Soy glycinin as food-grade Pickering stabilizers: Part. II. Improvement of emulsification and interfacial adsorption by electrostatic screening

Impact of NaCl perturbation on physicochemical and structural properties of preheat-treated egg white protein modulating foaming property

This study aimed to investigate the mechanism of NaCl perturbed preheat-treated egg white proteins' (EWPs) physicochemical and structural properties to modulate the foaming property (FP). The results revealed that NaCl regulated the salinolysis (5 mM) - salt precipitation (50 mM) - gradual or complete coverage with hydrated Na+ of the hydration layer (100-300 mM) - enhanced Cl- hydration repulsion (500 mM) of EWP, showing a gradual decrease in aggregates particle size, and reversibility of structural freedom, including moleculer flexibility and surface hydrophobicity. Whereas preheating temperature affected the secondary structure rearrangement and tertiary conformation exposure, and excessive temperature reduced foaming capacity while enhanced foam stability, with a tight correlation between NaCl-mediated EWPs' FP and the extent of Na+ covering the hydration layer. The findings provide a theoretical basis for processing factors to modulate the protein hydration layer to influence the functional properties.

Cholic Acid/Glutathione-Assembled Nanofibrils for Stabilizing Pickering Emulsion Biogels

Achieving the delicate balance required for both emulsion and gel characteristics, while also imparting biological functionality in gelled emulsions, poses a significant challenge. Herein, we report on Pickering emulsion biogels formed by novel biological nanofibrils assembled from natural glutathione (GSH) and a tripod cholic acid derivative (TCA) via electrostatic interactions. GSH, composed of tripeptides with carboxyl groups, facilitates the protonation and dissolution of TCA compounds in water and the electrostatic interactions between GSH and TCA trigger nanofibrillar assembly. Fibrous nuclei initially emerge, and the formed mature nanofibrils can generate a stable hydrogel at a low solid concentration. These nanofibrils exhibit efficient emulsifying capability, enabling the preparation of stable Pickering oil-in-water (O/W) emulsion gels with adjustable phase volume ratios. The entangled nanofibrils adsorbed at the oil-water interface restrict droplet movement, imparting viscoelasticity and injectability to the emulsions. Remarkably, the biocompatible nanofibrils and stabilized emulsion gels demonstrate promising scavenging properties against reactive oxygen species (ROS). This strategy may open new scenarios for the design of advanced emulsion gel materials using natural precursors and affordable building blocks for biomedical applications.

Pickering emulsion stabilized by grass carp myofibrillar protein via one-step: Study on microstructure, processing stability and stabilization mechanism

In this study, edible Pickering emulsions stabilized with GMP particles were prepared for the first time using low-value grass carp myofibrillar protein (GMP). To elucidate the emulsion formation mechanism, the grass carp myofibrillar protein particles were first characterized, and the results showed that the lyophilized GMP particles had an irregular polyhedral structure and were amphiphilic nanoparticles. The stability of GMP-based emulsions tended to stabilize with the increase of GMP concentration at an appropriate oil-to-water volume ratio, with a decrease in droplet particle size and an increase in water-holding capacity, storage stability, and rheological stability, whereas the phenomenon of droplet aggregation after storage appeared at 4.0% additive level. Therefore, appropriate concentrations of GMP at a certain oil-to-water volume ratio can stabilize Pickering emulsions, which have an important future as a potential food-grade active substance delivery carrier for biological applications.

Fabrication, characterization and application of Pickering emulsion gels stabilized by defatted grape seed powder

The feasibility of defatted grape seed powder (DGSP) stabilizing Pickering emulsion gels as butter substitute was investigated. The Pickering emulsion gel was constructed using DGSP through high-speed homogenization, and the effects of particle concentration (c) and oil-phase (Medium chain triglyceride) volume fraction (φ) on its structure and properties were investigated. Its application as a butter substitute was also evaluated. The results showed that DGSP had various particle shapes, a wide particle size distribution (3-130 μm), and a three-phase contact angle of 128.9 ± 2.3°. The O/W Pickering emulsion gels with φ ≥ 60% could be obtained at c ≥ 2%. The droplet diameter was negatively correlated with c and positively correlated with φ, while the gel strength was positively related to c and φ. The resulting emulsion gel demonstrated solid-like viscoelastic behavior and pseudoplasticity, and had the potential to serve as a butter substitute. The results can promote the application of grape seeds in food.

Influence of thermal denaturation on whey protein isolates in combination with chitosan for fabricating Pickering emulsions: a comparison study

Composite natural emulsifiers such as whey protein isolate (WPI) and chitosan (CS) are commonly used in Pickering emulsions to address the effect of thermal deformation of proteins before complexation with CS and heating after complexation. In this study, the properties of WPI and CS composites were investigated by complexing CS with either unmodified WPI or thermally denatured WPI (DWPI). Three types of composite particles were prepared, WPI-CS, DWPI-CS, and D(WPI-CS). Atomic force microscopy revealed that the composite particles formed larger aggregates with increased contour size and surface roughness compared to CS and WPI, whereas the interfacial tension decreased, indicating improved emulsifying abilities. Fourier-transform infrared analysis revealed differences in the hydrogen bonds between CS and WPI/DWPI. All three composite particles formed stable emulsions with droplet sizes of 20.00 ± 0.15, 27.80 ± 0.35, and 16.77 ± 0.51 μm, respectively. Thermal stability experiments revealed that the curcumin emulsion stabilized with WPI-CS and DWPI-CS exhibited relatively better thermal stability than that stabilized with D(WPI-CS). In vitro experiments results indicated that the bioaccessibility of the curcumin emulsion stabilized with WPI-CS was 61.18 ± 0.16%, significantly higher than that of the emulsions prepared with the other two composite particles (p < 0.05). This study will enable the customized design of WPI composite-based Pickering emulsions for application in the food and nutrition industries.

Insight into oil-water interfacial adsorption of protein particles towards regulating Pickering emulsions: A review

Over the past decade, Pickering emulsions (PEs) stabilized by protein particles have been the focus of researches. The characteristics of protein particles at the oil-water interface are crucial for stabilizing PEs. The unique adsorption behaviors of protein particles and various modification methods enable oil-water interface to exhibit controllable regulation strategies. However, from the perspective of the interface, studies on the regulation of PEs by the adsorption behaviors of protein particles at oil-water interface are limited. Therefore, this review provides an in-depth study on oil-water interfacial adsorption of protein particles and their regulation on PEs. Specifically, the formation of interfacial layer and effects of their interfacial characteristics on PEs stabilized by protein particles are elaborated. Particularly, complicated behaviors, including adsorption, arrangement and deformation of protein particles at the oil-water interface are the premise of affecting the formation of interfacial layer. Moreover, the particle size, surface charge, shape and wettability greatly affect interfacial adsorption behaviors of protein particles. Importantly, stabilities of protein particles-based PEs also depend on properties of interfacial layers, including interfacial layer thickness and interfacial rheology. This review provides useful insights for the development of PEs stabilized by protein particles based on interfacial design.

Freeze-thaw stability of Pickering emulsion stabilized by modified soy protein particles and its application in plant-based ice cream

Pickering emulsions are of great interest to the food industry and their freeze-thaw stability important when used in frozen foods. Particles of soybean isolate (SPI) were heat treated and then crosslinked with transglutaminase (TG) enzyme to produce Pickering emulsions. The protein particles produced using unheated and uncrosslinked SPI (NSPI) was used as the benchmark. The mean particle size, absolute zeta potential, and surface hydrophobicity of protein particles produced using heat treatment and TG crosslinking (at 40 U/g) SPI (HSPI-TG-40) were the highest and substantially higher than those produced using NSPI. The thermal treatment of protein particles followed by crosslinking with TG enzyme improved the freeze-thaw stability of Pickering emulsions stabilized by them. The Pickering emulsions produced using HSPI-TG-40 had the lowest temperature for ice crystal formation and they had better freeze-thaw stability. The plant-based ice cream prepared by HSPI-TG-40 particle-stabilized Pickering emulsions had suitable texture and freeze-thaw stability compared to the ice cream produced using NSPI. The Pickering particles produced using heat treatment of SPI followed by crosslinking with TG (at 40 U/g) produced the most freeze-thaw stable Pickering emulsions. These Pickering particles and Pickering emulsions could be used in frozen foods such as ice cream.

Structural properties of Phoenix oolong tea polysaccharide conjugates and the interfacial stability in nanoemulsions

BACKGROUND

Tea polysaccharide conjugate (TPC) is a naturally occurring active substance that is extracted from tea. Owing to its benefits in enhancing human immunity and antioxidant effects, TPC is widely used in culinary products. The binding mode of polysaccharides and proteins in TPC, however, has not been well studied; it may be closely related to their functional properties, especially emulsification.

RESULTS

The molecular weights and monosaccharide compositions of TPC were determined by ion chromatography and high-performance gel permeation chromatography. Although the functional groups of polysaccharides and proteins were confirmed by infrared spectroscopy, the presence of proteins could not be detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis and ultraviolet spectroscopy. It was hypothesized that the hydrophobic groups of the proteins in TPC were wrapped by polysaccharide chains, thus making the proteins undetectable. The rheology and interfacial protein adsorption results show that TPC forms a viscoelastic film at the oil-water interface to prevent the aggregation of oil droplets, thereby enhancing the stability of the emulsion. Based on these structural and emulsifying properties of TPC, the binding mode of polysaccharides and proteins along with their phase behavior at the oil-water interface of the emulsion was speculated.

CONCLUSION

In TPC, the hydrophilic groups of the proteins are linked to polysaccharides by covalent interactions, where the hydrophobic groups are wrapped with the polysaccharide chains with the help of hydrophobic forces to form a hydrophobic core. The unique binding of polysaccharides and proteins in TPC enhances its amphiphilic properties, which can be effectively distributed at the oil-water interface and form stable emulsions. © 2023 Society of Chemical Industry.

The preparation of Diacylglycerol-rich soybean oil by acetylated modification of arachin nanoparticles for W/O Pickering emulsion system

Pickering emulsion catalytic system (PEC) stabilized by nanoparticles is an efficient catalytic platform. Herein, a high-performance PEC was constructed by acetylated modification of arachin nanoparticles (AAPs). The results showed the pI of arachin was decreased from pH 5.5 to pH 3.5. The surface hydrophobicity index was significantly increased (from 56.28 ± 4.23 to 120.77 ± 0.79) after acetylated modification. The three-phase contact angle of AAPs was 91.20 ± 0.98°. AAPs were used as lipase immobilization carriers to increase the activity of free lipase fabricating lipase-AAPs. The immobilization efficiency and activity of lipase-AAPs were 12.95 ± 0.03% and 1.74 ± 0.07 U/mg, respectively. Enzymatic reaction kinetics showed that V_m of lipase-AAPs was twice of free lipase. K_m was 1/5 of free lipase. The catalytic efficiency of PEC to prepare DAG was 2.36 times of biphasic catalytic system (BCS). This work provided a promising way to promote the efficiency of DAG preparation.

Stability of protein particle based Pickering emulsions in various environments: review on strategies to inhibit coalescence and oxidation

The emerging research interests in fabrication of protein particles as soft-particle emulsifiers show the prospective potential of using protein particles in novel poly-phase dispersing food systems. This review first provides a comprehensive summary and analysis on the dominant role of key physicochemical properties of protein particles including wettability, morphology, surface charge and protein concentration on their emulsifying abilities to construct Pickering emulsions. It was found that the constructed emulsions showed high sensitivity to changes in pH, ionic strength and temperature (thermal and freeze-thaw treatment). Moreover, oxidation remains as a challenge for protein particle based Pickering emulsions during prolonged storage, reducing their acceptance in food products. Current strategies for improving the stability of these emulsions to variable aqueous conditions and variable temperatures, and restricting oxidation event are summarized. In summary, an "ideal" protein particle-based Pickering emulsion system is proposed, encompassing aspects of interfacial property, emulsion network and texture, and antioxidant enrichment, thus promoting industrial translation into novel food and nutraceutical products.

Thermomechanically micronized sugar beet pulp: Emulsification performance and the contribution of soluble elements and insoluble fibrous particles

In this work, thermomechanically micronized sugar beet pulp (MSBP), a micron-scaled plant-based byproduct comprised of soluble elements (∼40 wt%) and insoluble fibrous particles (IFPs, ∼60 wt%), was used as a sole stabilizer for oil-in-water emulsion fabrication. The influence of emulsification parameters on the emulsifying properties of MSBP was investigated, including emulsification techniques, MSBP concentration, and oil weight fraction. High-speed shearing (M1), ultrasonication (M2), and microfludization (M3) were used to fabricate oil-in-water emulsions (20% oil) with 0.60 wt% MSBP as stabilizer, in which the d_4,3 value was 68.3, 31.5, and 18.2 μm, respectively. Emulsions fabricated by M2 and M3 (higher energy input) were more stable than M1 (lower energy input) during long-term storage (30 days) as no significant increase of d_4,3. As compared to M1, the adsorption ratio of IFPs and protein was increased from ∼0.46 and ∼0.34 to ∼0.88 and ∼0.55 by M3. Fabricated by M3, the creaming behavior of emulsions was completely inhibited with 1.00 wt% MSBP (20% oil) and 40% oil (0.60 wt% MSBP), showing a flocculated state and could be disturbed by sodium dodecyl sulfate. The gel-like network formed by IFPs could be strengthened after storage as both viscosity and module were significantly increased. During emulsification, the co-stabilization effect of the soluble elements and IFPs enabled a compact and hybrid coverage onto the droplet surface, which acted as a physical barrier to endow the emulsion with robust steric repulsion. Altogether, these findings suggested the feasibility of using plant-based byproducts as oil-in-water emulsion stabilizers.

Fabrication of Antioxidant Pickering Emulsion Based on Resveratrol-Grafted Zein Conjugates: Enhancing the Physical and Oxidative Stability

Lipid oxidation is still a major problem complicating the development of food emulsions. In this study, an antioxidant Pickering emulsion stabilized by resveratrol-grafted zein (Z-R) conjugates and pectin (P) complex particles was prepared. The hydrophilic pectin successfully adjusted the wettability of Z-R; when the mass ratio of Z-R to P was 2:1 (Z-R/P2:1), the three-phase contact angle was 90.68°, and the wettability of the particles was close to neutral. Rheological analysis showed that the emulsion formed an elastic gel structure. FTIR spectra indicated that there was a hydrogen bond and electrostatic interaction between Z-R and P. The disappearance of characteristic infrared peaks of corn oil was due to a dense protective film formed on the surface of oil drops by Z-R/P2:1 particles, which was confirmed by confocal laser scanning microscopy. The emulsion stabilized by Z-R/P2:1 had excellent physical stability at a wide range of pH values (4-9), salt ion concentrations (0.04-0.15 mol·L-1) and storage times (0-30 days). The anti-lipid oxidation ability of the emulsion was outstanding; after storage for 14 days at room temperature, the MDA content in the emulsion was only 123.85 μmol/kg oil. In conclusion, the Z-R/P2:1 particles prepared in this study can effectively stabilize a Pickering emulsion and expand the usability of the method for constructing antioxidant Pickering emulsions.

Storage stability and in vitro digestion of apigenin encapsulated in Pickering emulsions stabilized by whey protein isolate–chitosan complexes

Few studies have investigated the encapsulation of apigenin in solid particle-stabilized emulsions. In this work, Pickering emulsions containing apigenin and stabilized by whey protein isolate-chitosan (WPI-CS) complexes were created to enhance the bioavailability of apigenin. Different lipids including medium-chain triglycerides (MCTs), ethyl oleate (EO), and corn oil (CO) were selected to fabricate lipid-based delivery systems. The microstructure of the Pickering emulsions, as revealed by optical and cryo-scanning electron microscopies, showed that the oil droplets were dispersed evenly and trapped by a three-dimensional network formed by the WPI-CS complexes, which was further confirmed by rheology properties. After 30 days of storage, Pickering emulsions with MCTs achieved the highest apigenin retention rate, exhibiting 95.05 ± 1.45% retention when stored under 4°C. In vitro gastrointestinal tract experiments indicated that the lipid types of the emulsions also affected the lipid digestion and release rate of apigenin. Pickering emulsions with MCTs achieved a higher bioaccessibility compared to that of the other two emulsions (p < 0.01). These results indicate that the delivery system of Pickering emulsions with MCTs stabilized by WPI-CS complexes offers good storage stability and improved bioaccessibility of apigenin.

Evaluation of Emulsifying Ability of Phospholipids by Langmuir Monolayers and Stability of High Oil Ratio O/W Emulsions

High oil ratio fat emulsion injections are prone to poor emulsification, rapid creaming, and other quality problems; therefore, the selection of emulsifiers with high emulsifying ability is crucial for the production of fat emulsions. The existing methods used to evaluate the emulsifying ability of emulsifier are to evaluate the emulsifying ability from the emulsifier itself. In the study, Langmuir monolayer selected the most miscible phospholipid with oil phase from the alternative three phospholipids by studying the molecular interaction between oil phase and phospholipid at the air/water interface. The miscibility and thermodynamic stability analyses of the different oil phase/phospholipid mixed monolayers were performed, and the data from [Formula: see text] and [Formula: see text] concluded that all three oil phases had the strongest molecular interaction with E80 and the best miscibility. The emulsions were then prepared and analyzed by the results of particle size, ζ-potential, and stability of the emulsions, where the surface free energy in the stability test echoed the results reflected by the [Formula: see text] values in the thermodynamic stability test. These results indicate that Langmuir monolayers can be used to study the interaction between oil phase and emulsifier, thus providing new ideas for evaluating the emulsifying ability of phospholipids.

NaCl induces flocculation and lipid oxidation of soybean oil body emulsions recovered by neutral aqueous extraction

BACKGROUND

Soybean oil bodies (SOB) are naturally pre-emulsified lipid droplets recovered directly from soybean seeds. Almost all food emulsions contain salts. However, it was not clear how the incorporation of salts affected the physicochemical stability of SOB.

RESULTS

This study investigated the effect of NaCl (0-1.2%) on the physical and oxidative stability of SOB emulsions under neutral (pH 7) and acidic (pH 3) conditions. In the presence of NaCl, the SOB emulsion (pH 7) showed strong flocculation during storage due to electrostatic screening. The NaCl-induced flocculation of SOB was attenuated at pH 3, which may be due to the difference in conformation or interaction of the protein interfaces covering SOB at different pH values. The increase in ionic strength or acid conditioning treatment resulted in a remarkable increase in the stability of SOB emulsions against coalescence. The confocal laser scanning microscopy images also confirmed the NaCl-induced changes in the flocculation/coalescence properties of SOB. The oxidative behavior tests indicated that SOB emulsions containing NaCl were more susceptible to lipid oxidation but protein oxidation was inhibited due to electrostatic screening, which reduced pro-oxidant accessibility of unadsorbed proteins in the emulsion. This oxidative behavior was attenuated at pH 3.

CONCLUSION

The incorporation of NaCl significantly reduced the physical and oxidative stability of the SOB emulsion, and acidic pH mitigated NaCl-induced flocculation and lipid oxidation of SOB. © 2021 Society of Chemical Industry.

Emulsifying capacity of peanut polysaccharide: Improving interfacial property through the co-dissolution of protein during extraction

The co-dissolution of residual protein from byproduct (PPSI) was employed to improve the interfacial property of peanut polysaccharide (PPS). Protein content in the PPSI and PPS were 16.89% and 2.58%, respectively. The convent bonding and intermolecular interaction maintained the complex structure in PPSI. More protein promoted the shift from linear chain conformation to spherical particle, weakened surface charge, induced stronger intermolecular attraction and wettability, which facilitated interfacial adsorption of PPSI. Concomitantly, the linear chain after adsorbing the O/W interface was observed in PPSI-polystyrene, promoting the cross-linking between adsorption layers and thereby forming the elastic interfacial film. Consequently, the emulsion borne smaller size. Subsequently, the particles in continuous phase moved to the adsorption layer via intermolecular interaction and then formed a gel, enhancing stability against oil coalescence, the thermal and refrigerated treatments. Additionally, the acidified (pH 3.0) PPSI further strengthened the emulsion structure and improved its creaming and freeze-thaw stability.

Enhancing bioaccessibility and bioavailability of carotenoids using emulsion-based delivery systems

The consumption of foods rich in antioxidants, vitamins, minerals including carotenoids etc. can boost the immune system to help fight off various infections including SARS- CoV 2 and other viruses. Carotenoids have been gaining attention particularly in food and pharmaceutical industries owing to their diverse functions including their role as pro-vitamin A activity, potent antioxidant properties, and quenching of reactive oxygen (ROS), such as singlet oxygen and lipid peroxides within the lipid bilayer of the cell membrane. Nevertheless, carotenoids being lipophilic, have poor solubility in aqueous medium and are also chemically instable. They are susceptible to degrade under stimuli environmental conditions during food processing, storage and gastrointestinal passage. They also exhibit poor oral bioavailability, thus, their applications in aqueous-based foods are limited. As a consequent, suitable delivery systems including colloids-based are needed to enhance the solubility, stability and bioavailability of carotenoids. This review presents challenges of incorporation and delivery of carotenoids focusing on stability and factors affecting bioavailability. Furthermore, designed factors impacting bioaccessibility and bioavailability of carotenoids using emulsion-based delivery systems are explicitly explained. Each delivery system exhibits its own advantages and disadvantages; thus, the delivery systems should be designed based on their targets and their further applications.

Protein isolate from Stauntonia brachyanthera seed: Chemical characterization, functional properties, and emulsifying performance after heat treatment

The seed of Stauntonia brachyanthera is usually regarded as waste after fructus processing. Here, the potential utilization value of the protein isolate (SSPI) from seeds was evaluated by investigating its physicochemical and functional properties. SSPI was a complex protein containing 7 distinct subunits that had high contents of most essential amino acids. The maximum foaming capacity of SSPI was 406.7 ± 41% at pH 9.0, and the water holding/oil adsorption capacities were 4.66 g/g and 9.06 g/g, respectively. SSPI aggregates with a particle size of 154.1 ± 5.2 nm was prepared after heat treatment, which was performed as a Pickering-like stabilizer for the structuring of water-in-oil-in-water emulsions. The outer droplet size of emulsions decreased as the aggregate concentration increased. Emulsion gels could be observed with the increasing aggregate concentration and oil fraction. Further study found that the stabilities of inner water-in-oil droplets and creaming were progressively increased by increasing the aggregate concentration during storage.

Citrus fiber for the stabilization of O/W emulsion through combination of Pickering effect and fiber-based network

In this study, oil-in-water emulsions stabilized by citrus fiber were prepared and characterized. We found that citrus fiber can produce stable gel-like, surfactant-free O/W emulsions with microscale droplet sizes at fiber concentrations upon 2% (W/V) using 25% (V/V) oil. The interfacial framework, citrus fiber partition between the continuous phase and state of the droplets of emulsions were visualized by confocal laser scanning microscopy (CLSM), confirming that in addition to Pickering stabilization, the citrus fiber-based network also contributed to stabilization of the emulsions. The citrus fiber-stabilized emulsion is typical non-Newtonian fluid and its interfacial viscosity is not influenced obviously by changing pH from 2 to 10, ionic strength of NaCl from 0.00 to 1.00 mol/L or temperature from -20 to 70 °C. The acquired findings in this study show that citrus fiber can fabricate Pickering emulsions with excellent stability and solve the problem of resource waste during the pectin produce process.

Characterization and analysis of an oil-in-water emulsion stabilized by rapeseed protein isolate under pH and ionic stress

BACKGROUND

Presently, identifying natural compounds as emulsifiers is a popular topic in the food industry. Rapeseed protein isolate (RPI) is a natural plant protein with excellent emulsifying properties, but it has not been systematically developed and utilized.

RESULTS

This study investigated the surface hydrophobicity, wettability, and protein solubility of RPI to further explain its emulsifying behavior in emulsion systems. Nanoemulsions stabilized by RPI at varying protein concentration, pH, and ionic strength were prepared. The size distribution, zeta potential, flocculation index, creaming index, microstructure, rheology, and protein secondary structure of emulsions were measured. The emulsion stabilized by 20 g L^-1 RPI at pH 10.0, 200 mmol L^-1 ionic strength revealed an appropriate droplet size of 555 nm and the most internal gel strength without creaming phenomenon. Circular dichroism spectroscopy showed a positive correlation between emulsion stability and α-helix ratio, indicating the environment factors affected emulsion stability by acting on its hydrogen bonds.

CONCLUSIONS

This study demonstrates that RPI is a practical emulsifier for stabilizing nanoemulsions. About 20 g L^-1 RPI can stabilize 100 mL L^-1 oil in water; stable emulsions can be formed at most pH conditions (except 7.0); ion addition will aggravate the emulsion flocculation, but also increase the internal gel strength. © 2020 Society of Chemical Industry.