Emulsion Structure Research Articles

W/o/w multiple emulsions: A novel trend in functional ice cream preparations?

Ice cream is a popular product worldwide. Unfortunatelly, it contains a significant amount of fat. In this review, promising strategies for the use of w/o/w multiple emulsion structures in creams are assessed. W/o/w multiple emulsions (MEs) enable reduction the fat without losing the creamy taste and mouthfeel and also encapsulation of sensitive compounds. The encouraging application and formation of MEs in ice cream mixtures is supported by the use of natural food ingredients, such as fiber, which helps to stabilize the whole system and improves nutritional value. The future trends may be focused on the target stabilizations using Pickering paticles (PPs). The possible advantages, manufacture, evaluation methods, and predicted future prospects of MEs in ice creams are discussed.

Evaluation of membrane quality and entrance pressure of oil-based mud at elevated temperatures

AbstractThis study fully explored the impact of temperature on the membrane quality of oil-based mud (OBM) using static gravimetric measurements, membrane efficiency and entrance pressure tests. More than 30 shale samples were used to assess the membrane behavior of several OBMs under elevated temperatures. Results suggested that OBM acted as a semi-permeable membrane at low temperatures (25–55˚C) since ion flow out of OBM and into shale was restricted despite the existence of a large ionic concentration gradient, while water flowed freely out of shale and into OBM because of the existence of a chemical potential difference. For temperatures higher than 55˚C, relatively higher ion flux into shale and slightly lower water flow out of shale was observed. Excessive heat may have possibly destabilized or even destroyed the emulsifier's structure that serves as a mechanism through which OBM performs as a semi-permeable membrane. The instability of OBM's emulsifier was further confirmed through entrance pressure testing where an appreciable reduction in entrance pressure of OBM was measured at high temperatures.

Soy protein-based delivery systems as carriers of trans-resveratrol: Bioaccessibility using different in vitro digestion models

Ingestion of trans-resveratrol promotes health benefits, but the low solubility and chemical stability of this compound may hamper its bioaccessibility. To overcome these drawbacks, O/W emulsions loaded with resveratrol (liquid or gelled) and stabilized by soy protein isolate (SPI) were used to protect and vehiculate the bioactive compound to the target absorption site. Two distinct strategies were used to allow protein denaturation: heating the A) aqueous phase of the emulsion before homogenization; or B) emulsion after homogenization. Delivery efficacy of resveratrol was evaluated by static or semi-static in vitro digestion assays. For the semi-static approach, a dynamic gastric model was developed that was able to simulate the intensity of contraction forces and the gradual decrease of pH in the gastric step in vivo. The structure of the liquid emulsions remained similar in the static and semi-static digestion approaches, showing little influence of peristalsis on droplet size. The gelled emulsions showed breakdown of the gel network in the presence of the mechanical forces of the semi-static tests, although its structure was not completely degraded at the end of the in vitro digestibility tests. Anyway, the results of bioaccessibility of the carriers were similar (around 70–75%) and high, being these emulsions effective carriers of resveratrol. However, the bioaccessible fraction of liquid emulsions was much higher after digestion under static conditions, showing the relevance of developing dynamic systems for a more realistic simulation of in vitro digestion processes.

A review of recent progress in improving the bioavailability of nutraceutical-loaded emulsions after oral intake.

Increasing awareness of the health benefits of specific constituents in fruits, vegetables, cereals, and other whole foods has sparked a broader interest in the potential health benefits of nutraceuticals. Many nutraceuticals are hydrophobic substances, which means they must be encapsulated in colloidal delivery systems. Oil-in-water emulsions are one of the most widely used delivery systems for improving the bioavailability and bioactivity of these nutraceuticals. The composition and structure of emulsions can be designed to improve the water dispersibility, physicochemical stability, and bioavailability of the encapsulated nutraceuticals. The nature of the emulsion used influences the interfacial area and properties of the nutraceutical-loaded oil droplets in the gastrointestinal tract, which influences their digestion, as well as the bioaccessibility, metabolism, and absorption of the nutraceuticals. In this article, we review recent in vitro and in vivo studies on the utilization of emulsions to improve the bioavailability of nutraceuticals. The findings from this review should facilitate the design of more efficacious nutraceutical-loaded emulsions with increased bioactivity.

Novel strategy for color-controllable Pickering emulsion: Location control of pigments at different phase

To develop a novel strategy for preparing color-controllable emulsion by controlling pigments spatial location, the stable Pickering emulsion (O/W) was firstly established by using zein-chitosan nanoparticles (ZCNPs) as outer layer and medium chain triglyceride as inner phase. Three fat-soluble pigments (FSPs), curcumin, oil red and oil blue, were introduced into this emulsion system by controlling their location (in outer layer or inner phase). The physical properties, qualitative and quantitative color analysis of the emulsion were investigated by encapsulation efficiency, confocal laser scanning microscope and values of L*a*b*. The loading efficiency of ZCNPs to FSPs maintained at 87.6%–89.3%, and had 95% of oil encapsulation efficiency. Different from the blending coloring strategy, the emulsions formed in this paper showed better chroma (based on L*a*b* values) with even fewer additive pigments amount. Under the same amount of pigment, the saturation of the emulsion (FSPs in outer layer) could increase by 81.5%. This study might provide a new color control strategy for complex food systems. • The structure of Pickering emulsion was defined as outer layer or inner phase. • ZCNPs had a higher loading efficiency for the three FSPs. • Pickering emulsion stabilized by ZCNPs was stable. • Color could be adjusted by changing the location of pigments in the emulsion. • The emulsion color was more susceptible to outer layer.

Preparation, characterization and in vitro digestive behaviors of emulsions synergistically stabilized by γ-cyclodextrin/sodium caseinate/alginate

Developing natural, safe, and biocompatible emulsion stabilizers for highly stable emulsions remains a difficult challenge. In this study, stable nano-scale emulsions were prepared using γ-cyclodextrin (γ-CD), sodium caseinate (SC), and alginate (Alg) as emulsifiers. The synergistic stabilization of γ-CD/SC/Alg enabled the emulsions to remain stable even under high-acidic (pH 3.0), high-alkaline (pH 11.0) and high temperature (90 °C) conditions. The improved stability at acidic conditions was attributed to the positive impact of Alg. Additionally, the rheological measurements showed that the emulsions exhibited elastic gel networks and a more stable emulsion structure was formed with the increasing addition of γ-CD. Finally, the gastrointestinal behavior of the emulsions was studied using a standardized INFOGEST method. Results showed that most of the oil were digested and absorbed in the small intestine, and the bioaccessibility of curcumin was high. This work provided a new solution to prepare stable emulsions which could be used as dairy products or desirable food delivery systems for hydrophobic bioactive agents.

Fabrication and characterization of gel-in-oil-water (G/O/W) double emulsion stabilized by flaxseed gum/whey protein isolate complexes

The aim of this study was to fabricate stable water-in-oil-in-water double emulsions with gelled internal water phase (G/O/W emulsion). The polyglycerol polyricinoleate (PGPR) was used as the lipophilic emulsifier and flaxseed gum (FG) /whey protein isolate (WPI) electrostatic complexes were used as the hydrophilic emulsifier. The rheological results showed that W1 became gelled when the FG concentration reached 0.4 wt%. Increased concentrations of FG in W1 significantly enhanced the stability of W1/O/W2 emulsions, accompanied with the diminution in droplet size and increased viscosity. It could be attributed to the strong interfacial activity and thickening effect of FG. Optical and confocal microscopy confirmed the formation of W/O/W emulsion structure and supported the particle size results. The maximum complex formation between FG and WPI occurred at pH 3.8, with the mass ratio of 1:1. In comparison to WPI, the complex of FG/WPI exhibited a significant improvement in the stability of G/O/W double emulsions. The storage stability test showed that the G/O/W emulsion fabricated with 0.8 wt% FG and 0.5 wt% FG/WPI complexes showed the highest stability without phase separation or oil-off phenomenon within 28 days. Consequently, the incorporation of FG (≥0.4 wt%) in W1 and utilization of FG/WPI complexes could be considered as a new strategy for obtaining W/O/W emulsions with long-term storage stability.

Effect of humectants and Zygosaccharomyces bailii inoculation on the physical stability of oil-in-water emulsions modeling salad dressings.

Salad dressing formulations include a pH within 3.2-4.1, salt and other solutes to depress water activity. The interaction between hydrocolloids and other components such as humectants determines their physical and microbiological stability. To our knowledge, the effect of commonly used solutes on physical stability and rheological characteristics of oil-in-water emulsions stabilized by xanthan gum has not been reported, and neither has the effect of a spoilage yeast on physical stability been evaluated. The effect of different humectants (sodium chloride, glucose and xylitol) and Zygosaccharomyces bailii inoculation on the stability of oil-in-water emulsions containing different levels of xanthan gum to emulate different types of salad dressings was investigated by means of droplet size, zeta potential, rheological measurements and confocal laser scanning microscopy (CLSM). Generally, the addition of humectants strengthened the weak or strong emulsion structure, especially xylitol. Glucose or xylitol acted as stabilizers since they decreased Sauter and De Broucker diameter. On the contrary, NaCl destabilized the emulsions since it increased droplet size and exhibited the lowest absolute values of zeta potential. Inoculation with Z. bailii destabilized some emulsions since it increased Sauter and De Broucker diameter. Emulsion droplet size, polydispersity, and xanthan gum and yeast location were confirmed by CLSM imaging. This study highlights the key role of humectants and xanthan gum level on physical characteristics and stability of oil-in-water emulsions. Addition of xylitol leads to an enhancement in emulsion rheology and physical stability, suggesting that it is a potential low-calorie multifunctional additive for salad dressings. © 2022 Society of Chemical Industry.

Fabrication of gel-like emulsions with γ-zein particles using microfluidization: Structure formation and rheological properties

In this work, γ-zein, which is a type of cysteine rich prolamine in corn, was prepared into particles for fabricating stable gel-like emulsions. The effects of homogenization pressure (0.1–120 MPa) on structure formation and rheological properties of emulsions were systematically studied. Microscopy showed that γ-zein particles provided stabilization at droplet interfaces, and that excess protein particles provided a particle network in continuous phase, and microfluidization significantly decreased droplet size and induced to form droplet clusters and gel-like network. With an increase of homogenization pressure, protein content adsorbed at droplet interfaces and entrapped within gel-like structure of emulsions increased, and more hydrophobic interactions and disulfide bonds between protein particles were formed. As a result, stronger gel strength of emulsions were observed, for example, apparent viscosity, storage modulus (G'), loss modulus (G''), and G'/ G'' crossover strain (γco) increased, the frequency dependency of G' (n, G′ ∼ ωn) decreased. Also, Lissajous curves were used to further understand the non-linear viscoelastic behavior of these emulsions. Emulsions prepared without microfluidization (control, 0.1 MPa) showed a weak gel structure with viscous-dominating behavior at high strain, while emulsions prepared with microfluidization showed predominantly elastic behavior at low strain, and plastic-dominating behavior at high strain. These findings showed that cysteine rich protein based- emulsion gels with tunable microstructure and rheological properties can be easily produced by controlling the homogenization pressure.

Preparation of core-shell microcapsules based on microfluidic technology for the encapsulation, protection and controlled delivery of phycocyanin

Phycocyanin (PC) is a naturally active protein with extensive potential physiological functions. However, the poor stability and low bioavailability of PC have limited its development in nutraceuticals. Therefore, we developed an efficient microfluidic device to fabricate core-shell microcapsules for PC entrapment and colonic delivery. Microfluidics utilizes microchannels and fluid flow rates to shear mutually incompatible fluids to form dispersed emulsion droplets, providing an opportunity to investigate the structure and size of emulsions and precisely control the production of emulsion droplets. By introducing intermolecular interactions, PC was effectively immobilized in the cavity of the inner core sodium alginate (SA) gel, ensuring a high encapsulation efficiency of up to 98% for SA-E microcapsules. The release effects of microcapsules with different wall thicknesses were evaluated by simulating gastrointestinal juice digestion experiments. The results revealed that the microcapsules with 20–30 μm wall thickness were more stable and had superior release performance in gastrointestinal fluid compared with the microcapsules with 10 and 50 μm wall thickness. In addition, after the simulated digestion process in artificial gastrointestinal fluid, the PC embedded in SA-E microcapsules still remained the same structure and exhibited good antioxidant and immunomodulatory activities. The enhanced stability and bioavailability of PC suggested that SA-E microcapsules can be used for PC entrapment and colonic delivery.

Modulation of the spatial distribution of crystallizable emulsifiers in Pickering double emulsions

The unique role of the spatial distribution of crystallizable emulsifiers in regulating the structure and properties of double emulsions has been gradually recognized. Herein, we utilized crystallizable monoglycerides of different carbon chain length (GMS/GMP/GML) to “structuring” the intermediate oil phase of double emulsions during a two-stage emulsification process followed by a cooling treatment. A ternary eigenvector (I, M, E) based on the numerical processing of polarization images was invented to quantitatively characterize the distribution pattern of monoglycerides. Crystallization kinetics analysis and dissipative particle dynamic simulation were then employed to reveal the regulatory mechanism for the site-specific interface distribution behavior. Results suggested that the distribution pattern of monoglycerides could be pricesly tuned as the internal interface-, external interface- or oil-phase dominated one in double emulsions. The surface activity as well as crystallization rates of monoglycerides dominated the interfacial distribution kinetics, and the cooling gradient along the interface region further regulated their interfacial distribution potential. Specificly, shorter crystallization time (t1/2) made GMP molecules rapidly solidified in oil phase, leading to the oil phase domninate crystallization (0, M, 0), whereas, slow crystallization rate rendered GML and GMS with sufficient time to diffuse to the interface, thus forming interfacial crystals ((I, 0, 0) and (0, 0, E)). The sensitivity of GML to cooling gradient along the interface region led to its preferential external interface distribution under cooling treatment. The presented study explored novel strategies that can be used in characterizing and manipulating the distribution pattern of crystallizable emulsifiers in multi-interface emulsion systems.

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.

Improved functionality of cinnamon oil emulsion-based gelatin films as potential edible packaging film for wax apple

This study discusses on the tailoring of cinnamon oil emulsion-based gelatin edible films that can encapsulate, protect and release bioactive compounds in food packaging applications. The effect of this cinnamon oil film for shelf-life extension and storage stabilities of wax apples (Syzygium samarangense L.) was evaluated over 12-day storage at refrigerated temperature (5 °C). Emulsion of cinnamon oil and surfactant at different ratios of 70:30 (ME1), 60:40 (ME2) and 50:50 (ME3) was incorporated into the films and the interactions between the emulsion and polymeric structure in films were analysed through physical, morphological and functional properties. The cinnamon oil emulsion-based gelatin films with a ratio of 70:30 exhibited significant increase in mechanical, water barrier, antioxidant activity and thermal stability. The increase in antioxidant activity of cinnamon oil films revealed that encapsulation of cinnamon oil in gelatin matrix better retains the bioactive compounds for food packaging applications. Cinnamon oil emulsion-based films significantly lowered the weight loss of wax apples (12.43%) compared to the control (unwrapped) wax apples (26.40%). Interestingly, this research indicates that encapsulation of bioactive compounds is governed by the ratio of oil to surfactant mixture in emulsion. It was proved that the film microemulsion with the 70:30 ratio of oil to surfactant (FME 70) have better overall performances as compared to the control (gelatin films) due to hydrogen and hydrophobic interactions with protein network of gelatin. In conclusion, cinnamon oil emulsion-based films could enhance and modify the functionality of protein-based films creating a biodegradable, sustainable and cost-effective food packaging materials.

Spontaneous patterning method utilizing transformation of UV-curable emulsion

A self-organizing structure is important for imparting functions and simplifying the manufacturing process. The development of spontaneous structures with a roll-to-roll process capability is a challenging task. We propose a novel patterning method utilizing the destruction of the emulsion structure. An oil-in-water (O/W) UV-curable emulsion liquid film was partially exposed to UV, resulting in aggregation and immobilization of the emulsion in the medium. Emulsion droplets in the unexposed area are coalesced by removing water. Coalesced emulsion droplets expand and spontaneously permeate into the pores formed in the aggregated structure of UV-cured emulsion particles, causing an uneven structure. An uneven pattern can be formed by direct UV exposure of the liquid film and the subsequent drying process without requiring a development process.

The Influence of Cellulose Ethers on the Physico-Chemical Properties, Structure and Lipid Digestibility of Animal Fat Emulsions Stabilized by Soy Protein.

This study explores the influence of carboxymethylcelullose (CMC) and methylcelullose (MC), added by simultaneous (sim) and sequential (seq) emulsification methods, on the structure, rheological parameters and in vitro lipid digestibility of pork lard O/W emulsions stabilized by soy protein concentrate (SPC). Five emulsions (SPC, SPC/CMC-sim, SPC/CMC-seq SPC/MC-sim, SPC/MC-seq) were prepared in vitro. The presence of CMC and MC, and the stage of incorporation affected the emulsion microstructure. In the SPC emulsion, lipid droplets were entrapped by a protein layer that was thicker when MC was added, providing greater resistance against environmental stresses during gastrointestinal digestion. At 37 °C, CMC incorporation produced a structural reinforcement of the SPC emulsion, whereas MC addition did not affect the network rigidity, although a delaying effect on the crossover temperature was observed, which was more evident in SPC/MC–seq. The presence and stage of CMC and MC incorporation affected the rate and extent of lipolysis, with SPC/MC-seq presenting an inferior concentration of free fatty acids. The lower extent of lipolysis observed in SPC/MC-seq may be positive in the manufacture of animal fat products in which reduced fatty acid absorption is intended.

Encapsulation of Bacillus thuringiensis in an inverse Pickering emulsion for pest control applications

Here, we present an inverse Pickering emulsion-based formulation for Bacillus thuringiensis serovar aizawai (BtA) encapsulations utilized towards pest control applications. The emulsification was carried out by high shear homogenization process via ULTRA-TURRAX®. The water-in-mineral oil emulsions were stabilized by commercial hydrophobic silica. Different silica contents and water/oil ratios were studied. Stable emulsions were obtained at 2 and 3 wt% silica at 30% and 20% water volumes, respectively. The structure of the Pickering emulsions were characterized by laser scanning confocal microscopy and cryogenic scanning electron microscopy. The BtA cells, spores and crystals were encapsulated in the water droplets of the inverse Pickering emulsions. An emulsion composed of 3 wt% silica and 30% water was found to be the most suitable for encapsulation. The pest control efficiency of the encapsulated BtA against Spodoptera littoralis first instar larvae was tested. The studied BtA/emulsion system exhibited a mortality rate of 92%. However, the non-formulated BtA has shown 71% mortality, and the emulsion alone resulted in only 9% mortality. These findings confirm that an emulsion with encapsulated BtA can function as an efficient formulation for biopesticides.

Modulation of viscosity, microstructure and lipolysis of W/O emulsions by cellulose ethers during in vitro digestion in the dynamic and semi-dynamic gastrointestinal models

In this study, W/O emulsions incorporated with various proportions of two hydrocolloids, namely, methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC), were prepared. The shear viscosity, microstructure, and lipolysis of the W/O emulsions before and during in vitro digestion in the dynamic (DIVHS) and semi-dynamic gastrointestinal models were evaluated and compared. The shear viscosity of both emulsions increased with the addition of MC and HPMC content up to a certain limit (0.5–2%), whereas it significantly decreased at a higher addition level (4%) due to the increased flocculation and coalescence in higher cellulose ethers. The HPMC emulsions (2 wt % in aqueous phases) showed higher viscosity and larger droplet size than the equivalent MC emulsions before and during simulated digestion, accompanied by the lower extent of lipolysis. These results are in line with the formation of a more compact and stronger gel structure in HPMC emulsions, which could retard lipase adsorption at the W–O interface. For both emulsions at the same concentration (40 wt%), a higher extent of free fatty acid (FFA) release was found during digestion in the dynamic system (HPMC ꞊ 62%, MC ꞊ 72%) compared to that in the semi-dynamic model (HPMC ꞊ 58%, MC ꞊ 70%). This behavior was supported by the smaller droplet size of emulsions digesta collected from the dynamic system having a larger surface area. Overall, the present study suggested that the dynamic DIVHS system was more effective in enzymatic hydrolysis of the W/O emulsions investigated than the semi-dynamic model under the current experimental conditions. This work had provided valuable insights into the modulation of the structural and digestive properties of W/O emulsions by the addition of MC and HPMC, which could be meaningful for the development of healthier emulsion-based food products (e.g., margarine and spreads) with reduced lipid digestibility.

Feasible Digital Light Processing Three-Dimensional Printing of a Biodegradable Porous Polymer with a High Internal Phase Emulsion Structure

Feasible Digital Light Processing Three-Dimensional Printing of a Biodegradable Porous Polymer with a High Internal Phase Emulsion Structure

Nanocellulose from bamboo shoots as perfect Pickering stabilizer: Effect of the emulsification process on the interfacial and emulsifying properties

In this work, the medium internal phase O/W Pickering emulsions stabilized with bamboo shoots nanocellulose (BSNC) was successfully fabricated. The nanocellulose extracted from bamboo shoots with an average width of 56.37 nm and height of 7.44 nm showed great potential as an emulsifier in the Pickering emulsions. The effects of BSNC content, oil-water ratio and emulsification process on the structure, stability and rheology of the resultant Pickering emulsions was explored. The obtained emulsion with the BSNC content of 0.5 wt% at the oil to water volume ratio of 5:5 had a lower particle size of around 25 μm. With the increasing BSNC content, the emulsions presented increased droplet size, and even demulsification occurred. Interestingly, the physicochemical properties of the emulsions could be significantly improved through twice shearing, which effectively reduced droplet size. The surface coverage was above 100% for the Pickering emulsions stabilized with the BSNC content of 0.5%–1.1%. With the increasing BSNC content, the apparent viscosity was increased first and then decreased, and all emulsions showed elastic behaviors. This work would provide theoretical guidance for preparing medium or high internal phase Pickering emulsions stabilized with nanocellulose.

Nanosheet-Stabilized Emulsions: Near-Minimum Loading and Surface Energy Design of Conductive Networks.

Here, we develop a framework for assembly, understanding, and application of functional emulsions stabilized by few-layer pristine two-dimensional (2D) nanosheets. Liquid-exfoliated graphene and MoS2 are demonstrated to stabilize emulsions at ultralow nanosheet volume fractions, approaching the minimum loading achievable with 2D materials. These nanosheet-stabilized emulsions allow controlled droplet deposition free from the coffee ring effect to facilitate single-droplet devices from minute quantities of material or assembly into large-area films with high network conductivity. To broaden the range of compositions and subsequent applications, an understanding of emulsion stability and orientation in terms of surface energy of the three phases is developed. Importantly, this model facilitates determination of the surface energies of the nanosheets themselves and identifies strategies based on surface tension and pH to allow design of emulsion structures. Finally, this approach is used to prepare conductive silicone emulsion composites with a record-low loading level and excellent electromechanical sensitivity. The versatility of these nanosheet-stabilized emulsions illustrates their potential for low-loading composites, thin-film formation and surface energy determination, and the design of functional structures for a range of segregated network applications.