Interfacial behavior of cyclodextrins at the oil-water interface of Pickering emulsion

Pickering emulsion stabilized by quercetin-β-cyclodextrin-diglyceride particles: Effect of diglyceride content on interfacial behavior and emulsifying property of complex particles

This research develops diacylglycerol (DAG) based Pickering emulsions with enhanced oxidative stability stabilized by self-assembled quercetin/DAG/β-cyclodextrin (β-CD) complexes (QDCCs) using a one-step agitation method. Influence of DAG content (5%, 15%, 40%, and 80%, w/w) on the self-assembly behavior, interfacial properties, and emulsifying ability of complex particles was investigated. SEM, XRD and ATR-FTIR studies confirmed the formation of ternary composite particles. QDCCs in 80% DAG oil had the highest quercetin encapsulation efficiency (6.09 ± 0.01%), highest DPPH radical scavenging rate and ferric reducing antioxidant property (FRAP). β-CD and quercetin adsorption rates in emulsion with 80% DAG oil were 88.4 ± 2.53% and 98.34 ± 0.15%, respectively. Pickering emulsions with 80% DAG had the smallest droplet size (8.90 ± 1.87 μm) and excellent oxidation stability. This research develops a novel approach to regulate the physicochemical stability of DAG-based emulsions by anchoring natural antioxidants at the oil-water interface through a one-pot self-assembly method.

Influences of ultrasonic treatment on the physicochemical properties and microstructure of diacylglycerol-loaded emulsion stabilized with soybean protein isolate and sodium alginate

This study examined the impacts of ultrasonic power (0, 150, 300, 450, 600, and 750 W) and ultrasonic durations (3, 6, 9, 12, and 15 min) on the physicochemical properties and microstructure of diacylglycerol (DAG)-loaded emulsions stabilized with soybean protein isolate (SPI) and sodium alginate (SA). The findings indicated that the smallest particle size, zeta potential, and contact angle for SPI-SA-DAG emulsions were respectively 5.58 μm, -49.85 mV, and 48.65°, achieved at an ultrasonic power of 450 W. The emulsification properties, loss modulus, storage modulus, and apparent viscosity of the emulsions were optimal at this power setting and at a duration of 9 min. Analytical techniques, including confocal laser scanning-, scanning electron-, and atomic force microscopy, revealed that ultrasonication significantly altered emulsion aggregation state, with the surface roughness (Rq) being minimized at 450 W. These results demonstrated that the stability of SPI-SA-DAG emulsions can be effectively enhanced by an appropriate ultrasonic treatment at 450 W for 9 min. This research provides theoretical support for the broad application of sonication techniques in the food industry.

Different interfaces for stabilizing liquid-liquid, liquid-gel and gel-gel emulsions: Design, comparison, and challenges

Interfaces play essential roles in the stability and functions of emulsion systems. The quick development of novel emulsion systems (e.g., water-water emulsions, water-oleogel emulsions, hydrogel-oleogel emulsions) has brought great progress in interfacial engineering. These new interfaces, which are different from the traditional water-oil interfaces, and are also different from each other, have widened the applications of food emulsions, and also brought in challenges to stabilize the emulsions. We presented a comprehensive summary of various structured interfaces (stabilized by mixed-layers, multilayers, particles, nanodroplets, microgels etc.), and their characteristics, and designing strategies. We also discussed the applicability of these interfaces in stabilizing liquid-liquid (water-oil, water-water, oil-oil, alcohol-oil, etc.), liquid-gel, and gel-gel emulsion systems. Challenges and future research aspects were also proposed regarding interfacial engineering for different emulsions. Emulsions are interface-dominated materials, and the interfaces have dynamic natures, as the compositions and structures are not constant. Biopolymers, particles, nanodroplets, and microgels differed in their capacity to get absorbed onto the interface, to adjust their structures at the interface, to lower interfacial tension, and to stabilize different emulsions. The interactions between the interface and the bulk phases not only affected the properties of the interface, but also the two phases, leading to different functions of the emulsions. These structured interfaces have been used individually or cooperatively to achieve effective stabilization or better applications of different emulsion systems. However, dynamic changes of the interface during digestion are only poorly understood, and it is still challenging to fully characterize the interfaces.

Properties regulation and mechanism on ferritin/chitooligosaccharide dual-compartmental emulsions and its application for co-encapsulation of curcumin and quercetin bioactive compounds

Dual-compartmental emulsions, containing multiple chambers, possess great advantages in co-encapsulation of different cargoes. Herein, we reported a stable dual-compartmental emulsion by regulating the ratio of Marsupenaeus japonicus ferritin (MF) and chitooligosaccharide (COS), enabling efficient co-encapsulation of different compounds. The adsorption behavior of MF/COS complex over droplet interface varied at different ratios, thereby exerting an influence on the emulsion properties. Remarkably, emulsions stabilized by MF/COS complex at a ratio of 2:1 exhibited superior stability, as evidenced by no significant creaming or demulsification during storage or heat treatment. The mechanism is that MF/COS2:1 complex can enhance the formation of thicker interfacial layer and dense continuous phase network structure. Additionally, curcumin and quercetin can be co-encapsulated into the emulsions and their retention rates were significantly improved than those in oils, implying the potential of the resulting dual-compartmental emulsions in co-encapsulation and delivery of bioactive compounds.

Enhanced stability and biocompatibility of HIPEs stabilized by cyclodextrin-metal organic frameworks with inclusion of resveratrol and soy protein isolate for β-carotene delivery

High internal phase Pickering emulsions (HIPEs) constitute a significant research domain within colloid interface chemistry, addressing the demand for robust emulsion systems across various applications. An innovative nanoparticle, synthesized from a cyclodextrin metal-organic framework encapsulated with a composite of resveratrol and soy isolate protein (RCS), was employed to fortify a high internal phase emulsion. The emulsion's three-dimensional printing capabilities, alongside the encapsulated delivery efficacy for β-carotene, were thoroughly examined. Cyclodextrin metal-organic frameworks (CD-MOFs), facilitated by cellulose nanofibrils, were synthesized to yield particles at the nanoscale, maintaining a remarkable 97.67 % cellular viability at an elevated concentration of 1000 μg/ml. The RCS nanoparticles demonstrated thermal stability and antioxidant capacities surpassing those of CD-MOF. The integration of soybean isolate protein augmented both the hydrophobicity (from 21.95 ± 0.64° to 59.15 ± 0.78°) and the interfacial tension (from 14.36 ± 0.46 mN/m to 5.34 ± 0.81 mN/m) of the CD-MOF encapsulated with resveratrol, thereby enhancing the RCS nanoparticles' adsorption at the oil-water interface with greater stability. The durability of the RCS-stabilized high internal phase emulsions was contingent upon the RCS concentration. Emulsions stabilized with 5 wt%-RCS exhibited optimal physical and chemical robustness, demonstrating superior performance in emulsion 3D printing and β-carotene encapsulation delivery. This investigation furnishes a novel perspective on the amalgamation of food customization and precision nutrition.

A Pickering emulsion stabilized by Chitosan-g-Poly(N-vinylcaprolactam) microgels: Interface formation, stability and stimuli-responsiveness

Pickering emulsions stabilized by solid particles are more stable and environmentally friendly compared to traditional surfactants. Herein, a series of Chitosan-g-Poly(N-vinylcaprolactam) (CS-g-PNVCL) microgel particles were synthesized via a free radical surfactant-free emulsion copolymerization and the obtained particles were used to stabilize Pickering emulsions. It is found that the ratio (CS/PNVCL = 60 wt%) was optimal to produce Pickering emulsions. The microstructures of Pickering emulsions can maintain for 60 days at room temperature and this long-term stability is attributed to the CS-g-PNVCL microgel particles adsorbed at the oil-water interface. The Pickering emulsions displayed thermo-responsive characteristics when exposed to environmental stimuli. The emulsions became destabilized with an increase in pH and temperature. The droplets turned unstable and irregular due to excessive NaCl concentration, caused by electrostatic repulsion between the microgel particles. This study presents a novel way to form smart and uniform Pickering emulsions with the application potential in food, cosmetics, and drug delivery, etc.

Fabrication, structure, characterization and emulsion application of citrate agar

In this study, citric acid successfully reacted with agar through the dry heat method, and citrate agar (CA) gel was used to stabilize O/W emulsions. The mechanisms of the CA structure and emulsion pH that affected emulsion stabilization were analyzed, and the application of CA gel emulsion (CAGE) was explored. Compared with native agar (NA), CA showed lower gel strength, higher transparency, and higher water contact angle. These changes indicate that a cross-linking reaction occurred, and it was demonstrated via FTIR and NMR. The emulsion properties were evaluated using particle size, ζ-potential, and the emulsification activity index. Results showed that CAGEs had a smaller particle size and lower ζ-potential than the native agar gel emulsion (NAGE). Meanwhile, confocal laser scanning microscopy confirmed that the CA gels stabilized the emulsions by forming a protective film around the oil droplets. Stability experiments revealed that CAGE (prepared with CA gel [DS = 0.145]) exhibited better stability than NAGE in the pH range of 3-11, and the rheological results further confirmed that the stability of the emulsions was influenced by the network structure and oil droplet interaction forces. Afterward, the application prospect of CAGE was evaluated by encapsulating vitamin D3 and curcumin.

Interfacial adsorption of soybean phosphatidylethanolamine in different oil phase and the stability of water-in-oil emulsion

Water-in-oil (W/O) emulsion holds great potential in designing fat-reduced foods. However, due to the lack of W/O-type surfactant, formation of all-natural W/O emulsion is challenged. This study aimed to investigate the effect of oil phase on interfacial adsorption of soybean phosphatidylethanolamine (SP) and stability of W/O emulsion. Five oils, including medium chain triglycerides oil (MO), coconut oil (CO), palm kernel oil (PKO), sunflower oil (SO) and rapeseed oil (RO), were selected. Results showed that diffusion rate of SP to the interface ranked as MO > CO > PKO > SO ≈ RO, increasing interfacial adsorption from 50.2 % to 85.3 %. Higher interfacial adsorption improved the deformation resistance of interfacial layer, causing more significant decrease in interfacial tension (3.54 mN/m). So, the largest water fraction (65 %) was stabilized by SP with MO and CO, and exhibited smaller droplet sizes and better stability. Consequently, shorter-chain oil was more suitable for preparing W/O emulsions.

Fabrication and characterization of anthocyanin-loaded double Pickering emulsions stabilized by β-cyclodextrin

Anthocyanins, one of the important water-soluble pigments, are sensitive to environmental factors, which limits the application of anthocyanins in food field. In order to overcome this limitation, double Pickering emulsions stabilized by β-cyclodextrin were developed. The optimum preparation conditions of the emulsions were determined firstly and the performance and structure of emulsions were investigated. Results showed that the optimum preparation conditions of emulsions were the ratio of (W1/O): W2 = 6:4 and 4 % β-cyclodextrin concentration. Optical microscope and confocal laser scanning microscope results confirmed that β-cyclodextrin adsorbed onto the surface of droplets forming stable double Pickering emulsions structure. In vitro gastrointestinal digestion experiments proved that double Pickering emulsions played a controlled-release effect in the small intestine. Rheological analysis proved that the emulsions exhibited elastic properties and demonstrated shear thinning behavior. The emulsions showed excellent stability under centrifugation and thermal conditions. These findings will promote anthocyanins' application in daily diet.

β-Cyclodextrin based Pickering emulsions for α-tocopherol delivery: Antioxidation stability and bioaccessibility

β-Cyclodextrin (β-CD) Pickering emulsion and cinnamaldehyde/β-cyclodextrin (CIN/β-CD) Pickering emulsion were prepared and the influences of oxidation and digestion were investigated. CIN/β-CD composite was better dispersed at the oil-water interface than β-CD. Hydrophobic group of CIN anchored in the oil phase and Hydrophilic hydroxyl group of β-CD extended into the aqueous phase, which allowed CIN/β-CD composite to be oriented at the oil-water interface and formed a more stable oil-water interface layer. β-CD Pickering emulsion was more susceptible to oxidative deterioration than CIN/β-CD Pickering emulsion, its malondialdehyde (MDA) value was as high as 509.41 ± 9.37 nmol/L. Digestion experiment indicated that CIN/β-CD Pickering emulsion was released inner oil phase in the small intestine and free fatty acid (FFA) release rate was 44.32 ± 1.08%. Pharmacokinetic parameters manifested that α-tocopherol peak concentration (Cmax) was 64.32 ± 6.45 mg/L and the peak time (Tmax) appeared at 5 h after administration of CIN/β-CD Pickering emulsion.

Effects of physical method and enzymatic hydrolysis on the properties of soybean fiber-rich stabilizer for oil in water emulsions

BACKGROUND

Okara is a by-product from the soybean industry and an abundant resource of insoluble soybean fiber (ISF). ISF with various properties could be obtained by different extraction methods. It is an attractive option to utilize okara by taking advantage of ISF as an emulsifier or stabilizer.

RESULTS

Compared with the untreated ISF (ISFUT ), superfine grinding reduced the particle size and viscosity of ISF (ISFSG ). Steam explosion increased the water solubility from 17.5% to 51.7% but decreased the water holding capacity and swelling capacity of ISF (ISFSE ) from 15.0 and 14.0 g/g to 4.2 and 3.3 g/g, respectively. Emulsions prepared by ISFUT and ISFSG before or after enzymatic hydrolysis presented large oil droplets and were unstable. Although emulsions prepared by ISFSE after enzymatic hydrolysis (ISFSE-E ) showed flocculation, the volume-weighted average diameter (19.7 μm) were the smallest while the viscosity and viscoelastic modulus were the highest, and exhibited excellent physical stability during storage.

CONCLUSION

ISF obtained by physical and hydrolysis treatment displayed diverging physicochemical properties while ISF prepared by steam explosion-enzymatic hydrolysis presented the best potential to stabilize emulsions. The present study could provide novel information about the utilization of okara by the application of ISF as an emulsifier or stabilizer. © 2023 Society of Chemical Industry.

The investigation of thermal stability and GC-MS analysis of Acorus tatarinowii and Atractylodes lancea volatile oils treated by β cyclodextrin inclusion and Pickering emulsion technologies

Objective

To investigate the stability of Acorus tatarinowii and Atractylodes lancea essential oils (ATaAL-EO) under a hot environment at 60 °C, and to analyze the differences in component, quantity, and quality changes, as well as variations in the main components, under different treatment methods of crude oil, β-cyclodextrin inclusion of ATaAL-EO, and Pickering emulsion, to improve the stability and quality of ATaAL-EO.

Methods

The stability of the ATaAL-EO group, the β-cyclodextrin inclusion ATaAL-EO group, and the Pickering emulsion group were investigated under a 60 °C heat environment. Volatile oil retention rate and peroxide value were collected and measured. The volatile oil components of each group were determined by GC-MS, and t-tests were used to screen for differential components. PCA plots for each group were constructed using the OmicShare online platform. Line plots were generated using the Rmisc and reshape2 packages. Upset Venn diagrams under different hot environments were created using the OmicShare online platform to identify quantitative and qualitative changing components and heat map stack plots for newly generated compounds and connected line plots for disappearing compounds were produced for each group. Boxplots for the main component compounds under different hot environments were generated using the reshape2 and ggplot2 packages.

Results

In a hot environment of 60 °C, the β-cyclodextrin inclusion ATaAL-EO and Pickering emulsion group with 1, 3, and 8 h of placement showed higher retention and lower oxidation degree compared to the stability of the ATaAL-EO group. GC-MS analysis results showed that the stability of volatile components in the Pickering emulsion group and β-cyclodextrin inclusion ATaAL-EO group was significantly improved compared to the crude oil group.

Conclusion

β-cyclodextrin inclusion complexes with ATaAL-EO, as well as Pickering emulsions, can significantly enhance the stability and quality of ATaAL-EO. Pickering emulsions have more advantages.

Hydrogen bond recombination regulated by strongly electronegative functional groups in demulsifiers for efficient separation of oil-water emulsions

Tight oil extraction and offshore oil spills generate large amounts of oil-water emulsions, causing serious soil and marine pollution. In such oil-water emulsions, the resin molecules are bound by π-π stacking and bind to interfacial water molecules via hydrogen bonds, which impede the aggregation between water droplets and thereby the separation of the emulsion. In this study, strongly electronegative oxygen atoms (in ethylene oxide, propylene oxide, esters, and hydroxyl groups) were introduced through poly(propylene glycol)-block-polyether and esterification with acrylic acid to attract negative charges in order to form electron-rich regions and enhance interfacial hydrogen bond recombination. The potential distribution in the demulsifier molecules and their space occupancy were regulated by the polymerization reaction to destroy the π-π stacking interaction between resin molecules. The results show that the binding energies (binding free energy and hydrogen bonding energy) of oxygen-containing demulsifier molecules with water molecules were higher than those of resin molecules with water molecules, resulting in the fission of the hydrogen bonds between resin and water molecules. The introduction of demulsifier molecules that occupied large interfacial space reduced the binding energy between resin molecules from -2176.06 to -110.00 kJ·mol-1. Noteworthy, the binding energy between demulsifier molecules and resin molecules was -1076.36 kJ·mol-1 lower than that between resin molecules (-110.00 kJ·mol-1), indicating the adsorption of the surrounding interfacial resin molecules by the demulsifier molecules and destruction of the π-π stacking between them, thus favoring the collapse of the interfacial structure of the oil-water emulsion and achieving its separation. This study provides important theoretical support for the treatment of oil-contaminated soil and offshore oil spill pollution.

Combination of carrageenan with sodium alginate, gum arabic, and locust bean gum: Effects on rheological properties and quiescent stabilities of partially crystalline emulsions

In the present study, carrageenan (CG) was combined with sodium alginate (SA), gum arabic (GA), and locust bean gum (LBG) to obtain four gum combinations (CG, CG + SA, CG + GA, and CG + LBG). The effects of different combinations on rheological properties and quiescent stabilities of PCEs were systematically investigated through characterization of fresh emulsion related parameters (rheological properties, forces between proteins, zeta potentials, surface tensions, interfacial adsorption properties, and multiple light scattering) and storage related parameters (visual appearance, creaming index, viscosities, particle sizes, and microscopic morphology). Rheological results indicated that CG PCEs had the highest apparent viscosities of 7.77-41.91 Pa·s at 0.01 s-1, followed by CG + SA PCEs (2.35-30.62 Pa·s), CG + GA PCEs (2.37-21.16 Pa·s), and CG + LBG PCEs (2.06-19.93 Pa·s). At low thickener concentration (0.02 %), CG PCE exhibited weak gel structure due to higher G' than G″ at all frequencies, while CG + SA, CG + GA, and CG + LBG PCEs had entangled network due to intersection between G' and G″. After three months of storage, CG + SA PCEs showed the lowest creaming index values (11.47-17.75 %), which were significantly lower than CG PCEs (15.35-20.85 %), CG + GA PCEs (15.97-24.42 %), and CG + LBG PCEs (17.13-21.71 %). Meanwhile, all the samples except for 0.02 % CG + SA PCE completely lost fluidity, and their viscosities were above 14,000 mPa·s. It was further found that CG stabilized emulsions showed severe droplet flocculation induced by hydrophobic interactions among adsorbed proteins. Combination of CG with SA, GA, and LBG, especially CG + SA, formed strong network structure and reduced contribution of hydrophobic interactions, which effectively inhibited flocculation of fat droplets, thereby improving rheological properties and storage stabilities of PCEs.

Particle-Polymer Union with Changeable Wettability for Constructing Bijels Using a Simple Mixing Method

Bicontinuous emulsion gels (bijels) are nonequilibrium dispersed systems with particle-stabilized continuous fluid domains, and the internal connectivity of channels brings the possibility of efficient mass transport, endowing bijels great potential in diverse applications. Different from the common method to produce bijels, the spinodal decomposition, which needs precise temperature control and is restricted by the selection of liquid pairs, in this work, a direct mixing method was performed to construct bijels, simplifying the fabrication process. The hydrophilic rod-shaped cellulose nanocrystalline (CNC) particles were in situ combined with the hydrophobic polymer, aminopropyl-terminated polydimethylsiloxane (PDMS-NH2), to acquire a controllable interfacial wettability of CNC. The CNC@mPDMS-NH2 complexes were adsorbed at the water-toluene interface and achieved a change of Pickering emulsion types, oil-in-water, bijel, and water-in-oil, through tuning the interfacial performance of CNC@mPDMS-NH2 complexes. A three-dimensional scanning image and curvature calculation were applied to verify the obtained bijel, further demonstrating the successful preparation of the bicontinuous structure. This work enriched the members of particles for stabilizing bijels and was considered to be scalable in manufacturing for applications on a large scale.

Interfacial Rheological and Emulsion Properties of Self-Assembled Cyclodextrin-Oil Inclusion Complexes

To investigate the effect of the molecular size of alkanes and the cavity size of cyclodextrins (CDs) on the formation of interfacial host-guest inclusion complexes, the interfacial tension (IFT) of CD (α-CD, β-CD, γ-CD) solutions against oils (hexadecane, dodecylbenzene) was determined by interfacial dilational rheology measurements. The results show that the "space compatibility" between CDs and oil molecules is crucial for the formation of interface host-guest inclusion complexes. Hexadecane with a smaller molecular size can form host-guest inclusion complexes with small cavities of α-CD and β-CD, dodecylbenzene with a larger molecular size can form interfacial aggregates with the medium-sized cavity of β-CD easily, and the polycyclic aromatic hydrocarbon molecules in kerosene can form inclusion complexes with the large cavity of γ-CD. The formation of interfacial inclusion complexes leads to lower IFT values, higher interfacial dilational modulus, nonlinear IFT responses to the interface area oscillating, and skin-like films at the oil-water interface. What's more, the phase behavior of Pickering emulsions formed by CDs with different oils is explored, and the phenomena in alkane-CD emulsions are in line with the results in dilatation rheology. The interfacial active host-guest structure in the kerosene-γ-CD system improves the stability of the Pickering emulsion, which results in smaller emulsion droplets. This unique space compatibility characteristic is of great significance for the application of CDs in selective host-guest recognition, sensors, enhanced oil recovery, food industries, and local drug delivery.

Modulating hydrophilic properties of β-cyclodextrin/carboxymethyl cellulose colloid particles to stabilize Pickering emulsions for food 3D printing

This research investigated edible Pickering emulsions stabilized by polysaccharide complexes as inks for food 3D printing. The interface membrane structure in the Pickering emulsion system was formed using complexes consisting of β-cyclodextrin (β-CD) and carboxymethyl cellulose (CMC). Except for provide sufficient steric barrier and electrostatic repulsion to increase the stability of the Pickering emulsions, the interface membrane constructs also can demonstrate good biphasic wettability and lower oil/water interfacial tension. The hydrophilicity of complexes (β-CD/CMC) was mainly adjusted by the ratio of β-CD/CMC (R_β/C) and the substitution degree (DS) of CMC, which further adjusted the physical and chemical properties of Pickering emulsion to make it correspond to the rheological behavior applied to 3D printing. The stable Pickering emulsion (R_β/C = 2:2, DS = 1.2, weight ratio of oil phase (φ) = 65 %) displayed excellent printing potential by characterizations analysis of Pickering emulsions. The smoothness, viscosity, and self-supporting ability of the Pickering emulsion under the optimized conditions were further analyzed using a filling density printing experiment of a cuboid model. The emulsifying properties of β-CD were adjusted by hydrophilic CMC to achieve the required amphipathic properties of the complexes to develop Pickering emulsions for food 3D printing.