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Background Hen egg yolk (EY) has a variety of techno-functionalities, including emulsifying, gelling, and film-forming properties. However, the application of native EY and its fractions is still limited due to the insufficient functionalities. Thus, various modification treatments have been used to improve the functionalities. In addition, there has been increasing research interest to explore the potential of modified EY and its fractions for applications in developing value-added food products. Scope and approach This review provides a brief introduction of EY structures, fractions, and components and focuses on discussing a wide range of existing modification methods and the mechanism of each method to change the structure and improve the desirable functionality of EY and its fractions. Three emerging applications of EY in food formulation industry, i.e. nutrient encapsulation and delivery system, unmodified EY substitutes, and edible films, are finally highlighted. Key findings and conclusion Recent studies have shown that pre-treatment of EY and its fractions are often needed using enzymatic hydrolysis, complexing with polysaccharides, or other chemical, physical, and fermentation methods. The purpose of the pre-treatment is to dissociate the aggregated EY protein state, modify solution characteristics (such as solubility, hydrophobicity, and surface charge), so that the functionality is greatly improved, leading to more stable emulsion systems or other novel EY-based food products. By reviewing the new modification technology and application trends of EY, this review provides expert opinions of future research directions for the development of value-added EY derived food products.

BACKGROUND: Liquid eggs have the advantages of high hygiene security, easy use, and convenient transportation, but their shelf life is only limited to 2~3 weeks. The microbial, physiochemical, and functional properties of pasteurized LWE were investigated in this study to evaluate the quality of pasteurized liquid whole egg (LWE) during refrigerated storage. RESULTS: The tested shelf life of the pasteurized LWE was 16 days when stored at 4 °C. During refrigerated storage, Pseudomonas gradually became the dominant bacterium in LWE following lactic acid bacteria, although the initial number of Pseudomonas after pasteurization was relatively limited (

This study investigated the encapsulation of curcumin into egg white protein (EWP) nanoparticles. Processing conditions used to formulate the nanoparticles, including pH and the addition of ethanol, were used to control the unfolding and aggregation behavior of EWP. The curcumin loading capacity of the EWP nanoparticles was found to be strongly linked to the structural transitions of the protein during heat denaturation, and the microscopic properties of the particles such as particle size and zeta-potential. Fibrous particles were formed at lower pH (3.0) and were associated with a higher curcumin loading than the granular particles formed at pH 3.8. Ethanol leads to an increase in β-sheet structure, and the formation of a coarser gel structure during heat denaturation, resulted in an increase in particle diameter. The highest curcumin loading capacities were 11.53 and 9.89 mg/g protein (with a final curcumin concentration of 312.5 μM and 268 μM respectively), at pH 3.0 and 3.8, respectively. Encapsulation in EWP nanoparticles was shown to both effectively slow the degradation ratio as well as protect the antioxidant activity of encapsulated curcumin.

Egg gel is the combined gelation of egg white (EW) and egg yolk (EY); its properties depend on the fixed ratio of EW and EY in shell egg. This study investigated the gelation properties of egg mixtures in artificial blends to explore innovative egg solutions catering to the market demands and provide guidance for the production of creative egg products. Results showed that solubility of samples decreased with the increase of EY proportion while solid content increased. More surface hydrophobicity and total SH group increases were observed with higher EY proportion. Rheological tests suggested that adding EY decreased samples' initial G' values. Egg gel containing 20% EY presented the largest hardness value, which seems to be related to the fine gel network microstructure. Besides, the springiness and water-holding capacity of gels gradually increased with EY addition, which may be the result of dense microstructure and high solid content of EY.

BACKGROUND: Egg proteins are effective emulsifiers and gelators in food systems. However, the physicochemical stability and control release properties of egg-protein stabilized emulsions and gels need to be further improved. The potential of sodium tripolyphosphate (St) to improve the functionality of egg proteins was evaluated. RESULTS: The emulsions with St had smaller particle sizes and higher zeta potential, leading to better physical stability. Furthermore, the oxidation stability increased with increasing St contents, possibly due to its metal chelating capacity and the improved emulsifying activity of whole-egg dispersions. Phosphate had a positive impact on the chemical stability of β-carotene in whole-egg liquids and gels, decreasing the degradation during thermal treatment. The gel made with St was firm and broke down slowly, leading to a low rate of digestion and β-carotene release in simulated gastric fluid. CONCLUSION: This study shows that St is useful to improve the egg proteins stabilized emulsions and gels, which is applicable in the development of emulsion-based food grade gel products. © 2021 Society of Chemical Industry.

In this study, the stability of 5-methyltetrahydrofolate (5-MTHF) in the model system and folate-enriched egg yolk and strategies for 5-MTHF stabilization were investigated. The oxygen, temperature and light affect the stability of 5-MTHF in the model system, among which oxygen is the main factor. In thermal pasteurization and spray-drying with normal air media, 5-MTHF is sensitive to oxidation, with the retention rate of blank group only reaching 74.96% ± 1.28%. The addition of vitamin C or vitamin E can protect 5-MTHF in egg yolk from degradation and the latter has a better protective effect. By adding 0.2% (w/v) vitamin E to egg yolk liquid, the retention rate of 5-MTHF during thermal pasteurization and spray-drying with normal air media were 94.16% ± 0.48% and 84.80% ± 0.82% respectively. Additionally, the spray-drying technique with inert gas media (N(2)) was also an effective method to improve the stability of the 5-MTHF in egg yolk. Our study explored the factors affecting the stability of 5-MTHF in both model systems and egg yolk liquid and provided effective strategies for the protection of 5-MTHF during the processing of egg. [Image: see text]

BACKGROUND Egg yolk, as a natural emulsifier, is widely used in high-oil-phase food systems, such as mayonnaise and salad. However, the application of egg yolk in an oil-in-water system is still limited due to poor emulsifying stability. To improve the emulsifying capacity of egg yolk, the effect of chitosan addition sequence and concentration on emulsifying properties (creaming stability, thermal tolerance and oxidation resistance) of egg yolk hydrolysates were investigated. RESULTS Stacking sequence of multilayer materials has an influence on properties of composite emulsions. The composite emulsions with egg yolk hydrolysis dominate at the interface (functioning on reducing interfacial tension), and chitosan layered on the surface (providing steric hindrance) displayed better stability. Little chitosan addition (0.5 g × kg-1 , w/w) was unhelpful for the dispersion of emulsion droplets as a result of bridging flocculation. At a chitosan concentration of 2 g kg-1 (w/w), the composite emulsion possesses the best stability. When chitosan concentration was higher than 2 g kg-1 (w/w), depletion flocculation would occur. Hydrolyzed egg yolk prepared composite emulsions possessed better thermal resistance, but with poorer oxidative stability as compared to natural egg yolk. In combination with chitosan it also displayed a negative effect on the oxidative stability of the emulsion system. CONCLUSION The research revealed the effect of chitosan addition on the physical and chemical stability of emulsions prepared with egg yolk hydrolysates. The results could provide guidance on expanding the application of egg yolk as an emulsifier in water-abundant food systems such as beverages. © 2021 Society of Chemical Industry.

Individual and synergistic effects of sodium chloride (NaCl) and sodium tripolyphosphate (STPP) on the physicochemical and gelling properties of highly diluted liquid whole eggs were studied. Results showed that NaCl and STPP acted differently whereby NaCl addition increased the surface hydrophobicity of the egg proteins and STPP addition increased the protein solubility and the negative surface charge. When combined together, these changes led to a significant increase in a number of intermolecular forces after heat treatment, including hydrophobic interactions, disulfide bonds, and hydrogen bonds, contributing to the best structure and texture of the whole egg gels enriched with binary salts. The amount of the free water in the heat-induced gel products with the addition of both NaCl and STPP were the least as compared to systems with single salt addition, which was related to the coarse and dense network microstructure.

This study, three different procedures were used for preparation of egg white protein (E) and egg white protein fibrous microparticle (EM) complex emulsions, to modify the interfacial and aqueous composition. According to the adding order of EM and E during emulsification, the emulsions were named as type I (EM and E mixed firstly, followed by emulsification), type II (emulsified with EM firstly, followed by the addition of E) and type III (emulsified with EM firstly, followed by the addition of E). The particle size, creaming stability at various salt concentration, elastic module (G’), and lipid oxidation degree were investigated. The results showed that, EM at interface is beneficial for improving salt resistance of the complex emulsions, while E was more effective in terms of preventing oxidation of oil, attributed to the possibility to form continuous elastic interface film. The type III complex emulsion at EM:E ratio of 2:1 showed both improved creaming and oxidation stability, behaving the potential to be used as carrier of lipo-nutrients.

The salted egg yolk (SEY) is very popular in China for its pleasant flavor and texture. However, the long production cycle of traditional pickling and the waste of salted egg white had limited its industrialization. To solve these problems, a salted egg yolk flavoring was generated through enzymatic hydrolysis and microwave irradiation from fresh egg yolk in this study. The combination of enzymatic hydrolysis and microwave irradiation could force water and lipids in egg yolk to migrate out, and lead to lipid oxidation in high temperature. Lipid oxidation and Strecker degradation were defined as the major pathways of flavor generation. Among the generated volatile compounds, Hexanal, Heptanal, Benzaldehyde and 2-Pentyl-furan were supposed closely related to SEY flavor. This method could be used as an alternative method for the production of salted egg yolk. Furthermore, it could provide a foundation for further investigation of egg yolk containing flavor system.

This study investigated the interaction between egg white protein particles (EWPP) and rhamnolipid (Rha) as co-emulsifiers in high internal phase emulsions (HIPEs). To reveal the effect between EWPP and Rha on the properties of HIPEs, the physicochemical properties (particle size, zeta-potential and microstructure) and emulsifying capacity were investigated. The results showed that, with the increase in Rha content, the EWPP-Rha complex could be divided into three regions according to the emulsifying capacity. The emulsion properties at different regions were analyzed by microstructure, rheology and nuclear magnetic resonance etc. The addition of Rha may compete interface with EWPP, adjusting the properties of constructed HIPEs. Generally, the replacement of EWPP by Rha from interface decreased emulsion droplets and disrupted the inter-droplet network, resulting to the formation of soft and flexible emulsions. The incorporation with Rha was beneficial for improving the emulsifying capacity of EWPP. In Rha sufficient system, more EWPP distributed in the aqueous phase of constructed HIPEs and functioned as a stabilizer to increase coalescence stability. The study was meaningful for revealing the complicated relation between protein particle and surfactant, and improving properties of high internal phase emulsions combining the advantages of each emulsifier.

The development of nutrient and bioactive delivery vehicles has become a burgeoning field with the worldwide growing demand for healthy foods and supplements. Food-grade protein particles have attracted significant attention for their great potentials in fabricating nutrient delivery vehicles. This review aims to summarize a wide range of food-grade protein particles used for the fabrication of nutrient delivery systems, with a particular focus on analyzing the digestion behaviors and nutrient release mechanisms using digestion models. The review of the current literature reveals that a variety of modification techniques exist to promote the formation of protein particles with desirable structures and physicochemical properties (particle size, surface charge, hydrophobicity, and interfacial wettability). Furthermore, nano/microparticles, hydrogels and Pickering emulsions have emerged as three main delivery vehicles based on food protein particles, and many studies have demonstrated their excellent ability to encapsulate and protect nutrients from degradation during storage and/or under exposure to light and heat. The digestion profile of these delivery systems and the release properties of nutrients are related to the composition, interfacial structure, and enzymatic responsiveness of the delivery system as well as the bulk environment. However, significant gap of knowledge still exists in the current understanding of these delivery systems at the biological interface. Future studies should focus on elucidating the digestion, the release of the encapsulated nutrients, and the intestinal absorption/transport using advanced simulated conditions and in in vivo models.

The effects of pH and NaCl on the physicochemical (zeta potential, particle size and surface tension) and interfacial properties (foaming and emulsifying properties) of egg white and yolk were investigated in order to protmote its applications in food industries. Results showed that the increase of foam expansion power/emulsifying activity index of egg white exhibited a good correlation with the decrease of particle size and increase of surface tension. However, the extra charge and decreasing surface tension of egg white/yolk dispersions at pH > 7.0/NaCl ≥ 0.6% resulted in the destabilization of foams. The emulsifying stability of egg yolk dispersions continued climbing to pH 10.0 due to the continuous reduction of particle size and started declining with the slow decrease amplitude of particle size at NaCl > 1.8%, thus z-average particle size is the main factor that dominates the emulsifying stability index of egg yolk dispersions. These results indicated that the foaming/emulsifying properties of egg white/yolk proteins can be manipulated by altering the physicochemical characteristics such as charge, surface tension and particle size in order to achieve optimal functional properties for food industrial applications.

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

The aim of this study was to verify the influence of selected phosphate salts (sodium diphosphate and trisodium phosphate) on the gelling properties and water state of whole egg gel. As shown by the results, the gel and water holding properties of whole egg was effectively improved after the addition of sodium diphosphate and trisodium phosphate, possibly through affecting the solubility, surface hydrophobicity, z-average particle size and pH of liquid egg dispersions. The difference in the viscoelastic properties of whole egg gels brought by two phosphate salts was related to their obvious difference in calculated ionic strength and pH. As the addition level of phosphate salts increased, the protein secondary structure after gelation was changed remarkably, characterized by the decrease of α-helix content and the increase of β-sheet content. The gel β-sheet content was positively correlated with fracture strain and percentage of bound water and immobilized water, while the α-helix content was negatively correlated with fracture strength. The scanning electron microscope (SEM) results showed that the addition of phosphate salts would facilitate the formation of a fine high strength stranded structure. Moreover, the color characteristics of whole egg gels can be more effectively improved by sodium diphosphate in comparison with trisodium phosphate.

Previously, it was shown that catechin-egg white protein (CT-EWP) conjugates were effective antioxidant emulsifiers that could form and stabilize emulsions, and also inhibit the degradation of encapsulated carotenoids. The objective of the current study was to evaluate the impact of conjugation on the in vitro bioavailability, cellular antioxidant activity, and cytotoxicity of β-carotene-loaded emulsions. Lipid droplets coated with EWP or with CT-EWP conjugates exhibited quite similar behavior when they were passed through a simulated gastrointestinal tract. The β-carotene encapsulated in emulsions stabilized by CT-EWP conjugates exhibited a higher overall in vitro bioavailability, which was attributed to a greater stability of the carotenoids to chemical transformation. The emulsions stabilized by CT-EWP conjugates also exhibited greater ability in inhibiting oxidation in a cell-based assay (dichlorofluorescein diacetate). Cytotoxicity analysis suggested that β-carotene emulsions stabilized by CT-EWP conjugates only exhibited a slight cytotoxicity when used at high concentrations. These results suggest that CT-EWP conjugates can be used to formulate emulsion-based delivery systems for chemically labile hydrophobic bioactives with enhanced antioxidant activity and bioavailability.

In this study, the effect of freeze–thaw treatment on isolation of IgY was investigated, with macrograph, protein concentration, solid content, and transmittance evaluated. The results showed that higher refrigeration power (at −18 °C for more than 4 h and −40 °C for more than 2 h) caused yolk gelation and was helpful for removing heteroproteins. To reveal the mechanism of freeze-induced gelation assisting isolation of IgY, the properties of yolk frozen at −5°C, −18 °C and −40 °C for 8 h were determined, with SDS-PAGE, rheology property, low field NMR and interactions between proteins evaluated. As the results showed, the purity of separated IgY increased obviously (frozen at −18 °C and −40 °C), corresponding to the removal of LDL which aggregated during freezing. LDL aggregation may be triggered by hydrophobic interaction during boundary water crystallization. Therefore, freeze-induced yolk gelation is beneficial for IgY isolation by keeping LDL in dense gel structure while releasing IgY to the supernatant.

Non-meat proteins are widely used in the meat processing, and the final product is greatly affected by salt. This study presented the combined use of soybean protein isolate (SPI) and egg white (EW) on the gelation of chicken myofibrillar protein (MP) with or with NaCl. Gel properties were determined with the use of texture profile analysis, cooking loss, intermolecular forces, rheological properties, scanning electron microscopy and low field nuclear magnetic resonance (LF-NMR) measurements. Non-meat proteins improved the MP gel quality when it was without NaCl, except for the increased cooking loss caused by 1.2% SPI. The effect of non-meat proteins on MP gel quality was more obvious at 0.3 mol/L NaCl, including the improvement of gel hardness by SPI and the reduction of cooking loss by EW. When the added non-meat proteins changed from 1.2% SPI to 0.3% EW-0.9% SPI, the gel hardness significantly decreased (P

The application of industrial egg white powder (EWP) was limited by the relatively poor foaming properties. Microwave treatment was proposed to be a creative and efficient technology to improve the functionality of EWP. This study focused on the physicochemical properties and baking performance of EWP undergoing microwave treatment at the presence of maltodextrin (MD). The solubility, fluorescent properties, molecular weight and secondary structure of protein were investigated to verify the glycation and structure transformation. The baking performance of the modified EWP was thoroughly investigated by foaming properties, specific volume, water content, microstructure, and sensory analysis. The microwave treated EWP at presence of MD showed smaller particle size and higher surface hydrophobicity than untreated EWP. The result of molecular weight distribution and FTIR spectrum verified the covalent binding of –OH abundant MD on the EWP molecule. The foaming ability of EWP after microwave treatment was increased from 4.84 mL/g to 6.18 mL/g at the presence of MD. The enhanced hydrophobic interaction and hydrogen bonding between protein molecules were the main beneficial factors affecting foaming properties and baking performance of EWP. This study was meaningful for promoting the application of microwave-assisted glycosylation reaction in the functional modification of proteins.

The efficiency of egg white protein microparticle (EWPM) and pectin sol (PS) addition in blocking flow behavior of light mayonnaise was investigated in this study. The texture properties, color, microstructure and thermal resistance were also measured for better understanding of synergistic effect of EWPM and PS on characteristics of light mayonnaise. At ratio of 2:4 (in weight ratio of PS and EWPM), the sample showed higher viscosity and hardness, attributed to the formation of larger protein aggregates induced by repulsion between protein and pectin molecule. The speculation was verified through the microstructure of mayonnaise samples observed by laser light confocal microscope. With the amount of EWPM increased, the yellow value of light mayonnaise increased, but thermal resistance decreased. For EWPM-rich samples, moderate heat treatment can strengthen the interaction between particles, inducing the increase of viscosity.

Colloidal delivery systems are required to encapsulate, protect, and release active food ingredients, such as vitamins, nutraceuticals, and minerals. In this study, lipid droplets were encapsulated within biopolymer microgels fabricated from egg white proteins using an injection-gelation process. Confocal fluorescence microscopy indicated that lipid droplets were dispersed within a network of cross-linked proteins within the microgels. The properties of the lipid-loaded microgels were compared to those of simple oil-in-water emulsions stabilized by egg white proteins. Light scattering and microscopy measurements indicated that both delivery systems exhibited good stability under acid conditions (pH 3-5) but aggregated at higher pH values as a result of a reduction in electrostatic repulsion. Simulated gastrointestinal tract studies indicated that lipid droplets encapsulated within protein microgels were digested more slowly than free lipid droplets. Our results therefore suggest that egg white protein microgels may be useful for encapsulation and controlled release of hydrophobic bioactive agents.

Transglutaminase (TGase) and succinylation could modify the physicochemical characteristics and the functional properties of proteins. The aim of this work was to cross-link egg white protein (EWP) and succinylated casein with TGase and to assess the feasibility of making a novel composite protein film. The effects of succinylated casein content, reaction time, and TGase concentration on the mechanical properties, physical characteristics (thermal property and degree of crystallinity), and structure properties (secondary structure and surface micrograph structure) of the film were investigated in this study. The results revealed that the susceptibility of EWP to TGase-mediated cross-linking modification was enhanced by succinylated casein. Meanwhile, the films with TGase were more homogeneous and smoother and possessed better water resistance and thermal stability. The content of α-helix, β-turn structures were increased whereas β-sheet structure was decreased. The spatial conformation and degree of crystallinity of composite protein film were also affected by TGase. The increase of the degree of crystallinity of the composite film further proved the improvement of film mechanical properties induced by TGase and succinylated casein. Based on the above results, this study provides relevant data and insights for the TGase/chemical modification of protein-based edible films.

The oxidation of unsaturated lipids commonly occurs at oil-water interfaces in heterogeneous foods (such as emulsions), and so there is a need for surface-active antioxidants to inhibit lipid oxidation. In this study, catechin was oxidatively polymerized by horseradish peroxidase to obtain catechin polymers (CTP). An amphiphilic antioxidant was then produced by conjugating CTP with egg white proteins (EWP) using a hydrogen peroxide-ascorbic acid pair as a radical initiator system. The covalent attachment of CTP to EWP was confirmed by electrophoresis, liquid chromatography-mass spectrometry, and fluorescence analyses. The antioxidant capacity of CTP-EWP conjugates was evaluated using several in vitro models. The conjugates exhibited strong scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (79% at 1 mg/mL), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (97% at 0.5 mg/mL), and had a high ferric reducing power. Furthermore, CTP-EWP conjugates exhibited an inhibitive effect on lipid peroxidation in linoleic acid oil-in-water emulsions, indicating that the conjugates may have potential applications in food, pharmaceutical and cosmetic industries.

Egg white protein is a kind of protein resource with distinctive nutritional value and functional properties, while performing weak emulsifying stability under neutral and alkaline conditions, limiting application in food industry. This study, we investigated the effect of enzyme on characteristics of egg white protein (EWP) and synergistic efficiency of pectin addition on properties (thermal stability, salt resistance and antioxidant activity) of emulsions stabilized by original or hydrolyzed EWP. The EWP solutions were incubated at pH 7.0, under 50 °C for 2 h, with various amount of enzyme (0%, 0.5%, 1%, 2%, and 4%) added in. With enzyme concentration increased, more ovotransferrin and ovalbumin were hydrolyzed, and more hydrophobic amino acids exposed to polar environment, especially tyrosine. In addition, the DPPH and ABTS radical scavenging activity of EWP increased with enzyme concentration increased. Pectin addition can effectively improve the stabilization of the emulsion droplets, inducing smaller effective diameter and polydispersity index. In comparison, the emulsions stabilized by hydrolyzed EWP with 0.3% pectin behaved better thermal and salty stability, while with poorer antioxidant capacity attributed to weaker intermolecular interactions. The rheological measurement showed that the viscosity of hydrolyzed EWP stabilized emulsion was relatively lower and G′ was more dependent on frequency, indicating weaker cross-links among droplets. The results may provide theoretical guidance for application of enzymatic and polysaccharide blends in improving protein functionality.

In this work, three methods were used for preparation of the emulsion. The mean particle diameter, ζ-potential, microstructure and stability of the emulsions coated by ovalbumin (OVA) and gum arabic (GA) were evaluated. The complexes (OVA/GA) and multilayer (OVA-GA) emulsions showed smaller droplet diameter (about 330 nm) above pH 3.3 and had a relatively good storage stability compared to the multilayer (GA-OVA) emulsion. Meanwhile, different stabilization mechanisms were identified. In the complexes (OVA/GA) emulsions, the OVA and GA formed complexes firstly that created an interface layer on the surface of the droplets. For the multilayer (OVA-GA) emulsion, the OVA adsorbed on the surface of the droplets, and then GA formed a double-layer structure by electrostatic interaction between the GA and the OVA. The multilayer (GA-OVA) emulsions showed a larger mean particle diameter due to the poor adsorption capacity of the GA compared with OVA. All emulsions revealed good thermal stability and no obvious change was observed. The experimental results demonstrated that the OVA/GA complexes could be used to prepare stable emulsion structures, which may be useful in the beverage industry.

This study investigated the potential of egg white protein (EWP) to be developed into a kind of Pickering stabilizer for oil-in-water emulsions. The EWP microparticles were formed by heating at 90 °C for 45 min, followed by homogenization under low pressure. The characteristics and microstructure of microparticles prepared under various pH (3.0, 3.8) and protein concentration (2–10%) were tested. Simultaneously, the properties of Pickering emulsions integrated by EWP microparticles, with fibrous or granular morphology, were investigated. At pH 3.0, the particles may transfer from fibrous structure to granular structure with protein concentration increased or salt addition. At pH 3.8, granular microparticles were formed under various protein concentration. The structure of EWP microparticles were mainly maintained by hydrophobic interactions and hydrogen bondings. The granular particles showed higher surface loading of protein and viscoelastic moduli in the integrated Pickering emulsions. These results have important implications for the formulation and production of emulsion based semi-solid products, using egg white protein as emulsifier and fat substitute.

Heat treatment is an indispensable processing step of seasoned liquid egg. The effects of preheat treatment (60–75 °C) on gel properties of liquid whole egg (LWE) at different NaCl concentrations (0–3%, w/w) were investigated to provide guidance for the production of salty LWE. Results showed that LWE exhibited higher particle size after heating, with coincidental increases in surface hydrophobicity and decreases in protein solubility. While LWE with NaCl added exhibited increase in protein solubility and decrease in particle size of aggregates. Electrophoresis and optical microscopy showed that NaCl would induce the transformation of egg granules from insoluble form to soluble form, inhibiting the aggregation of LWE proteins during preheat treatment, reflected by the reduced particle size. The analysis of gel aggregated force and texture indicated that NaCl addition and preheat treatment can improve gelling properties of LWE synergistically by strengthening the hydrophobic interaction and hydrogen bonds.

The purpose of this study was to evaluate the physicochemical stability and potential gastrointestinal fate of the lutein-enriched high internal phase emulsions (LE-HIPE) stabilized by egg yolk-modified starch complex. Results showed that the physical stability and lutein retention of the LF-HIPE stabilized by egg yolk-hydroxypropyl distarch phosphate (EY-HPDSP) or egg yolk-octenyl succinic anhydride starch (EY-OSA) complex were both significantly improved at 4 °C. However, the LE-HIPE stabilized by EY-HPDSP complex showed better physical stability, lower lipid oxidation and higher lutein retention during storage at 37 °C than that stabilized by EY-OSA complex, which was related with the results of smaller droplets, more restricted water and oil protons for the former. In vitro digestion results showed that high level of HPDSP in LE-HIPE was beneficial to the improvement of the bioaccessibility of lutein. These results could be useful in the development of nutrient delivery system based on egg yolk-modified starch complex stabilized HIPE.

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.

Thirteen samples representing five species were collected from different provinces of Southwest China, and their chemical composition, antihyperglycemic activity, and antioxidant activity were evaluated. These mushrooms had high crude protein (21.72–30.59 g/100 g dw) and total carbohydrate (49.18–62.58 g/100 g dw) contents, but low crude fat contents (1.96–7.87 g/100 g dw). They also accumulated notable quantities of potassium, zinc, sodium, magnesium and copper from the soil. The potassium content, in particular, was 18.75–39.21 times that found in the soil at the collection site. The natural habitat of these mushrooms, especially the mineral content of the soil, seems to have more influence on the mineral content of these mushrooms than their species. Most of the samples possessed antihyperglycemic and antioxidant activities. Suillellus luridus showed the highest antioxidant activity and antihyperglycemic activities, suggesting that S. luridus shows potential for development as a dietary nutritional supplement.

This study investigated the influence of acid (pH 3.0) or moderate heat (60 °C, 15 min, pH 3.0) treatments on physicochemical characteristics (ζ-potential and hydrophobicity), structure (Raman spectra) and emulsifying capacity of EWP after re-adjusted to various pH. Simultaneously, the stability of the emulsions prepared with acid and acid-heat induced EWP (AEP and AHEP) was tested by measuring particle diameter and microstructure of the droplets after salt (0–200 mM NaCl) and heat (90 °C, 30 min) treatments at pH 3.0–4.2. The results revealed that the emulsifying capacity of EWP was enhanced after acid or acid-heat treatment with more hydrophobic amino acids and charged groups exposed on the surface, but little changes in secondary structure. Proteins adsorbed at the oil-water interface were mainly ovotransferrin and ovalbumin. The emulsions made with AEP and AHEP were stable to droplet aggregation with no phase separation during storage for 3 weeks at pH below isoelectric point (pI ≈ 5.0), but exhibited some aggregation at pH near or above pI. The heat stability of emulsions depended on pH and thermal history. The emulsions made with AHEP performed better heat stability than AEP-stabilized emulsions. The salt stability of emulsions depended on the net charge. At pH 3.0, the emulsions were stable in the presence of ≤100 mM NaCl. At other pH, the emulsions showed good tolerance to 50 mM NaCl. These results have important implications for the formulation and production of emulsion based acid products, using egg white protein as emulsifier.

The stability, rheological and morphology properties of oil-in-water emulsions coated by ovalbumin (OVA)/gum arabic (GA) complexes were evaluated. At a ratio of 1:2, the emulsions showed better creaming and oxidative stability. Above or below 1:2, the emulsions were unstable due to depletion or bridging flocculation and the rates of lipid oxidation for 30-day storage were significantly higher. All emulsions exhibited elastic gel-like rheological properties. But the apparent viscosity (η) and storage modulus (G′) of emulsions at a ratio of 1:2 were higher than that of 1:1 and 1:3, which attributed to the electrostatic repulsion and ordered spatial structure of emulsions. Meanwhile, the Raman spectral results showed the OVA/GA complexes stabilizing system induced lipid chain disorder or lipid–protein interactions modifications, which may reflect the formation of a gel-like structure in the emulsion.

In this study, the influence of NaCl on the flocculation behavior and gel properties of egg yolk/κ-carrageenan mixed dispersions or emulsions were studied. As a result of NaCl incorporation, there was a decrease in the mean droplet size, zeta potential, degree of flocculation and viscosity of the mixed dispersions/emulsions, and the onset point of gelation was also brought forward. Increasing the concentration of NaCl led to a significant increase in gel strength and decrease in gel cohesiveness. Results from low field nuclear magnetic resonance (LF-NMR) confirmed that the addition of NaCl could significantly reduce the hydration ability of gel molecules and increase the content of immobilized water of hydrogels as the gel strength increased, while the water holding capacity of emulsion gels was depressed with the incorporation of oil. These findings suggested the flocculation state and gel properties of egg yolk/κ-carrageenan mixed dispersions/emulsions can be tailored by adjusting NaCl for food formulations.

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.

Dry heat treatment is normally used to improve foaming properties of egg white powder (EWP), which actually needs long production cycle with low efficiency. In this study, microwave technology was adopted to improve the foaming properties of EWP and the relationship between structure and foaming properties of EWP was investigated. The results showed that appropriate intensity of microwave treatment could induce the transition from β-sheet structures to α-helix and random coil structures. And the secondary structure of EWP after microwave treatment at 440 W for 6 min was 32.6% α-helix, 14.1% β-sheet, 17.5% β-turn and 35.8% random coil, which was similar to the structure of natural protein in egg liquid (unspray-dried). Meanwhile, the viscosity and flexibility of egg white protein were improved, which were beneficial to the protein adsorption at interface and enhancement of foam ability. Furthermore, the higher solubility and lower surface tension could be related to the fragmentation of microwave-treated egg white powder, which were helpful to the quick diffusion and adsorbance of egg white protein at interface. Therefore, the foam ability of EWP was raised to 4.84 mL/g after microwave treatment at 440 W for 6 min, having 15.3% higher than conventional dry-heat treated EWP.

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 (T21) 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.

Glycation with fructo-oligosaccharide (FO) and isomalto-oligosaccharide (IMO) was employed to improve the heat-induced egg white protein (EWP) gels. Results showed that EWP glycated with IMO exhibited a greater degree of glycation (DG) and better gelling properties than those of FO-EWP conjugates. The electrophoresis and liquid chromatography mass spectrometry (LC-MS) indicated that IMO was successfully covalently cross-linked with EWP. Fourier transform infrared spectroscopy (FTIR) showed that the glycation increased the percentages of intramolecular and intermolecular β-sheets of EWP and lowered the contents of 310-helical structure. The rheological test indicated that the gel-forming temperature of EWP was brought forward with the increase of glycation time. Furthermore, the glycation could induce the formation of EWP gel characterized by the higher strength of hydrogen bonds and hydrophobic interactions and lower strength of disulfide bonds. The changes of intermolecular forces resulted in a fine network structure of EWP gel, which significantly enhanced the fracture strength, bound water relaxation proportion and water-holding capacity (WHC) of the gel. A positive correlation existed in the WHC and gel fracture strength. This study proved that glycation with IMO efficiently improved the gelling properties of EWP.

The effects of dry-heat treatment (75 °C, 0–20 d) and guar gum (GG) composition on foaming properties and baking performance of egg white powder (EWP) were investigated. Rheological measurement showed that both dry-heat treatment and GG addition can improve the viscosity of EWP dispersion. The particle diameter of EWP dispersion decreased after dry-heat treatment, while hydrophobicity increased, indicating that the increased viscosity was caused by the enhanced hydrophobic interaction rather than particle induced steric hindrance. The sample undergoing 10 days of dry heating with GG addition performed the best foaming properties (foaming capacity 9.37 ± 0.26 mL/g and foaming stability 96 ± 1.56%). However, without GG addition, 10 days of dry heating just induced the foaming capacity and stability increasing from 5.17 ± 0.65 mL/g and 42.85 ± 2.90% to 6.96 ± 0.09 mL/g and 64.95 ± 3.04%, respectively. The sample EWP 10 + GG also exhibited the largest cake specific volume and uniform distribution of foams in cross section, which was observed in all three baking systems (low, middle and high sugar). In low sugar system, GG addition induced an increase in cake specific volume from 3.72 ± 0.02 mL/g to 4.55 ± 0.16 mL/g. The results revealed that combining dry-heat and GG addition can more effectively enhance foaming capacity and baking performance of EWP powder, providing guidance for its efficient application in baking industry.

Due to the poor thermal stability of egg white protein (EWP), important challenges remain regarding preparation of nanoparticles for EWP above the denaturation temperature at neutral conditions. In this study, nanoparticles were fabricated from conjugates of EWP and isomalto-oligosaccharide (IMO) after heating at 90 &deg, C for 30 min. Meanwhile, the effects of protein concentration, temperature, pH, ionic strength and degree of glycation (DG) on the formation of nanoparticles from IMO-EWP were investigated. To further reveal the formation mechanism of the nanoparticles, structures, thermal denaturation properties and surface properties were compared between EWP and IMO-EWP conjugates. Furthermore, the emulsifying activity index (EAI) and the emulsifying stability index (ESI) of nanoparticles were determined. The results indicated that glycation enhanced thermal stability and net surface charge of EWP due to changes in the EWP structure. The thermal aggregation of EWP was inhibited significantly by glycation, and enhanced with a higher degree of glycation. Meanwhile, the nanoparticles (&lt, 200 nm in size) were obtained at pH 3.0, 7.0 and 9.0 in the presence of NaCl. The increased thermal stability and surface net negative charge after glycation contributed to the inhibition. The EAI and ESI of nanoparticles were increased nearly 3-fold and 2-fold respectively, as compared to unheated EWP.

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.

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.

The effects of sodium tripolyphosphate and sugar on cold-set gel properties of egg yolk/κ-carrageenan/xanthan gum mixed dispersions were investigated by zeta potential, rheological measurements, gel textural analysis and low-field nuclear magnetic resonance (LF-NMR). As the yolk content increased to the 5 g/100 mL in aqueous systems, phase separation of mixed gel could be observed, due to the relatively rough gel appearance. Furthermore, the addition of phosphate could significantly improve the phase separation of mixed gels by elevating the pH and reducing zeta potential. The increase in the content of yolk and sugar brought an enhancement in gel storage modulus, while the addition of phosphate induced a dramatic decrease in the gelation rate of mixed gels. Textural analysis confirmed that hydrogen bonding interaction was the important force, which determined gel strength of the ternary composite cold-set gelation system. The result of LF-NMR revealed that there was a negative correlation between the decrease of proton mobility of immobilization water and the increase of gel strength in different sample series.

BACKGROUND The aim of this work was to evaluate the effects of egg freshness on baking properties and final qualities in batter systems. Batters were made with eggs of different freshness, and the properties of batter systems were studied through rheological analysis, rapid viscosity analysis (RVA), differential scanning calorimetry (DSC), batter density and expansion rate during the baking and cooling processes. Moreover, the qualities of final baked systems were investigated, including specific volume and texture profile analysis (TPA). RESULTS The flow behavior of batters showed that the consistency index (K) decreased as the Haugh unit (HU) value decreased, while the flow behavior index (n) increased. Both the storage modulus (G′) and loss modulus (G″) determined by mechanical spectra at 20 °C decreased with decreasing HU. RVA and DSC determinations revealed that lower-HU samples had a lower viscosity in the baking process and a shorter time for starch gelatinization and egg protein denaturation. Observation of the batter density revealed an increasing change, which was reflected by a decrease in the specific volume of final models. TPA showed significant differences in hardness and chewiness, but no significant differences in springiness and cohesiveness were found. CONCLUSION The egg freshness affected the properties of batter systems. © 2015 Society of Chemical Industry

Effects of NaCl concentrations and pH on the intermolecular forces and gel properties of whole chicken egg protein dispersions were studied via solubility, surface hydrophobicity, intermolecular forces, texture analysis, low-field nuclear magnetic resonance (LF-NMR) and colour analysis. Results showed that the intermolecular forces involved in the formation of egg gel were regulated by NaCl/pH. The results of gel fracture analysis suggested that the changes of fracture strength and strain were closely related with the internal balance of gel molecular forces. Moreover, a negative/positive correlation existed in the free water/bound water relaxation proportion and fracture strength. These findings provide an important theoretical basis for the innovation of heat-induced egg gel products.

After formation of the ovalbumin (OVA)-gum arabic (GA) complex coacervates, a more ordered crystal structure was obtained, and the protein denaturation temperature increased from 72 to 96 °C. GA can reduce the pH-induced conformational perturbations of ovalbumin. The presence of GA improved the stability of the α-helix and β-turn regions against pH, but showed less influence on the random coil and β-sheet domains. The complex coacervates showed the highest viscosity value at pH 3.7 compared with the other pH values tested (4.0, 3.4, 3.0, 2.7) due to the stronger interactions of OVA and GA. A large thixotropic loop was observed for the coacervate obtained at pH 3.7 compared with that obtained at pH 4.0. Moreover, the salt concentration and OVA:GA ratio influenced the rheological properties by affecting the structure and composition of the complexes. A stronger interaction between OVA and GA led to greater viscoelastic properties.

The effects of NaOH and NaCl on the rheology and gel properties of hen egg white were investigated. As the concentration of NaOH increased, egg white gel exhibited lower opacity and particle turbidity with coincidental increase in zeta potential, while the addition of NaCl resulted in the formation of opaque egg white gel and increase of surface hydrophobicity, particle turbidity and zeta potential. Rheological tests showed that alkali treatment will affect the unfolding state of egg white proteins during the heat stage while NaCl addition can inhibit the unfolding of egg white proteins. The results of correlation analysis indicated that random coil and α-helix were in good correlation with gel textural properties. Therefore, the rheology and gel properties of alkali/salt-induced egg white dispersions were closely related to the changes in surface hydrophobicity, molecule surface charge, and protein secondary structure.

The aim of the present study was to fabricate catechin-egg white protein (CT-EWP) conjugates as novel food-grade antioxidant emulsifiers designed to improve the physicochemical stability of β-carotene (BC) emulsions. CT-EWP conjugates were synthesized using free radical grafting, and the formation of conjugates was confirmed by electrophoresis and liquid chromatography-mass spectrometry. The physicochemical stability of BC emulsions was characterized by measuring alterations in particle size, ζ-potential and BC retention. The particle size and ζ-potential changed more rapidly at 37°C than at 4 or 25°C, however no creaming or oiling-off were observed at any of the storage temperatures, suggesting all emulsions were physically stable throughout the 30-day storage period. Compared to emulsions stabilized by EWP or CT+EWP physical mixtures (no conjugation), CT-EWP conjugate-stabilized emulsions had better resistance to environmental stresses, such as thermal processing and high ionic strengths, which was attributed to a stronger steric repulsion between the oil droplets. CT-EWP conjugates also significantly reduced the degradation rate of BC in emulsions during storage (p

Effects of the brine solution with different NaOH concentrations on the physicochemical properties, intermolecular forces, and gel properties of duck egg whites were studied. The free alkalinity, salt content and surface hydrophobicity of egg whites increased as the pickling time and NaOH concentration increased. The primary intermolecular forces (disulfide bonds and hydrophobic interactions) in the alkali egg white gels were increased firstly and then decreased, resulting from the fact that the proteins were degraded under strong alkali conditions during the late stage of the pickling process. Changes of hardness and springiness of egg white gels were closely related with the interactions of the protein molecules. Thereinto, the change tendency of springiness was in accordance with the changes of hydrogen bond of egg white gels. The colour of the egg white gels obtained from alkali treatment changed from white to amber during pickling.

Natural biopolymer stabilized oil-in-water emulsions were formulated using ovalbumin (OVA), gum arabic (GA) solutions and their complexes. The influence of interfacial structure of emulsion (OVA-GA bilayer and OVA/GA complexes emulsions) on the physical properties and antimicrobial activity of thyme oil (TO) emulsion against Escherichia coli (E. coli) was evaluated. The results revealed that the two types of emulsions with different oil phase compositions remained stable during a long storage period. The oil phase composition had an appreciable influence on the mean particle diameter and retention of the TO emulsions. The stable emulsion showed a higher minimum inhibitory concentration (MIC), and the TO emulsions showed an improved long-term antimicrobial activity compared to the pure thyme oil, especially complexes emulsion at pH 4.0. These results provided useful information for developing protection and delivery systems for essential oil using biopolymer.