gel strength, as well as centrifugal stability, could be achieved by elevating the particle concentration as determined by diffusing wave spectroscopy and Lumisizer analysis. HIPEs with high particle concentrations showed a high resistance against pasteurization since no obvious flocculation or coalescence could be observed in these emulsions. HIPEs also provoked a significant reduction in the death of LGG as well as the chemical degradation of curcumin: up to 7.91 log CFU cm-3 of LGG and 93.0% of curcumin were retained after pasteurization treatment. Moreover, the HIPEs could also retard the release of curcumin and protect the LGG in simulated gastrointestinal tract conditions. The results from this work provide useful information for developing a promising delivery system for the co-encapsulation of curcumin and probiotics.

Sonochemical effects on formation and emulsifying properties of zein-gum Arabic complexes

Zein is a widely used plant protein, but its application is limited by its poor water solubility under neutral conditions. In this work, we present an approach to develop a water-soluble zein-gum arabic (GA) complex and to explore its application in stabilizing lemon oil-in-water emulsions. As a simple, inexpensive and rapid method, sonication was used to accelerate the glycation reaction between zein and GA. The grafting degree of zein and GA was highest when the sonication power was 400 W and the treatment time was 25 min. SDS-PAGE and 1H NMR confirmed the formation of covalent bonds between zein and GA. The water-dispersibility, antioxidant activity, and thermal stability of zein-GA conjugates were better than those of native zein. The conjugates were used to form stable high internal phase emulsions (HIPEs) containing 80% v/v oil, which had relatively small mean droplet diameter (<10 μm). The HIPEs were semi-solids that exhibited strong shear-thinning behavior. After encapsulation in the HIPEs, the chemical degradation of lemon oil when exposed to UV-light and heat was significantly reduced. This study shows that the functional performance of zein can be extended by covalently linking it to GA using a combination of sonication and heat.