Recent progress in emulsion gels: from fundamentals to applications

Double cross-linked emulsion gels stabilized by flaxseed protein and chitosan: Effects of CaCO3 content on gel properties, stability and curcumin digestive characteristics

In Ca2+-induced emulsion gels, rapid Ca2+ release leads to uneven gel structures, impairing curcumin (Cur) protection and delivery. To overcome this issue, a novel approach combining low-temperature heating (40 °C) and mild acidic environments (pH 6.5) was proposed to gradually releas Ca2+ from CaCO3. This strategy significantly improves the mechanical properties and stability of flaxseed protein (FP)-chitosan (CS) emulsion gels by forming a uniform and dense network structure. At a CaCO3 concentration of 15 mg/mL, the gel exhibited optimal performance, increasing Cur's photostability and storage stability by 44.0 %, 41.1 %, and 23.3 %, respectively, compared to the control (Cur-oil). Increasing the CaCO3 concentration also inhibited the release of Cur and free fatty acids, reducing bioaccessibility during in vitro digestion. Overall, this study provides new insights into the stability of bioactive compounds and expands the application of CaCO3-induced emulsion gels as delivery systems in the food industry.

Soy protein isolate‑sodium alginate emulsion gel co-construction of a dual network system for the development of three-dimensional simulated fats: Effect of sodium alginate concentration and calcium ion addition

This study developed a solid emulsion gel by focusing on internal gel network formation using soy protein isolate, sodium alginate (SA), perilla oil, gluconolactone (GDL), and calcium carbonate, assessed its potential as a fat substitute. Hypotheses on the process and mechanism of gel formation were developed by analyzing the effects of different concentrations of SA and Ca2+ on the gelation properties. Results indicated appropriate SA and Ca2+ concentrations facilitated complex interpenetrating dual-network structures in the GDL environment. Rheological and oral friction measurements demonstrated that elevated SA and Ca2+ levels enhanced gel formation and improved its juicy properties. However, excessive concentrations (1.2 wt% SA) reduced the gel properties and resulted in inhomogeneous networks. These results of dual-network (DN) solid gels offer a strategy for creating edible simulants and provide a theoretical basis for more comprehensively exploring the gel properties of food.

Hemp seed oil-based emulsion gels stabilized by soybean protein isolate, inulin, and glyceryl monostearate: Phase inversion and baking application

This study delved into the potential of hemp seed oil (HSO)-based emulsion gels stabilized by soybean isolate protein (SPI) using high-speed dispersion method as innovative butter substitutes in the bakery industry, offering a dual benefit of health and functionality. In order to better mimic the properties of butter, the storage stability and plasticity of the emulsion gel were increased by successive attempts to add inulin to the SPI solution and glycerol monostearate (GMS) to the hemp seed oil as structuring agents. There was phase inversion as GMS added, 2 % GMS addition caused phase inverted from O/W to semibicontinuous, and W/O appeared when GMS increased to 4 % or more. This was because that GMS crystals could bind neighboring droplets, reduced the spatial resistance provided by the SPI, collapsed the original oil-in-water structure. This novel emulsion was integrated as a novel fat replacer in cakes, and 25 % replacement cakes was regarded as optimal substitution of commercial butter through texture profile analysis and sensory assessment. This research advances the potential use of HSO emulsion gels as substitutes for fats in baking applications.

Recent Advances in Plant-Based Edible Emulsion Gels for 3D-Printed Foods

3D printing has emerged as a suitable technology for creating foodstuff with functional, sensorial, and nutritional attributes. There is growing interest in creating plant-based foods as alternatives to address current demands, especially to tailor consumer preferences. Consequently, plant-derived edible inks for additive manufacturing have emerged as suitable options, including emulsion gels (or emulgels). These gels can be formulated entirely from plant-derived lipids, proteins, polysaccharides, and/or other ingredients to form complex fluids that belong to the category of soft matter. This review summarizes the most recent advances in the areas of formation, structuring, properties, and applications of plant-based emulsion gels for 3D-printed food. These semisolid materials can be extruded to the set or solidified into structures with predesigned shapes, fidelity, and sensory attributes across the senses (taste, smell, sight, and touch) along with nutrition values. Emulsion gels can be formed by either solely gelling the continuous phase or combining this process with the formation of a particle network through aggregation and close packing. The current challenges facing the development of edible inks using plant-based materials are critically discussed to stimulate further advances in the rapidly growing field of personalized 3D-printed foods.

Synergistic stabilization of oil-in-water emulsion gels by pea protein isolate and cellulose nanocrystals: Effects of pH and application to 3D printing

In this study, pea protein isolate (PPI) and cellulose nanocrystals (CNC) were used to prepare oil-in-water emulsions, and the effects of pH and the oil content on the properties of the emulsions were investigated. The microstructural analysis revealed that PPI and CNC formed complexes by electrostatic attraction at pH 3.0 and 4.5, which assembled a dense interfacial layer around the oil droplets, improving emulsification performance. Moreover, the emulsions at these pH conditions exhibited semi-solid gel properties when the oil content was increased to 75 wt%, with better viscoelasticity compared to pH 8.0 and high thixotropic recovery rates in rheological experiments. Printing of flat stacked models with these high internal phase emulsions had a deformation rate of around 5 %, indicating desirable shear resistance and fidelity. These findings would offer valuable insights for developing fat substitutes and their application as edible inks for 3D printing.

Whey Protein Hydrogels and Emulsion Gels with Anthocyanins and/or Goji Oil: Formation, Characterization and In Vitro Digestion Behavior

Whey protein isolate (WPI) has functional properties such as gelation and emulsification. Emulsion gels combine the benefits of both emulsions and hydrogels. In this study, WPI hydrogels and emulsion gels were developed with goji oil (GO) as the oil phase by the inclusion of blueberry extract (BE) in the protein matrix. Heat-denatured WPI (hWPI) particles and emulsions were characterized in terms of size distribution, ζ-potential, interfacial protein, and anthocyanin partition. The inclusion of anthocyanins-rich blueberry extract led to the aggregation of hWPI particles, but it also increased the interfacial protein of 10% goji oil emulsions to 20% and decreased their size distribution to 120 and 325 nm. WPI hydrogels and emulsion gels were analyzed in terms of their water-holding capacity, which decreased from 98% to 82% with the addition of blueberry extract and goji oil. Syneresis, rheological, and morphological characteristics were also analyzed. The gelation time of hWPI particles and emulsions was shortened from 24 h to 12 h when incorporating blueberry extract to form a dense network. The network was the most homogeneous and densest in the presence of 3% blueberry extract and 5% goji oil. The co-inclusion of blueberry extract and goji oil increased the syneresis during the freeze-thaw cycles, with the values rising from 13% to 36% for 5% BE hydrogel and BE-containing emulsion gels after the first cycle. All WPI hydrogels and emulsion gels exhibit predominantly elastic behavior. Moreover, anthocyanin release, antioxidant activity, and the fatty acid composition profile were also analyzed during in vitro digestion. Soluble and free anthocyanins in the digested medium were reduced with the goji oil content but increased with the blueberry extract content. The stability of polyunsaturated fatty acids in the digested medium was improved by the addition of blueberry extract. The antioxidant activity of the digested medium increased with the content of blueberry extract but decreased with the content of goji oil. The ABTS∙+ scavenging capacities decreased from 63% to 49% by increasing the content of GO from 0% to 10% and they increased from 48% to 57% for 5% BE and 10% GO emulsion gels as the BE content increased from 0% to 5% after 6 h of digestion. The data gathered should provide valuable insights for future efforts to co-encapsulate hydrophilic and hydrophobic agents, thereby enhancing their stability, bioavailability, and functional properties for potential applications in food industries.

Jammed Pickering Emulsion Gels

Emulsion gels with specific rheological properties have widespread applications in foods, cosmetics, and biomedicines. However, the constructions of water-in-oil emulsion gels are still challenging, due to the limited interactions available in the continuous oil phase. Here, a versatile strategy is developed to prepare a new type of emulsion gels, called Jammed Pickering emulsion gels (JPEGs). In the JPEG system, SiO2 NPs in the oil phase serve as colloidal surfactants to stabilize water-in-oil Pickering emulsions, while positively-charged NH2-PEG-NH2 molecules in the water phase cross-link negatively-charged SiO2 NPs at the water/oil interface, making NP-stabilized water droplets hard to deform and thus jamming the emulsion system to form emulsion gels. The strategy to prepare JPEGs is versatile and applicable to diverse oil phases. The designed JPEGs possess many advantages, including good biocompatibility for widespread applications, shear-thinning rheological properties for easy processing, good stability Over a wide temperature range and Against centrifugation, good adhesion to wet tissues for tissue engineering, and well-controlled sustained release Under intestinal conditions. The developed JPEGs are demonstrated to be a promising delivery platform and the strategy to achieve JPEGs will trigger more innovations of material design.

Seven sour substances enhancing characteristics and stability of whey protein isolate emulsion and its heat-induced emulsion gel under the non-acid condition

Protein emulsion gels, as potential novel application ingredients in the food industry, are very unstable in their formation. However, the incorporation of sour substances (phosphoric acid, lactic acid, acetic acid, malic acid, glutamic acid, tartaric acid and citric acid) would potentially contribute to the stable formation of whey protein isolate (WPI) emulsion as well as its gel. Thus, in this work, physical stability of seven acid-treated WPI emulsions, and microstructures, rheological properties, water distribution of its emulsion gels were characterized and compared. Initially, the absolute zeta-potential, interfacial protein adsorption, and emulsifying characteristics of acid-induced WPI emulsions were higher in contrast to acid-untreated WPI emulsions. Moreover, acid-induced WPI emulsions were thermally induced (95 ℃, 30 min) to form its emulsion gel networks via disulfide bonds as the main force (acid-untreated WPI emulsions were unable to form gels). High-resolution microscopic observation revealed that acid-induced WPI in emulsion gel network showed the morphology of aggregates. Dynamic oscillatory rheology results indicated that acid-induced emulsion gel exhibited highly elastic behavior and its viscoelasticity was associated with the generation of protein gel networks and aggregates. In addition, PCA and heatmap results further illustrated that malic acid-induced WPI emulsion gels had the best water holding capacity and gel characteristics. Therefore, this study could provide an effective way for the foodstuffs industry to open up new texture and healthy emulsion gels as fat replaces and loading systems of bioactive substances.

Hydrogel delivery systems of functional substances for precision nutrition

Hydrogel delivery systems based on polysaccharides and proteins have the ability to protect functional substances from chemical degradation, control/target release, and increase bioavailability. This chapter summarizes the recent progress in the utilization of hydrogel delivery systems for nutritional interventions. Various hydrogel delivery systems as well as their preparation, structure, and properties are given. The applications for the encapsulation, protection, and controlled delivery of functional substances are described. We also discuss their potential and challenges in managing chronic diseases such as inflammatory bowel disease, obesity, liver disease, and cancer, aiming at providing theoretical references for exploring novel hydrogel delivery systems and their practical prospects in precise nutritional interventions.

Rheology and Extrusion Printing of κ-Carrageenan/Olive Oil Emulsion Gel Tablets with Varying Surface Area to Volume Ratios for Release of Vitamin C and Curcumin

In this work, κ-carrageenan and olive oil at different oil to κ-carrageenan ratios (OCR) are homogenized to create emulsion gels. Interestingly, confocal imaging shows that the oil droplets are stabilized in the κ-carrageenan-structured gel matrix without using any surfactants. Rheological studies show that the oil droplets enhanced the oscillatory yield stress and the maximum printable height of the emulsion gels. The creation of the emulsion gels with an OCR of 1:9-3:7 led to an improvement in the structural integrity of extrusion printed structures. The emulsion gel with an OCR of 3:7 efficiently encapsulates vitamin C in the aqueous phase and curcumin in the hydrophobic oil phase, enabling the extrusion 3D printing of tablets with varying surface area to volume (SA/V) ratios. The release of vitamin C and curcumin is influenced by the preparation method of printing versus casting and the SA/V ratio of the tablets. The hollow cylinder with the highest SA/V ratio was observed to have the highest vitamin C release, whereas for curcumin, the printed tablets had a higher release compared to the cast tablet. Additionally, through rheo-dissolution experiments, we observe a lower modulus and higher vitamin C release from the 3D-printed disc versus the higher modulus and lower vitamin C release from the cast disc tablet.

Stimuli-Responsive Polymers for Engineered Emulsions

Emulsions are complex. Dispersing two immiscible phases, thus expanding an interface, requires effort to achieve and the resultant dispersion is thermodynamically unstable, driving the system toward coalescence. Furthermore, physical instabilities, including creaming, arise due to presence of dispersed droplets of different densities to a continuous phase. Emulsions allow the formulation of oils, can act as vehicles to solubilize both hydrophilic and lipophilic molecules, and can be tailored to desirable rheological profiles, including "gel-like" behavior and shear thinning. The usefulness of emulsions can be further expanded by imparting stimuli-responsive or "smart" behaviors by inclusion of a stimuli-responsive emulsifier, polymer or surfactant. This enables manipulation like gelation, breaking, or aggregation, by external triggers such as pH, temperature, or salt concentration changes. This platform generates functional materials for pharmaceuticals, cosmetics, oil recovery, and colloid engineering, combining both smart behaviors and intrinsic benefit of emulsions. However, with increased functionality comes greater complexity. This review focuses on the use of stimuli-responsive polymers for the generation of smart emulsions, motivated by the great adaptability of polymers for this application and their efficacy as steric stabilizers. Stimuli-responsive emulsions are described according to the trigger used to provide the reader with an overview of progress in this field.

pH/Ion Dual-Responsive Emulsion Via a Cationic Surfactant and Positively Charged Magnesium Hydroxide Nanosheets

Emulsions, formed by dispersing a liquid into another immiscible one by virtue of emulsifiers, have been widely applied in commercial applications like foods, pharmaceuticals, cosmetics, and personal care, which always confront environmental and/or toxic questions due to emulsifiers' high dosage. Recently, a study on Pickering emulsions points out a solution to stable emulsions based on the costabilizing effect of colloidal particles, which focused on surface-active particles cooperating with oppositely charged ionic surfactants. Costabilized emulsions adopting a charge-similar ionic surfactant and particles were less studied. In this article, a hexane-in-water emulsion was prepared in use of a cationic surfactant cetyltrimethylammonium bromide (CTAB) with positively charged magnesium hydroxide (MH) nanosheets at low concentrations (10-5 M and 10-2 wt %, respectively). The emulsion is stable due to the synergy by CTAB and MH nanosheets, which functions in virtue of the electric repulsion by similarly charged particles, the mechanical shielding by MH nanosheets, and restrained water drainage in lamellae between droplets due to the gelation of MH nanosheets. Moreover, the emulsion is doubly switchable within emulsification/demulsification via convenient pH or ion manipulation, a mechanism based on the breakdown and rebuilding of the costabilizing synergy. Such dual-responsive emulsions show high potential for the delicate control of drug delivery, release, and biphasic biocatalysis applications.

Ultrastable High Internal Phase Pickering Emulsions: Forming Mechanism, Processability, and Application in 3D Printing

High internal phase Pickering emulsions (HIPPEs) are versatile platforms for various applications owing to their low-density, solid-like structure, and large specific surface area. Here, naturally occurring polysaccharide-protein hybrid nanoparticles (PPH NPs) were used to stabilize HIPPEs with an internal phase fraction of 80% at a PPH NP concentration of 1.5%. The obtained HIPPEs displayed a gel-like behavior with excellent stability against centrifugation (10000g, 10 min), temperature (4-121 °C), pH (1.0-11.0), and ionic strength (0-500 mM). Confocal laser scanning microscope and cryo-scanning electron microscopy results showed that PPH NPs contributed to the stability of HIPPEs by effectively adsorbing and anchoring on the surface of the emulsion droplets layer by layer to form a dense 3D network barrier to inhibit droplet coalescence. The rheological analysis showed that the HIPPEs possessed a higher viscosity and lower frequency dependence with increasing PPH NP concentration, suggesting the potential application of such HIPPEs in three-dimensional (3D) printing, which was subsequently confirmed by a 3D printing experiment. This work provides highly stable and processable HIPPEs, which can be developed as facile and reusable materials for numerous applications. They can also be directly used for future food manufacturing, drug and nutrient delivery, and tissue reconstruction.

Linear instability analysis of a shear thinning gelled jet with yield stress in coaxial atomization

This study aims to experimentally and theoretically investigate the roles of a threaded nozzle and yield stress in the coaxial air blast atomization of a gelled jet by means of rheological tests and high-speed flow visualization techniques. Similar to the breakup types of Newtonian fluids, a gelled jet will gradually exhibit an oscillation mode, membrane-type breakup, fiber-type breakup and a superpulsating submode as the airflow velocity increases. The transition conditions for each type are determined and plotted in the dimensionless map of We-Oh. For the jet spray angle, the maximum occurs when We = 600 and is clearly enlarged by the gas-side thread in the nozzle. The numerical results of the linear stability analysis indicate that a smaller dominant unstable growth rate is acquired by swelling the yield stress, while the higher dominant unstable growth rate and truncated wavenumber appear as the rotational airflow is acquired through the gas-side threaded nozzle.