Stable Pickering Emulsions Research Articles

Preparation, characterization and stability of water-in-oil Pickering emulsions stabilized by acylated EGCG derivatives

Excessive intake of trans and saturated fatty acids from solid fats contributes to the development of chronic diseases. Food-grade water-in-oil (W/O) emulsions for the replacement of trans and saturated fat products, delivery of active compounds and microreactors remain to be further explored. Camellia oil-based W/O Pickering emulsions were prepared using acylated EGCG derivatives with various carbon chain lengths, including EGCG myristate (MYR-E), EGCG palmitate (PAL-E), and EGCG stearate (STEA-E). The acylated EGCG derivatives exhibited a contact angle of 90–100° with water droplets and could theoretically be used as Pickering emulsion stabilizers. The acylated EGCG derivatives were dissolved in the oil phase as needle-like crystals, which stabilized the emulsion against aggregation by adsorption at the oil-water interface. Pickering emulsions developed with STEA-E (PE-STEA) maintained higher stability after three freeze-thaw cycles, with a creaming index (CI) of 0% at oil-water volume ratios greater than 4:6. PE-STEA with varying oil-water volume ratios were stable at room temperature and 4 °C after long-time storage, with a maximum CI of only 1.39%. This study could provide new perspectives on the application of acylated EGCG derivatives and broaden the application of surfactant-free W/O Pickering emulsions in the food industry.

Tunability of Pickering particle features of whey protein isolate via remodeling partial unfolding during ultrasonication-assisted complexation with chitosan/chitooligosaccharide

The potential of ultrasonication-driven molecular self-assembly of whey protein isolate (WPI) with chitosan (CS)/chitooligosaccharide (COS) to stabilize Pickering emulsions was examined, based on CS/COS ligands-induced partial unfolding in remodeling the Pickering particles features. Multi-spectral analysis suggested obvious changes in conformational structures of WPI due to interaction with CS/COS, with significantly higher unfolding degrees of WPI induced by COS. Non-covalent interactions were identified as the major forces for WPI-CS/COS conjugates. Ultrasonication enhanced electrostatic interaction between CS's -NH3 groups and WPI's -COO− groups which improved emulsification activity and storability of WPI-COS stabilized Pickering emulsion. This was attributed to increased surface hydrophobicity and decreased particle size compared to WPI-CS associated with differential unfolding degrees induced by different saccharide ligands. CLSM and SEM consistently observed smaller emulsion droplets in WPI-COS complexes than WPI-CS/COS particles tightly adsorbed at the oil-water interface. The electrostatic self-assembly of WPI with CS/COS greatly enhanced the encapsulation efficiency of quercetin than those stabilized by WPI alone and ultrasound further improved encapsulation efficiency. This corresponded well with the quantitative affinity parameters between quercetin and WPI-CS/COS complexes. This investigation revealed the great potential of glycan ligands-induced conformational transitions of extrinsic physical disruption in tuning Pickering particle features.

Characterization of methyltetrahydrophthalic anhydride esterified corn starch and their ability in stabilizing Pickering emulsion

Methyltetrahydrophthalic anhydride (MeTHPA) esterified corn starches (MeCS) with degrees of substitution (DS) of 0.0066–0.072 were prepared, characterized and applied to stabilize Pickering emulsion. Fourier transform infrared spectroscopy analysis revealed the presence of a new ester group in MeCS. MeTHPA modification damaged the crystal structure of the corn starch, made its surface structure rough and irregular, and increased its contact angle. These changes were positively correlated with the DS of MeCS. Compared to native corn starch, the particle size of MeCS increased first and then decreased with an increase in DS, the lowest value (4.67 ± 0.08 μm) was observed for MeCS with highest DS (0.072). The stability of Pickering emulsions stabilized by MeCS with a DS of 0.072 was better than those stabilized by MeCS with lower DS (0.0066–0.019), which may attribute to their smaller particle size and higher viscosity. MeCS (DS 0.072) as emulsifiers at a concentration of 3% (w/v) could keep the emulsion stable even after 50 days of storage. This research suggested that MeCS at proper DS and concentration levels may serve as effective particle stabilizers for Pickering emulsions.

Low-Frequency Ultrasound Effects on Cellulose Nanocrystals for Potential Application in Stabilizing Pickering Emulsions.

Cellulose, in the form of cellulose nanocrystals (CNCs), is a promising biomaterial for stabilizing Pickering emulsions (PEs). PEs are commonly formed using low-frequency ultrasound (LFU) treatment and impact CNC properties. The present study investigated the specific effects of LFU treatment on CNCs' chemical and physical properties. CNCs were characterized using dynamic light scattering, ζ;-potential determination, Fourier transform infrared spectroscopy, X-ray diffraction, and contact angle measurement. CNC suspensions were studied using rheological analysis and static multiple light scattering. LFU treatment broke CNC aggregates and modified the rheological behavior of CNC suspensions but did not affect the CNCs' chemical or crystallographic structures, surface charge, or hydrophilic properties. During the storage of CNC suspensions and PEs, liquid crystal formation was observed with cross-polarized light. Hypotheses related to the impact of liquid crystal CNCs on PE stability were proposed.

Plant protein and animal protein‐based Pickering emulsion: A review of preparation and modification methods

AbstractProtein‐based Pickering emulsions are gaining popularity due to their biocompatibility and alignment with people's pursuit of health. This review focuses on recent advances in the preparation of Pickering emulsions using various plant and animal proteins from different sources. For sustainability and cost reasons, plant proteins are preferred, while animal proteins provide better nutritional quality. According to the type of plant or animal protein, the suitable modification and preparation methods of stable Pickering emulsion are summarized, including heating, enzyme induction, anti‐solvent precipitation, pH‐cycling, glycosylation, microwave heating, spray drying, and high hydrostatic pressure. Different methods were employed to modify the properties of Pickering emulsion particles at the oil–water interface. To overcome the amphiphilicity limitations of some proteins, substances such as polysaccharides or polyphenols were combined to improve the physical and chemical properties of the particles. Additionally, this review analyzes the effect of different protein particle sources on the properties of Pickering emulsions.

Cinnabaris modified with SiO2 nanoparticles stabilized Pickering emulsion to improve the photostability of volatile oil: A Lingzhu San case study

The pharmacological activity of volatile oils (VOs) is significant, but they can generate peroxides under light conditions, reducing the VO content and affecting their stability. This study aims to introduce Pickering emulsion technology to enhance the antioxidant activity of VOs and improve the photostability and efficacy of solid formulations. In this work, Cinnabaris was used as a stabilizer in the formulation of Lingzhu San to prepare Pickering emulsions using high-speed shearing. By controlling the duration of light exposure, the retention rate, degree of oxidation, and changes in volatile components of the volatile oil of Acorus tatarinowii Schott (AT-VO) were compared between the crude oil group and the Pickering emulsion group. Compared with the crude oil group, the Pickering emulsion group significantly improved the retention rate, reduced the degree of oxidation, and mitigated the changes in volatile components. GC–MS analysis of the quantitative and qualitative changes showed that the volatile components of the oil retained by the Pickering emulsion were closer to the untreated AT-VO in the light environment. In addition, the Pickering emulsion with water as the outer phase and oil as the inner phase retarded the formation of peroxides in the VOs and achieved the goal of maintaining the photostability of the VOs.

Pickering Emulsion Properties Generated by Nanofibrillated Cellulose Isolated from Oil Palm Fruit Bunch (OPEFB) as a Stabilizer

This study aims to find the optimal nanofibrillated cellulose (NFC) concentration isolated from oil palm empty fruit bunch (OPEFB) particles to form stable pickering emulsions against creaming and coalescence. The emulsification process is based on a combination of homogenizer and ultrasonication. Pickering emulsion was prepared by mixing the dispersed phase (palm oil) and the dispersing phase (NFC concentration of 0.05 - 0.7 w/v%) at the ratio of 10:90. Fresh emulsion has a milky white appearance and is homogeneous. However, some samples' creaming process occurred on the 30th day of storage. Microscopic observations show that the droplets are round with various sizes. Differences in NFC concentrations significantly affect droplet size, zeta potential, rheology, and emulsion stability. Increasing the NCF concentration resulted in smaller droplet sizes, viscosity, zeta potential, and pickering emulsion stability. The emulsion has high stability against coalescence and creaming. NFC at 0.7 w/v% generates an emulsion with the best characteristics and high stability against creaming and coalescence. OPEFB-based NFC has the potential as a pickering emulsion stabilizer particle that can be applied to the food and non-food industries.

Characteristics of soy protein hydrolysate nanofibrils and their stabilization mechanism for Pickering emulsion: Interfacial properties, Rheology and stability

Enzymatic hydrolysis is an effective method to improve the physicochemical properties of soy protein isolate (SPI) nanofibrils and expand their application in stabilizing Pickering emulsion. In this work, the effects of enzymatic hydrolysis on the SPI fibrillation and the stabilization mechanisms of SPI hydrolysate nanofibrils for Pickering emulsion were investigated. According to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) images and Thioflavin T (ThT) fluorescence data, a higher degree of hydrolysis (DH) contributed to releasing more small molecular weight peptides (mainly from α, α′, and β subunits) to improve apparent rate constant and surface hydrophobicity during fibrillation. When DH increased to 8%, SPI hydrolysate could form long and flexible nanofibrils and possessed the highest content of β-sheet (21.40%), when heated for 12 h. Enzymatic hydrolysis played various positive impacts on the interfacial properties of nanofibrils, including faster interfacial adsorption and near-neutral wettability (92.87°). SPI hydrolysate nanofibrils could impart enhanced gel-like structure and exceptional thermal stability to Pickering emulsions, resulting in a decrease in droplet size from 52.06 μm to 32.74 μm. This work will enhance the exploration of the formation mechanism of nanofibrils and broaden their application in the functional emulsion.

Covalent immobilization of POM-based ILs on magnetic graphene oxide for efficient catalytic oxidative desulfurization of model fuel under solvent-free and moderate reaction conditions

A series of divanado-substituted phosphomolybdic acid-based ionic liquids was successfully prepared and immobilized on the surface of a magnetic graphene oxide (APTES-mGO). The prepared catalysts were characterized and used in oxidative desulfurization (CODS) of model fuel in a solvent-free system. The sample of [C12mim]5PV2Mo10/APTES-mGO, with an alkyl length chain of C12, showed the highest DBT removal percentage, which helped to form a stable Pickering emulsion system. Moreover, the effect of operating conditions, including the reaction time and temperature, catalyst dosage, and O/S molar ratio, on the DBT removal efficiency of the catalyst were investigated employing response surface methodology (RSM). The results showed that the [C12mim]5PV2Mo10/ APTES-mGO was able to completely desulfurize the model fuel under the optimized conditions of 4 g catalyst per liter of the fuel, T = 45 °C, t = 30 min, and O/S = 4. The CODS performance of the catalyst in the presence of other refractory sulfur components (BT and 4,6-DMDBT) was also studied. The designed catalyst could be recovered 8 times without significant losing of its catalytic activity. In addition, 87.15% sulfur removal was achieved for an untreated real diesel sample by adding an extraction step after the CODS processes.

Soy Protein Isolate-Chitosan Nanoparticle-Stabilized Pickering Emulsions: Stability and In Vitro Digestion for DHA.

The purpose of the study was to investigate the stability and oral delivery of DHA-encapsulated Pickering emulsions stabilized by soy protein isolate-chitosan (SPI-CS) nanoparticles (SPI-CS Pickering emulsions) under various conditions and in the simulated gastrointestinal (GIT) model. The stability of DHA was characterized by the retention rate under storage, ionic strength, and thermal conditions. The oral delivery efficiency was characterized by the retention and release rate of DHA in the GIT model and cell viability and uptake in the Caco-2 model. The results showed that the content of DHA was above 90% in various conditions. The retention rate of DHA in Pickering emulsions containing various nanoparticle concentrations (1.5 and 3.5%) decreased to 80%, while passing through the mouth to the stomach, and DHA was released 26% in 1.5% Pickering emulsions, which was faster than that of 3.5% in the small intestine. After digestion, DHA Pickering emulsions proved to be nontoxic and effectively absorbed by cells. These findings helped to develop a novel delivery system for DHA.

Lipase B from Candida antarctica immobilized on amphiphilic Janus halloysite nanosheet and application in biphasic interface conversion

Lipase B from Candida antarctica (CALB) plays a prominent role as a biocatalyst in several industries, especially for biphasic conversion of functional lipids. Herein, an amphiphilic Janus halloysite nanosheet (JHNS) was fabricated and employed simultaneously as a solid surfactant for stabilizing Pickering emulsion and as a carrier for immobilizing CALB, with the aim to realize highly efficient biphasic bioconversion. The obtained JHNS could stabilize Pickering emulsion for at least 7 days. Immobilization of CALB on JHNS improved the substrate affinity, catalytic efficiency, thermal stability, and alkaline tolerance of the enzyme. Moreover, JHNS-based immobilized CALB was exploited as a biocatalytic platform for the conversion of retinyl acetate, with almost twice increase in conversion efficiency. Taken together, the JHNS-based immobilized CALB paves the way for the design of efficient biphasic conversion system for the production of added-value lipids.

Modulation of pea protein isolate nanoparticles by interaction with OSA-corn starch: Enhancing the stability of the constructed Pickering emulsions

The impact of particle concentration (0.5–2.5%) on the stability of Pickering emulsions was investigated in this work. Pickering emulsion was prepared using pea protein isolate (PPI)/octenyl succinic anhydrate corn starch (OSA-CS) composite nanoparticles (PPI/OSA-CS) as stabilizers. PPI/OSA-CS was prepared with pH adjustment and ultrasonic treatment, and the particle size was 100.05 ± 0.46 nm. The formation of PPI/OSA-CS through hydrophobic interaction and hydrogen bond was confirmed by Fourier transform infrared spectroscopy, intrinsic fluorescence spectroscopy and dissociation analysis. The results indicated that the emulsion stabilized with composite nanoparticles at 1.5% particle concentration had smaller particle size and better stability than at other concentrations. This could be attributed to the presence of sufficient composite nanoparticles wrapped around the surface of oil droplets. At high temperature (100 °C) and high ionic strength (500 mM), the emulsion remained stable. These results provide a potential method for preparing a novel and stable Pickering emulsion, which could have important applications in various fields.

The influence of α and α′ subunits on SPI Pickering emulsions based on natural hybrid breeding varieties

In this study, food-grade protein nanoparticles (Wild-NPs, α-lack-NPs, α′-lack-NPs, and (α + α′)-lack-NPs) were organized as emulsion stabilizers via thermal induction. The effects of α and α′ subunits in soybean protein isolate (SPI) on Wild nanoparticle Pickering emulsion (Wild-NPPEs), α-lack nanoparticle Pickering emulsion (α-lack-NPPEs), α′-lack nanoparticle Pickering emulsion (α′-lack-NPPEs) and (α + α′)-lack nanoparticle Pickering emulsion ((α + α′)-lack-NPPEs) were investigated. The Pickering emulsion stabilization mechanism indicated that the α′-lack-NPs particle size, surface hydrophobicity, and contact angle were mostly comparatively large. Therefore, the absence of the α′ subunit made the desorption of protein nanoparticles at the oil and water interface require higher energy. Through the hydrophobic interaction between molecules, the structure and properties of the emulsion were improved, showing good stability. The existence of α′-lack-NPPEs leads to the formation of a gel-like network in the emulsion, which increases the viscosity of the emulsion and makes the network structure of the emulsion more uniform and denser.

Preparation of food-grade EDC/NHS-crosslinked gelatin nanoparticles and their application for Pickering emulsion stabilization

Herein, a safe desolvation and crosslinking method was developed to prepare food-grade bovine bone gelatin (BBG) nanoparticles for Pickering emulsion stabilization. The nanoparticle-like structures were formed by adjusting pH 9.0 and adding ethanol, and then stable nanoparticles were formed by using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) as crosslinker. Compared with other pH (2.5, 5.0, 7.0, and 12.0), pH 9.0 was the appropriate pH to prepare BBG nanoparticles. Individual nanoparticles (6.50 nm in height), oligomeric nanoparticles (13.42–22.52 nm in height), and polymeric nanoparticles (obvious liquid-precipitate separation) were formed at EDC·HCl/NHS concentrations of 6, 9–12, and 15–20 mg/mL, respectively. The oligomeric nanoparticles induced the highest emulsion creaming stability. The emulsion creaming ability increased with the increase of BBG nanoparticle concentrations. Low NaCl concentration (e.g., 100 mmol/L) could increase the emulsion creaming stability. Finally, 4 °C was the best storage temperature for fish oil-loaded Pickering emulsions.

PH and redox dual-responsive Pickering emulsion based on silica nanoparticles and novel ferrocene surfactant

Responsive Pickering emulsions capable of responding to external stimuli have been extensively studied, however, there are few studies on double-responsive Pickering emulsions. Here in, a novel ferrocene surfactant (FcACUa) was synthesized and combined with aminated silica nanoparticles (0.5 wt%) to stabilize pH and redox sensitive smart Pickering emulsions. The carboxyl groups act as pH-sensitive parts, while ferrocene serves as the redox-responsive center. Stability and pH/redox response performance of the emulsions were investigated through various methods, such as the contact angle, macroscopic states, creaming index, microscopic images, droplet size distributions, etc. All atom molecular dynamics and dissipative particle dynamics simulations were used to probe the distribution of nanoparticles and surfactant at the water-oil interface, as well as to reveal the stabilization and pH/redox response mechanisms of the Pickering emulsions. Pickering emulsions can be reversibly switched between stable and unstable by adding HCl and NaOH or adding H2O2 and N2H4·H2O. After five pH-induced cycles, the emulsion shows no significant degradation or morphological changes. However, for the redox induced emulsification demulsification process, the size of the emulsion drops increases with the increase of the number of cycles. This work provides insights into the Pickering emulsion stabilization mechanism and the regulation mechanisms of pH and redox stimulation, which may have potential value in emulsion polymerization, biphasic catalysis, and oil and gas transportation.

Cinnamon essential oil Pickering emulsions: Stabilization by bacterial cellulose nanofibrils and applications for active packaging films

Pickering emulsions are emulsions stabilized by solid particles with a wide range of potential applications as they typically provide more stable systems than surface-stabilized emulsions. Among the various solid stabilizers, bacterial cellulose (BC) may open up new opportunities for future Pickering emulsions due to its unique nano-size, amphiphilicity and other excellent properties. In this study, BC, TEMPO-oxidized BC (TOBC) and dialdehyde cellulose (DAC) were used as emulsifiers to stabilize cinnamon essential oil (CEO) Pickering emulsions. The microstructure, oil droplet size distribution, storage and loss moduli of the Pickering emulsions were affected by the type of emulsifier used. Compared to BC and DAC nanofibers, TOBC nanofibers exhibited better emulsifying capacity. TOBC (1%)-stabilized Pickering emulsion showed smaller droplet size, narrower size distributions, better stability and sustained release ability. Moreover, the Pickering emulsions showed high antibacterial activities against Gram-positive bacteria S. aureus and Gram-negative bacteria E. coli. Active gelatin composite films containing TOBC (1%)-stabilized CEO Pickering emulsions were successfully fabricated and showed good antibacterial and antioxidant properties, which make them suitable for food packaging application.

Pickering emulsions stabilized by moringa seed protein: Regulating the emulsion properties by adjusting the Maillard reaction

Due to its high hydrophobicity and low solubility, the unmodified moringa seed protein (MSP) is not ideal for creating a stable Pickering emulsion. Therefore, preparing MSP nanoparticles with adjustable surface properties and clarifying their surface properties are of immense significance to expand the application of MSP in the emulsion. In this study, MSP was employed as a starting material to prepare moringa seed protein-chitosan nanoparticles (MSP-CS/NPs) by Maillard reaction. The nanoparticles were then used to stabilize the Pickering emulsion. The structural properties of the copolymers were modulated by controlling the protein-to-polysaccharide ratio. It was found that when the volume ratio of MSP to CS was 4:1, the emulsification performance was the best, and the antioxidant performance of the Pickering emulsion was the strongest. Pickering emulsion showed good antibacterial properties when loaded with Mupirocin. Overall, this work demonstrates the potential application of the Moringa seed protein-chitosan complex in stabilizing Pickering emulsions and provides a theoretical foundation for the development of functional Pickering emulsions.

Regenerated silk fibroin for the stabilization of fish oil-loaded Pickering emulsions

Protein nanofibril-stabilized Pickering emulsion is a promising emulsion in the field of food emulsion. However, no microscale protein fibrils have been applied as emulsifiers for the stabilization of food emulsions. In this work, regenerated silk fibroin (RSF) was prepared and applied to stabilize fish oil-loaded Pickering emulsions. RSF could form a microfiber-microfiber-nanofilm interconnection network at the oil/water interfaces to stabilize the emulsions. Fish oil-loaded RSF-stabilized Pickering emulsions showed low creaming (0% ≤ creaming index < 10%) during the 31-day storage at room temperature, which was lower than the creaming index values (10–47%) of the emulsions in previous report. Moreover, RSF is an excellent emulsifier to prepare semigel and gel of fish oil-loaded RSF-stabilized Pickering emulsions. For the RSF-stabilized Pickering emulsions, a lower oil/water volume ratio might induce lower initial droplet size, slower droplet coalescence, slower liquid-gel transition, and lower creaming stability. In addition, higher homogenization energy input (speed and time) and RSF concentration might induce lower initial droplet size, slower droplet coalescence, faster liquid-gel transition, and higher creaming stability for Pickering emulsions. Therefore, RSF could have good emulsion stabilization ability by adjusting preparation parameters and is a promising emulsifier to prepare emulsion semigel and gel in the field of food emulsions. This work provided useful information to understand the effects of preparation parameters on the formation and stability of RSF-stabilized emulsions.

Preparation, Characterization, and Utilization of Crosslinked and Dual‐Modified Banana Starch for Stabilizing Pickering Emulsion

AbstractThe effect of sodium trimetaphosphate (STMP, 1%–3%), STMP + dry heat (STMP‐DH, at 180 °C for 60 min), and octenyl succinic anhydride (OSA, 3%) on functional, structural, morphological, and thermo‐rheological properties of banana starch is studied. Similar Fourier‐transform infrared (FTIR) and X‐ray diffraction (XRD) patterns of modified starches indicate minor structural changes; however, the degree of crystallinity significantly of native starch (26.88%) reduces after crosslinking (16.32%) and dual modification (13.91%). The native granules are flattened, elongated, oval‐ellipsoidal, and compact granules, whereas STMP starches have smoother surfaces than STMP‐DH starches. Due to changes in structure and functional groups, swelling and solubility of granules decrease, which depreciate the viscosity curve during cooking. In addition, pasting temperature elevates after STMP modification (76.3–83.1 °C) and remains comparable after STMP‐DH (76.3–75.1 °C). The rheological analysis shows that native starch gel has more shear‐thinning behavior and dominant elastic component than modified starches. The modified edible starch particles are successfully used to stabilize oil‐in‐water Pickering emulsion. The 2% and 3% STMP starches show better storage stability comparable to 3% OSA starch for up to 30 days. However, the loss in functional groups and amphiphilic properties of STMP‐DH results in creaming and an inability to perform as desired.

Cellulose Nanofibril Stabilized Pickering Emulsion Templated Aerogel with High Oil Absorption Capacity.

Nanocellulose-based aerogels, featuring a three-dimensional porous structure, are considered as a desirable green absorbent because of their exceptional absorption performance as well as the abundance and renewability of the raw material. However, these aerogels often require hydrophobic modification or carbonization, which is often environmentally harmful and energy-intensive. In this study, we introduce a Pickering-emulsion-templating approach to fabricate a cellulose nanofibril (CNF) aerogel with a hierarchical pore structure, allowing for high oil absorption capacity. n-Hexane-CNF oil-in-water Pickering emulsions are prepared as an emulsion template, which is further lyophilized to create a hollow microcapsule-based CNF (HM-CNF) aerogel with a density ranging from 1.3 to 6.1 mg/cm3 and a porosity of ≥99.6%. Scanning electron microscopy and Brunauer-Emmett-Teller analyses reveal the HM-CNF aerogel's hierarchical pore structure, originating from the CNF Pickering emulsion template, and also confirm the aerogel's very high surface area of 216.6 m2/g with an average pore diameter of 8.6 nm. Furthermore, the aerogel exhibits a maximum absorption capacity of 354 g/g and 166 g/g for chloroform and n-hexadecane, respectively, without requiring any surface modification or chemical treatment. These combined findings highlight the potential of the Pickering-emulsion-templated CNF aerogel as an environmentally sustainable and high-performance oil absorbent.