A new insight into the influence of pH on the adsorption at oil-water interface and emulsion stability of egg yolk protein

Disturbing egg yolk protein structure via pH-shifting treatment for interface reorganization: Improving solubility to enhance oil-water interface adsorption and emulsification properties

This study explored the impact of varying alkalinity levels in pH-shifting treatments on egg yolk protein (EYP) emulsification and investigated the underlying oil-water interface adsorption mechanism. Increasing alkaline pH-shifting treatment exposed more hydrophobic groups within EYP, altering its tertiary structure. Moreover, pH-shifting treatment reduced solution particle size (P < 0.05), possibly by disintegrating insoluble egg yolk granules (EYG) into smaller subunits. Under pH 12.0-shifting conditions, egg yolk (EY) solution reached minimum turbidity and maximum solubility (81.62 %). During initial adsorption, pH 9.0-shifting solution exhibited maximum diffusion rate (0.049 mN/m/s), correlated with minimum solution particle size (88.36 nm). Subsequently, alkaline pH-shifting induced protein rearrangement at the oil-water interface, leading to maximum interfacial pressure (21.01 mN/m) and viscoelastic modulus (44.55 mN/m) under pH 12.0-shifting conditions. This increased emulsion stability by 23.82 % with the lowest creaming index (21.82 %). These findings were crucial for enhancing EYP utilization and promoting EY as a food emulsifier.

Exploring the influence of different enzymes on soy hull polysaccharide emulsion stabilization: A study on interfacial behavior and structural changes

The interfacial behavior of soy hull polysaccharide (SHP) at the oil-water interface and the stabilization mechanism of high internal phase emulsion (HIPE) with three enzymes (α-amylase, trypsin and papain) were investigated. The diameter of the α-amylase-treated emulsion was the minimum at 40 min, indicating that the carbohydrate portions of SHP form a thick layer on the surface of the droplet to prevent aggregation. Moreover, Raman spectroscopy revealed significantly higher levels of disordered content of SHP emulsion treated with α-amylase at 60 min, potentially affecting the directional movement of SHP molecules in the emulsion. Conversely, the content of β-sheet and β-turn was lower than trypsin and papain, possibly due to ion-dipole interaction between the polar group residues within SHP and ions, or protonation with H+.

Effects of pasteurization temperature and amino acids on the gelation behavior of liquid egg yolk: Emphasizing rheology, gel properties, intermolecular forces and microstructure

Pipeline blockage caused by liquid egg yolk (LEY) in the pasteurization process has become an urgent problem for egg industry. This study investigated the effects of amino acids (betaine/proline) on rheology of LEY and gel property of egg yolk gel (EYG) at various pasteurization temperatures (68, 72, and 76 °C). Rheological results revealed that 72 °C was the key transition point for increase in LEY thermal aggregation rate. Average particle size of EYG, BEYG and PEYG increased by 63.9 %, 27.3 % and 17.3 % with increasing pasteurization temperature. Amino acids promoted increase in disulfide bonding content and facilitated retention of free and bound water within gels. Moreover, amino acids enhanced crystallinity and order of gel structures. Amino acids can effectively mitigate thermal aggregation of LEY at mild temperatures and promote cross-linking of gel network at high temperatures. This study provides a theoretical foundation for heat resistance of LEY and application of EYG.

Improved toughening attributes of coix seed oil high internal phase Pickering emulsion gel via the carrageenan and super-deamidated wheat gluten microparticles interfacial network fotified by the acid-heat induction strategy

The toughening coix seed oil (CSO) high internal phase Pickering emulsion (CSO-HIPES) and gel (CSO-HIPESG) comprised of carrageenan (CR)/super-deamidated-gluten (SDG) micro-particles (CR/SDG) were investigated via acid-heat induction. Results showed polysaccharide natural deep eutectic solvent (P-NADES) by citric acid-glucose-carrageenan ((CGCR), molar ratio at 1:1:0.035) was the crucial for the preparation of SDG (deamidation degree, 99.38 %). P-NADES super-deamidation significantly enhanced emulsifying properties of SDG, increased the exposure of cysteine residues (26.77 μM/g) and strengthened hydrogen bonding interactions between SDG protein molecules. Confocal laser scanning microscope displayed the embedded CSO formed uniformly distributed emulsion droplets of smaller size (from 1253.97 to 253.35 nm) along with increased electrostatic repulsion (from 8.72 to 21.03 mV) of CSO-HIPES. It had excellent interfacial stability for the storage of 90 d under the optimized conditions at pH 5. CSO-HIPESG displayed exceptional stability towards heat (70-78 °C, 20-40 min), NaCl (20-40 mol/L), storage (90 d) upon acid-heat induction of CSO-HIPES, in coordination with the retarded oxidation process of CSO. The texture and stability of CSO-HIPESG were determined superior to commercially cream, especially for plasticity and water retention capacity. These findings further validated the potential of CR/SDG-encapsulated CSO as an exceptional interfacial stabilizer for HIPESG applications.

Ultrasonic combined pH shifting strategy for improving the stability of emulsion stabilized by yeast proteins: Focused on solubility, protein structure, interface properties

In this study, the improvement mechanism of yeast proteins (YPs) with the ultrasonic and pH shifting treatment on the emulsion stability was investigated through the solubility, protein structure and interface behavior of YPs. Compared with only pH shifting or ultrasound treatment, the solubility of YPs with the combined treatment of ultrasonic and pH shifting was increased significantly. The soluble protein content of pH-U400 reached 85.51 %. The results of YPs structure demonstrated that the β-sheet, α-helix and disulfide bonds contents of YPs with the combined treatment first declined and subsequently increased with increasing ultrasonic power, under alkaline conditions. The fluorescence intensity and surface hydrophobicity first increased and then declined. The more flexible protein structure endowed pH-U400 with lower interfacial tension, higher interfacial diffusion, penetration and reorganization rate, and interfacial protein concentration. The pH-U400 showed the best emulsifying properties (emulsifying activity index was 27.05 m2/g, emulsifying stability index was 31.27 min) and could prepare smaller and more uniform emulsion droplet. The results of multiple light scattering demonstrated that emulsion stabilized by pH-U400 showed the best stability. These results revealed the stability mechanism of emulsions stabilized by YPs and provided guidance for further development of practical YPs products in the food industry.

Role of ultrasound and pectin in regulating the foaming properties and baking applications of liquid egg white

The capacity of liquid egg white (LEW) to generate foam has become crucial in food processing. This study investigated the impact of ultrasound (US) and pectin in regulating the foaming properties and baking applications of LEW. Results showed that US treatment combined with pectin significantly (P < 0.05) improved foam ability (FA) from 142 ± 3.464 % to 236 ± 2.65 % and foam stability (FS) from 33.32 ± 2.63 % to 60.4 ± 1.82 %. The lowest surface tension achieved was 44.691 mN/m for EW600 + 1 % P. High-intensity US and pectin also enhanced the ξ-potential, solubility, and surface hydrophobicity. Dynamic rheological analysis indicated increased in apparent viscosity and viscoelasticity. Furthermore, increasing US power led to significant turbidity enhancements, rising from 41.22 ± 0.093 % to 96.30 ± 0.026 % (P < 0.05). Importantly, angel cakes made from US-treated LEW with pectin showed a higher specific volume, with EW600 + 1 % P reaching 3.2297 ± 0.017 mL/g compared to 2.9258 ± 0.022 mL/g for the control (P < 0.05). These findings suggest that US and pectin enhance foaming rates and baking performance, addressing reduced FS in egg whites (EW) and angel cakes when different US treatments were applied alone.

Interfacial Properties and Structure of Emulsions and Foams Co-Stabilized by Span Emulsifiers of Varying Carbon Chain Lengths and Egg Yolk Granules

Interfacial properties significantly influence emulsifying and foaming stability. We here explore the interfacial behavior of egg yolk granules (EYGs) combined with various Span emulsifiers (Span 20, 40, 60, 80) to assess their solution properties, interface dynamics, and effects on emulsifying and foaming stability. The results unveiled that as the Span concentration increased, particle size decreased from 7028 to 1200 nm, absolute zeta potential increased from 4.86 to 9.26 mv, and the structure became increasingly loosened. This loose structure of EYGs-Span complexes resulted in reduced interfacial tension (γ), higher adsorption rate (Kd), and improved interfacial composite modulus (E) compared with native EYGs. These effects were more pronounced with shorter hydrophobic chain Spans but diminished with longer chain lengths. Enhanced interfacial properties contributed to better emulsification and foaming stability, with EYGs-Span complexes displaying increased emulsifying ability and stability compared with natural EYGs. Emulsifying and foaming stability improved in the order of Span 20 > Span 40 > Span 60 > Span 80 as the Span concentration increased. The correlation analysis (p > 0.05) indicated that emulsifying stability was positively associated with interfacial composite modulus and negatively correlated with particle size. Consequently, EYGs-Span composites demonstrate considerable potential for use as effective emulsifiers in food industry applications.

Ovalbumin/sodium alginate Pickering emulsion: Structural characteristics and its contribution to enhancing the gel properties of Hairtail (Trichiurus haumela) surimi

In this study, ovalbumin (OV) and sodium alginate (SA), two macromolecular complexes, were coagulated into the emulsifier (OV/SA), which stabilized soybean oil by electrostatic interaction, hydrophobic interactions, and hydrogen bonding. The structure of OV/SA and properties of OV/SA Pickering emulsion were investigated. Additionally, the effect of emulsions on the gel and protein properties of hairtail surimi was studied. The results revealed that with the increasing concentration of OV/SA, the particle size and zeta potential value (negative value) of the emulsion initially decreased and then increased, while the rheological properties gradually improved. Compared with the surimi gel directly supplemented with soybean oil, the addition of emulsion enhanced gel strength, whiteness, water holding capacity, and hydrophobic interactions, resulting in a more stable gel network structure. In summary, incorporating emulsion into surimi at the same lipid content not only maintained its gel properties but also improved its color and compensated for lipid loss.

High internal phase Pickering emulsions stabilized by egg yolk-carboxymethyl cellulose as an age-friendly dysphagia food: Tracking the dynamic transition from co-solubility to coacervates

Although protein-polysaccharide complexes with different phase behaviors all show potential for stabilizing high internal phase Pickering emulsions (HIPPEs), it is not clarified which aggregation state is more stable and age-friendly. In this study, we investigated and compared the stability and age friendliness of HIPPEs stabilized with egg yolk and carboxymethyl cellulose (EYCMC) in different phase behaviors. The results revealed differences in particle size, aggregation state, charge potential, and stability of secondary and tertiary structures of EYCMC. The behavior of EYCMC at the oil-water interface was mainly divided into three phases: rapid diffusion, permeation, and reorganization. The electrostatic interaction, kinetic hindrance, and depletion attraction were the mechanisms primarily involved in stabilizing HIPPEs by EYCMC. Rheological analysis results indicated that HIPPEs had excellent viscoelasticity, structural recovery properties and yield stress. HIPPEs were used in 3D printing, electronic nose testing, IDDSI testing and in vitro digestive simulations for the elderly, demonstrating a fine appearance, safe consumption and bioaccessibility of β-carotene. Soluble complexes showed the best stability and age friendliness compared to other aggregated forms. This study serves as a foundational source of information for developing innovative foods utilizing HIPPEs.

Development and characterization of curcumin-loaded chitosan/egg yolk freshness-keeping edible films for chilled fresh pork packaging application

In this study, a novel fresh-keeping edible film was prepared using egg yolk (EY) and chitosan (CS) with varying concentrations of curcumin (Cur) for food packaging. The addition of Cur notably enhanced tensile strength, elongation at break, and water resistance from 15.70 MPa to 24.24 MPa, 43.79 % to 63.69 %, and 1.599 g·mm·(m2·h·kPa)-1 to 1.541 g·mm·(m2·h·kPa)-1, respectively. Cur also impacted moisture content, swelling degree, and film color. SEM revealed a uniform distribution of Cur, creating a smooth and dense film surface. FT-IR analysis suggested that hydrogen bonding facilitated Cur integration into the film network. The films demonstrated excellent UV-blocking and antioxidant properties attributed to Cur's chromogenic and phenolic hydroxyl groups. Consequently, they effectively inhibited lipid oxidation and weight loss in meat, thereby prolonging the shelf-life of chilled pork by at least 2 d. In conclusion, this study provided a simple and cost-effective idea to incorporate actives with EY as a natural emulsifier, presenting an effective solution for developing active packaging materials to enhance the safety and quality of meat products.

Emulsifying properties of egg proteins: Influencing factors, modification techniques, and applications

As an essential food ingredient with good nutritional and functional properties and health benefits, eggs are widely utilized in food formulations. In particular, egg proteins have good emulsification properties and can be commonly used in various food products, such as mayonnaise and baked goods. Egg protein particles can act as stabilizers for Pickering emulsions because they can effectively adsorb at the oil-water interface, reduce interfacial tension, and form a stable physical barrier. Due to their emulsifying properties, biocompatibility, controlled release capabilities, and ability to protect bioactive substances, egg proteins have become ideal carriers for encapsulating and delivering functional substances. The focus of this review is to summarize current advances in using egg proteins as emulsifiers. The effects of influencing factors (temperature, pH, and ionic strength) and various modification methods (physical, chemical, and biological modification) on the emulsifying properties of egg proteins are discussed. In addition, the application of egg proteins as emulsifiers in food products is presented. Through in-depth research on the emulsifying properties of egg proteins, the optimization of their applications in food, biomedical, and other fields can be achieved.

Protein aggregation caused by pasteurization processing affects the foam performance of liquid egg white

Pasteurization is necessary during the production of liquid egg whites (LEW), but the thermal effects in pasteurization could cause an unavoidable loss of foaming properties of LEW. This study intended to investigate the mechanism of pasteurization processing affects the foam performance of LEW. The foaming capacity (FC) of LEW deteriorated significantly (ΔFCmax = 72.33 %) and foaming stability (FS) increased slightly (ΔFSmax = 3.64 %) under different temperature-time combinations of pasteurization conditions (P < 0.05). The increased turbidity and the decreased solubility together with the decreased absolute value of Zeta potential indicated the generation of thermally induced aggregates and the instability of the protein particles, Rheological characterization demonstrated improved viscoelasticity in pasteurization liquid egg whites (PLEW), explaining enhanced FS. The study revealed that loss in foaming properties of PLEW resulted from thermal-induced protein structural changes and aggregation, particularly affecting FC. This provided a theoretical reference for the production and processing of LEW products.

Mechanism for improving the in vitro digestive properties of coconut milk by modifying the structure and properties of coconut proteins with monosodium glutamate

In this paper, the effect of monosodium glutamate (MSG) on coconut protein (CP) solubility, surface hydrophobicity, emulsification activity, ultraviolet spectroscopy and fluorescence spectroscopy was investigated. Meanwhile, the changes in the in vitro digestive properties of coconut milk were also further analyzed. MSG treatment altered the solubility and surface hydrophobicity of CP, thereby improving protein digestibility. Molecular docking showed that CP bound to pepsin and trypsin mainly through hydrogen bonds and salt bridges. And MSG increased the cleavable sites of pepsin and trypsin on CP, thus further improving the protein digestibility. In addition, MSG increased the Na+ concentration in coconut milk, promoted flocculation and aggregation between coconut milk droplets, which prevented the binding of lipase and oil droplets and inhibited lipid digestion. These findings may provide new ideas and insights to improve the digestive properties of plant-based milk.

Fat analogue emulsions stabilized by peanut protein microgel particles: microscale and nanoscale structure and stabilization process analysis

BACKGROUND

Biopolymer-based microgels are being regarded increasingly as promising building blocks in food applications. This study aimed to clarify the evolution process of the network for fat analogue emulsions stabilized by peanut protein isolate (PPI) microgel particles. It also investigated the interfacial structure and characteristics of emulsions (50% oil phase, w/w) stabilized by microgels under different pH conditions.

RESULTS

There was an increasing interfacial adsorption capacity for PPI microgels over time (from 85.26% to the maximum of 89.78% at 24 h of storage) due to the aggregation of microgels around droplets and the development of cross-linking microgel chains between adjacent interfaces. The increased β-sheet content (from 35.51% to 41.12%) of adsorbed microgels indicated unfolding and the enhanced aggregation of microgels, which led to stronger droplet interaction. The network evolution observed with different microscopes clarified the transition to a self-supporting emulsion. The uneven adsorption of large microgel aggregates at the oil-water interface promoted larger and deformed droplets, so more fat-like medium internal phase emulsion stabilized by PPI microgel could be obtained by adjusting the microgel pH to 4.5. The interfacial membranes observed by scanning electron microscopy were thicker and coarser at pH 3.0 and 4.5 than those at pH 7.0 and 9.0. The adsorption of PPI microgel aggregates enhanced the structural strength and improved emulsion stability.

CONCLUSION

This work could form a basis for further studies relating physical properties to the design of plant protein-based fat analogues. © 2024 Society of Chemical Industry.

Molecular Modeling of the Adsorption of an Egg Yolk Protein on a Water-Oil Interface

Egg yolk contains several molecular species with emulsifying properties, such as proteins and phospholipids. In particular, these molecules have both polar and nonpolar parts and thus can act as surfactants. One of the most surface-active proteins from egg yolk low-density lipoproteins is the so-called Apovitellenin-1. Experimental studies have been hindered by difficulties in isolating individual species from egg yolk lipoproteins. The purpose of this work was to assess the emulsifying properties of Apovitellenin-1 and any potential cooperative or competitive behavior in the presence of phospholipids. To do so, molecular simulations were carried out in a liquid-liquid interfacial system consisting of water and soybean oil, with varying concentrations of phospholipids and for different spatial configurations. To evaluate the conformational stability of the protein at the water-oil interface, the Gibbs free energy was computed from Metadynamics simulations as a function of the distance from the interface and of the radius of gyration. Moreover, a detailed analysis was also performed to determine which peptide residues were responsible for the protein adsorption at the oil-water interface as well as the lowering of the interfacial tension. Lastly, we combined the simulation results with a thermodynamic model to predict the interfacial tension behavior at increasing protein bulk concentration, which cannot be measured experimentally.