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The effects of three different enzyme treatments on the structure and volatile compounds of egg yolk protein were investigated. The secondary and tertiary structures, as well as volatiles, were characterized using ultraviolet spectroscopy (UV), fourier transform infrared (FTIR) spectroscopy, free sulfhydryl group analysis, and gas chromatography-mass spectrometry (GC-MS). FTIR analysis revealed a decrease in the contents of intermolecular, intramolecular, and intermolecular antiparallel β-sheets while an increase in random coils was observed. The contents of α-helices and β-turns did not show significant changes, indicating a reduction in protein compactness. Enzymatic treatment led to an increase in hydrophobic interaction, electrostatic interaction, and hydrogen bond formation within the egg yolk hot gel (EYG). Structural characterization demonstrated that EYG formed large uniform air chamber cavities after lipase hydrolysis (LEYG), while EYG hydrolyzed by papain (PEYG) and by flavor protease (FEYG) exhibited more compact structures. In addition, the binding of proteins to flavor substances inhibited the release of volatile flavor compounds. These findings provide insights into enhancing the flavor and texture of egg yolk by modulating its protein structure. [Display omitted] • The enzyme treatment induced a significant alteration in the secondary structure, resulting in increased flexibility. • The flavor components potentially formed hydrophobic interactions with egg yolk, thereby improving their flavor profile. • The alteration of free sulfhydryl group could potentially result in a reduction in gel strength. • The interrelation among protein structure, gel texture, and flavor was investigated through diverse analytical approaches. [ABSTRACT FROM AUTHOR]

This study investigated the effects of heat treatment (at 72, 76, 80, 84 °C for 2, 4, 6, 8, 10, 12 min) on the rheological, microstructural, protein structures and 3D printing characteristics of egg yolk. The results showed that the storage modulus (G′), loss modulus (G″) and viscosity exhibited an increasing trend with increasing heating time. Confocal laser scanning microscope (CLSM) showed that after heating for 8 min at 76 °C, 80 °C and 84 °C, lipids were released from viscous yolk paste, followed by second recombination and aggregation among yolk components. At these points above, the solid behaviors (G' ≥ G″) of egg yolks were observed, which caused a restraint of proton migration of water and lipid. Fourier transform infrared spectroscopy (FTIR) demonstrated that after heating at 72 °C for 8 min, 76 and 80 °C for 6 min and 84 °C for 4 min, a left shift began to appear in the heat-induced egg yolk paste at wavenumber 1631 cm−1, which were in accordance with a decrease in the shorter relaxation time (T 21) and fluorescence intensity and an increase in apparent viscosity of egg yolks. The results of printing performance showed that the viscous yolk pastes induced by heat treatment (at 76 °C for 8 and 10 min or 80 °C for 6 min) can be used for 3D printing. Image 1073 • Heat-induced egg yolk paste can be used for 3D printing without additives. • LF-NMR, FTIR was used to reveal protein, lipid and water mobility and hydrogen bond. • Best printing performance of yolk was obtained by heat treatment at 76 °C for 8 min. • HDL plays a particular role in the formation of high-viscous heat-induced egg yolk. • Relationship between rheology, protein structure and printing behavior was analyzed. [ABSTRACT FROM AUTHOR]

The physicochemical properties, rheology, texture, water state and microstructure of gels formed from different ratio of egg proteins and soybean protein isolate were investigated. Results showed that composite solution that contained 75% egg proteins had the highest protein surface hydrophobicity while the biggest solubility was found when the proportion of egg proteins was 25%. Solid content and total sulfhydryl groups content before centrifugation increased as the proportion of egg proteins raised while total sulfhydryl groups content after centrifugation had less fluctuations because of the changes of protein solubility. Egg proteins-soybean protein isolate composite solutions had various growth ratio of G' during different stages of solution-gel transition process, suggesting the composition of the solutions affected the molecular interactions and then changed the gelling properties. Besides, composite gels that contained the whole egg had higher hardness and lower springiness than those gels that contained egg yolk. The gel hardness after 50% addition of the whole egg and egg yolk was about 561% and 329% of the original gel strength while the gel springiness was 0.91 and 0.94, respectively. From results of microstructure, egg yolk-soybean protein isolate composite gels possessed denser gel network, which may be related with higher solid content of egg yolk. Conversely, the whole egg-soybean protein isolate composite gels showed rigid fiber network with holes, leading to better water mobility, higher hardness and lower springiness. Image 1 • Properties of gels made with egg proteins and soybean protein isolate were studied. • The interaction between proteins promoted the exposure of hydrophobic groups. • Adding egg proteins is a good way to increase gels' hardness and keep springiness. • Egg proteins, especially egg yolk, increased the water stability of composite gels. [ABSTRACT FROM AUTHOR]

Abstract The foaming characteristics (foam ability, foam stability and foam microstructure) of fresh foams based on egg white protein, and with the addition of different proportions of egg yolk and yolk fractions (plasma and granules) were analyzed in this research. The relationships between foaming properties and addition of yolk fractions were carried out via surface tension, surface hydrophobicity, apparent viscosity and zeta potential. The results showed that charge properties of yolk fraction dispersions were considered to have positive correlations with their foam stability to egg white. The foam abilities might possibly be determined by their particular structure and interactions with egg white protein. Besides, their interactions could also be represented by surface tension and surface hydrophobicity. Therefore, this study provides a new insight for determining the relationship between foaming properties of egg white contaminated by proportions of egg yolk fractions and the physicochemical properties of egg white/yolk or yolk fractions dispersions. Graphical abstract Image 1 Highlights • Foaming properties of egg white-yolk/fractions were studied. • Components and Structures in yolk/fractions influenced foaming characterization. • Surface indexes dominated foam properties of egg white-yolk/fractions dispersions. • Surface charge resulted in high foam stability of egg white/granules bubbles. [ABSTRACT FROM AUTHOR]

The effects of NaCl addition on the gelling and water holding properties of egg white/yolk gels were studied via solubility, surface hydrophobicity, reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier transform infrared spectra (FTIR), textural analysis, low-field nuclear magnetic resonance (LF-NMR) and centrifugation. Results showed that more solubility and surface hydrophobicity increase of egg yolk dispersions were observed than that of egg white dispersions. SDS-PAGE results indicated that the different change trend of surface hydrophobicity between two egg proteins was closely related with the dissociation of egg yolk granule proteins. NaCl-induced protein heat denaturation will result in the decrease of ordered secondary structure (α-helix and β-sheet) by breaking hydrogen bond for both egg protein gels. A rapid decrease ( p < 0.05) in fracture strength/strain of egg white gels was found as the NaCl increased, while the fracture strength/strain of egg yolk gels first rose and then descended, indicating that the significant increases of solubility and hydrophobicity of egg yolk dispersions at a certain NaCl concentration (≤1.8%) were benefit to the formation of strong molecule interaction among gel network. Results from LF-NMR and centrifugation water holding capacity (WHC) tests revealed that NaCl addition affected the WHC of egg white gels by increasing the mobility and distribution of free water, and had a complex influence on proton mobility and relaxation peak changeability of egg yolk gels due to the interaction among lipid, protein and water. [ABSTRACT FROM AUTHOR]

In this study, alginate/κ-carrageenan hydrogel beads were developed to encapsulate and release egg yolk immunoglobulin Y (IgY) under simulated gastrointestinal conditions. The effects of κ-carrageenan concentration on the encapsulation and loading efficiency of the hydrogel beads was assessed, as well as on their swelling and release behavior in a simulated human gut. An κ-carrageenan concentration of 0.30% gave the optimum encapsulation and loading efficiency. After incubation in simulated gastric fluids, there was no loss in IgY activity when it was encapsulated within alginate/carrageenan beads but around 35% loss when it was encapsulated in pure alginate beads. This effect was attributed to a stronger electrostatic attraction and a more closely packed biopolymer network formed within the composite beads, based on measurements of their electrical and microstructural properties. The composite beads were resistant to swelling in the stomach phase, but not in the intestine phase. The kinetics of swelling under simulated gastric conditions was found to follow Schott's second-order model. The gastrointestinal digestion of the IgY was slower in the composite beads than in the pure alginate beads. The release kinetics of IgY from the composite beads was fitted by an irregular release model. Our results suggest that alginate/κ-carrageenan composite beads are efficient carriers for the delivery systems of hydrophilic immunoglobins. Image 1 • A high encapsulation efficiency of IgY in alginate/carrageenan beads was achieved. • Alginate/carrageenan beads had a denser internal microstructure than alginate ones. • 0.3% carrageenan gave strong protection of IgY-loaded beads in gastric conditions. • Release kinetics of IgY from beads was fitted best by an irregular release model. [ABSTRACT FROM AUTHOR]

In this study, the interactions between egg yolk granule and soybean lecithin and their emulsion properties were investigated. For egg yolk granule, the increase of solubility and negative zeta-potential and decrease of hydrophobicity could be observed with the increase of lecithin concentrations, indicating the interactions between granule protein and lecithin. Results from the z-average particle size and the AFM image showed that the increase of solution pH and addition of lecithin could destroy the aggregated structure of the egg yolk granule. The disrupted granule exhibited better emulsion stability than that of native granule due to the higher surface charge and lower particle size. Notably, appropriate addition of lecithin (less than 0.25%) would be conducive to the formation of high stable emulsions by modestly reducing the contact angle, while extra lecithin (more than 0.50%) would induce excessive substitution of granule protein by competitive adsorption, leading to destabilization of the O/W emulsions via surfactant-induced depletion flocculation. Image 1 • The increase of solution pH and addition of lecithin could dissociate the egg yolk granule. • Dissociation of egg yolk granule was beneficial to emulsion stability. • Excessive displacement of interface granule proteins by lecithin resulted in stratification. [ABSTRACT FROM AUTHOR]

Egg yolk is an indispensable ingredient in the preparation of food emulsions due to its unique nutritional value and functional properties. However, egg yolk is sensitive to heat treatment and has poor emulsifying stability, which can be a limitation to the application of egg yolk in food industry. This study, the effect of neutral and alkaline protease (2,000U/g egg yolk protein) on thermal stability and emulsifying properties of egg yolk was investigated. Results showed that the hydrolysed egg yolk had higher thermal stability and emulsifying stability, especially for the samples hydrolysed by alkaline protease. The molecular weight of hydrolysed egg yolk protein was smaller than others as proved by electrophoresis and a considerable increase of protein solubility was observed. In addition, hydrolysis changed the degree of ionization of amino acids, increasing its static charge. The smaller molecular weight of the protein and the higher electrostatic charge delayed the gelation point, improving the thermal stability of the egg yolk. The emulsifying stability of hydrolysed egg yolk was improved, possibly resulting from the increase of soluble protein or polypeptide. Emulsions made with hydrolyzed egg yolk exhibited smaller particle sizes and higher surface charges, thus improving creaming stability of emulsions. Image 1 • Hydrolysis increased solubility by increasing net charge of egg yolk protein. • Hydrolysis improves heat resistance of egg yolk. • Hydrolysis increases creaming stability of egg yolk stabilized emulsions. • Alkaline protease has the best improvement effect on heat and emulsion stability. [ABSTRACT FROM AUTHOR]