Properties Of Egg White Proteins Research Articles

Lysozyme impacts gel properties of egg white protein via electrostatic interactions, polarity differences, local pH regulation, or as a filler

The effects of lysozyme on egg white gel properties and their underlying causes were investigated under comparison between lysozyme removed with ion exchange resin and three levels of commercial lysozyme powder (1/2, 2/2, 3/2 the natural concentration in egg white) re-added in the lysozyme-removed system. Results showed that a lysozyme-removed gel obtained the best water holding capacity (61.61 %), lowest cooking loss (11.85 %), and enhanced textural properties (hardness, 638.04 g; resilience, 0.57; and gumminess), which was attributed to lysozyme promoting protein aggregation and weakening electrostatic repulsion by charge neutralization and competition for water, and this could be eliminated by removing lysozyme. Besides, the stronger intermolecular interactions (enhanced ionic bonds, hydrogen bonds and inhibited hydrophobic interactions), the shorter transverse relaxation time (T21 and T22), as well as more uniform microstructure formed in the lysozyme-removed gel, allowing the gels to bind more water molecules. With return of lysozyme, the gel properties were weakened to varying degrees, which was also ascribed to the filling of lysozyme in gel matrix narrowed interspace for binding and storage of water. In sum, adjustment on the content of lysozyme can regulate the gel properties of egg white, so as to obtain gels with regulable gel quality and processing characteristics.

Comparison of the effect of hydrodynamic and acoustic cavitations on functional, rheological and structural properties of egg white proteins

The impacts of hydrodynamic cavitation (HC) (orifice plate-2 mm) and acoustic cavitation/ultrasound (US) (probe sonicator- 50% amplitude; 20 kHz frequency) on the functional (foaming, gelling, emulsifying), physicochemical (solubility), rheological and structural properties of egg white proteins (EWP) were evaluated. The egg white solutions were treated for 5, 10 and 15 min for both HC and US. The results suggested that HC-treated samples had higher impact on physiochemical and functional properties when compared to US-treated samples. The best foaming, emulsifying and gelling property was obtained for HC-treated samples (15 min treatment time). Both cavitation treatments exhibited shear thinning behavior, among which US-treated samples had the lowest viscosity. HC-treatment applied for 15 min provided the highest in vitro digestibility (75.51 ± 0.126%) among all the samples. The FTIR spectra of EWP exhibited similar backbone structure for all the samples, while the secondary structure obtained from deconvolution of Amide-I peak differed significantly. Moreover, for product development with EWP, HC -treated samples were more appropriate in gelling and emulsifying applications, which can ensure quality products with higher in vitro digestibility. Overall, this study indicated that HC treatment (for 15 min) improved the functional, rheological, and structural properties of EWP.

Effect of radiofrequency processing on the structural and bio-functional properties of egg white proteins

Radiofrequency (RF) assisted thermal processing can significantly enhance the gel firmness of egg white powder compared to the traditional hot room (HR) processing. Thus, the present study aims to delineate the impact of RF processing on the proteins' structure and bio-functional properties of egg white protein gels. The secondary protein conformations of egg white proteins exhibited no significant alteration upon RF-assisted thermal processing over traditional HR processing. In-vitro gastrointestinal (GI) digestion of egg white gels demonstrated that the RF processing did not compromise the accessibility of digestive proteases despite a more robust gel network. Peptides from the GI digest of egg white gel showed that Ovalbumin and Ovotransferrin were the parent proteins of most of the unique peptides generated, and minor structural differences accounted for these peptides. The bioavailability of the egg protein-derived peptides remains unaffected after RF processing without compromising the viability and integrity of the GI epithelial cells.

Effect of Xanthan Gum, Kappa-Carrageenan, and Guar Gum on the Functional Characteristics of Egg White Liquid and Intermolecular Interaction Mechanism.

This study evaluated the effects of three polysaccharides, xanthan gum (XG), kappa-carrageenan (CA), and guar gum (GG), on the foaming and emulsifying properties of egg white liquid (EWL) and explored the intermolecular interactions and aggregation states in the initial polysaccharide–EWL complex. The results showed that the addition of XG and GG significantly improved the foaming stability of EWL on the one hand, from 66% to 78% and 69%, respectively (p < 0.05). On the other hand, the addition of XG and GG significantly improved the foam uniformity and density, and the average foam area decreased from 0.127 to 0.052 and 0.022 mm2, respectively (p < 0.05). The addition of XG and CA significantly improved the emulsification activity index (from 13.32 to 14.58 and 14.36 m2/mg, respectively, p < 0.05) and the emulsion stability index (from 50.89 to 53.62 and 52.18 min, respectively, p < 0.05), as well as the interfacial protein adsorption at the oil–water interface; it also reduced the creaming index. However, GG negatively affected these indicators. Furthermore, the electrostatic and hydrophobic interactions among molecules in EWL due to XG and the electrostatic, hydrogen bonding, and hydrophobic interactions among molecules in EWL due to CA ultimately led to the irregular aggregation of egg white proteins. Hydrophobic interactions and disulfide bonds between molecules in EWL–containing GG formed filamentous aggregations of egg white proteins. This work reveals that molecules in the polysaccharide–egg white complexes aggregate by interaction forces, which in turn have different effects on the foaming and emulsifying properties of egg white proteins.

Ball-milling is an effective pretreatment of glycosylation modified the foaming and gel properties of egg white protein

In order to further improve the functional properties of egg white protein powder (EWP), the effects of ball-milling pretreatment on the functional properties of EWP by glycosylation modification were studied. The results manifested that glycosylation reaction was successful. Compared with CEWP (glycosylated egg white protein powder without ball-milling pretreatment), BCEWP (glycosylated egg white protein powder after ball-milling pretreatment) showed lower free amino acid content and higher solubility. The results indicated that ball-milling pretreatment changed the secondary and tertiary structures of protein then prominently enhanced the degree of glycosylation reaction of EWP. Foaming ability of BCEWP (203.3%) was 1.12 times higher than that of CEWP (182.2%). The water holding capacity (WHC) of BCEWP (104.77%) was significantly larger than that of CEWP (100.28%), besides, BCEWP had greater gel springiness than CEWP. These results confirmed that ball-milling was an effective pretreatment to enhance the foaming and gel properties of EWP by glycosylation modification. • Ball-milling pretreatment changed the egg white protein (EWP) structure. • The degree of glycosylation reaction of EWP was significantly increased after ball-milling. • Ball-milling is an effective pretreatment of glycosylation modified the foaming properties of EWP. • Ball-milling pretreatment glycosylation prominently improved the gel properties of EWP.

Influence of atmospheric-pressure cold plasma-induced oxidation on the structure and functional properties of egg white protein

This study examined the effects of atmospheric-pressure cold plasma (ACP) on the structure and functional properties of egg white protein (EWP). Egg white solution was treated with ACP for 0, 10, 20, 30, and 40 min. The structural unfolding of EWP was confirmed as the exposed free SH group content and surface hydrophobicity increased during the 30 min treatment; however, 40 min of ACP treatment showed the opposite tendency, suggesting the formation of protein aggregates. The emulsion stability of egg white emulsions was the highest at 30 min but decreased again at 40 min. In addition, the proportion of large droplets decreased as the treatment time increased up to 30 min. As a result, moderate oxidation was induced during 30 min of ACP treatment, which could contribute to the enhancement of functional properties of EWP. However, excessive oxidation caused by further ACP treatment negatively affected the enhanced functional properties. Industrial relevanceEgg whites are used as functional ingredients for a variety of food products, so the quality and functionality of egg whites can directly affect the productivity of the final products. The present study suggests the moderate oxidation of egg white protein induced by atmospheric-pressure cold plasma, which could contribute to the enhancement of functional properties. These applied studies can serve as a cornerstone for the establishment of advanced oxidation techniques that can enhance the functionality of egg whites without chemical additives, and consequently contribute to the improvement of food quality and productivity.

Effect of subcritical water treatment on the structure and foaming properties of egg white protein

The effect of conventional heat treatment and subcritical water (SW) treatment on the structure and foaming properties of egg white protein (EWP) were investigated. Compared with unheated EWP, SW treatment enhanced the foaming capacity by 3-fold and induced the transition from α-helix structure (from 29.8% to 13.6%) to β-sheet structure (from 18.2% to 26.2%) and random coil structures (from 39.7% to 46.3%). Meanwhile, heating at 90 and 120 °C both remarkably increased the surface hydrophobicity and aggregation of EWP. The particle size of EWP (unheated, heated at 90 and 120 °C) was 104.37 nm, 438.5 nm and 311.6 nm, respectively. Combined with the results of sodium dodecyl sulfate-polyacrylamide gel (SDS-PAGE) electrophoresis, we speculated that SW treatment could hydrolyze protein aggregates formed at 90 °C into small molecular weight aggregation. Scanning electron microscopy revealed that SW treatment could induce the surface of EWP rougher, looser and more fragile. The viscosity and surface tension proved that SW treatment could improve the flexibility of EWP. These were all beneficial to the protein adsorption at the air-water interface and enhancement of foaming capacity. It might be of great significance for us to re-recognize the influence of high temperature on the foaming properties of egg white protein.

Tea polyphenols on emulsifying and antioxidant properties of egg white protein at acidic and neutral pH conditions

The influence of tea polyphenol (TP) treatment on the emulsifying, antioxidant and structural properties of egg white protein (EWP) at acidic (pH 3.8) and neutral (pH 7.0) pH conditions were completely evaluated. The emulsifying activity of EWP was significantly improved after TP treated at pH 7.0 (p < 0.05), but it is negatively correlated with TP concentration. TP treatment at pH 7.0 and 3.8 could significantly improve the antioxidant activity of EWP (p < 0.05). TP treated at pH 3.8 could significantly increase the average particle sizes of EWP aggregates, especially at higher TP concentration, thus impair to the emulsifying behavior. The affinity of EWP with TP at pH 7.0 was stronger than that at pH 3.8, thereby reducing the surface hydrophobicity and isoelectric point. In conclusion, the results of this work could provide a theoretical basis for the development of bifunctional nutrients with both antioxidant and emulsifying properties.

Triacylglycerides and Phospholipids from Egg Yolk Differently Influence the Immunostimulating Properties of Egg White Proteins.

As part of a whole egg, egg white proteins are embedded in a lipid matrix that could modify their presentation to the immune system and their allergenic properties. The present study examines the impact of the main egg lipid components, triacylglycerides and phospholipids, in the early events of sensitization to egg. To this end, BALB/c mice were exposed intragastrically to egg lipids and egg lipid fractions, alone and in mixtures with egg white proteins, and Th2-promoting and proinflammatory effects were investigated. Our results highlight that the egg lipid fraction is responsible for Th2 adjuvant effects and point at a different influence of triacylglycerides and phospholipids on the bioavailability and immunomodulating properties of egg white proteins. While triacylglycerides promote type 2 responses at the small intestine level, phospholipids reduce the solubility of EW proteins and induce Th2 skewing in lymphoid intestinal tissues, which may have a direct impact on the development of egg allergy.

Foaming properties and aggregation mechanism of egg white protein with different physical treatments

In this work, we studied foaming properties of egg white protein (EWP) under different physical modifications induced by supercritical carbon dioxide (SCCD), ultrasound, heat or high-pressure homogenization. Formation mechanisms of EWP aggregates and the relationships between processing parameters were discussed. Results showed that the maximum FC values were obtained via treatment with SCCD at 9 MPa (107.7%), ultrasound at 360 W (96.5%), heating at 45 °C (105%) and homogeneous pressure under 600 bar (87%), which were all dramatically higher than that of the control (29.9%). However, not all EWP treatments were conducive to the maintenance of foaming stability (FS). Results also indicated a close relationship between foaming properties and protein aggregation. Ovomucin in EWP might dissociate into small fragments or form new aggregates following treatment with SCCD, ultrasound or high-pressure homogenization, which caused a more dispersed particle size and decreased viscosity of EWP. Heating treatment greatly enhanced the viscosity of EWP, which was attributed to the irreversible destruction of the protein structure. Additionally, it seemed that SCCD maximally increased the FC of egg white through the synergy of selected pH and pressure treatments. Overall, using different physical treatments, it is possible to produce EWP with good foaming properties.

Molecular structural modification of egg white protein by pH-shifting for improving emulsifying capacity and stability

The effect of pH-shifting on the molecular structure and emulsifying properties of egg white protein (EWP) was investigated. EWP was subjected to extreme alkaline pH treatment (11, 11.5, 12, 12.5, and 13) and then adjusted to neutral (pH 7.0). The results showed that the emulsifying activity and emulsion stability of EWP were enhanced under pH-shifting, especially at pH 13. The surface hydrophobicity of EWP13 increased significantly from 306.94 to 11653.67 (p < 0.05), and the free sulfhydryl content of EWP13 increased significantly from 15.106 μmol/g to 121.86 μmol/g (p < 0.05). Also, the size and turbidity of EWP13 were minimal, producing EWP soluble aggregates with an average size of 52.90 nm (p < 0.05). Moreover, circular dichroism (CD) and intrinsic fluorescence spectra showed that the secondary and tertiary structures changed. At EWP12.5 and EWP13, it showed a decrease of α-helix and an increase of β-sheet. The intrinsic fluorescence spectra suggested that Phe, Tyr, and Trp were exposed to a polar environment due to EWP unfolding. In conclusion, the EWP structure was changed by pH-shifting, resulting in more exposed hydrophobic groups, thus increasing the emulsion stability. Correspondingly, the emulsion of EWP13 showed the best stability under the conditions of oxidation, heating, and salt than native EWP. This work may provide an effective method and theoretical basis for molecular modification to improve the functional properties of EWP by pH-shifting treatment.

Mild heating assisted alkaline pH shifting modify the egg white protein: The mechanism and the enhancement of emulsifying properties

Mild heating (20 °C, 40 °C, 60 °C, and 80 °C) for 1 h assisted pH12 shifting on the structural, physicochemical and functional properties of egg white protein (EWP) were investigated. The results of intrinsic fluorescence, surface hydrophobicity, and free sulfhydryl groups indicated that the tertiary structure depolymerized, the hydrophobic groups exposed and the protein subunits dissociated. Fourier transform infrared spectrophotometer and circular dichroism showed that the content of α-helix decreased, and the content of β-turn increased in the secondary structure of EWP. Moreover, the size and zeta potential of EWP12-80 significantly decreased to 119.17 nm (P < 0.05) and −32.53 mV (P < 0.05), and the solution of EWP12-80 was clear and translucent. In terms of emulsification, the emulsion formed from the modified EWP maintained excellent stability in particle size and distribution. Correspondingly, compared with the untreated EWP, the emulsions formed by the modified proteins also had a uniform and stable particle size under the conditions of heating and salt. Therefore, pH12 combined with heating to modify EWP may be an ideal method to improve its functional properties, thereby expanding its use in the food industry.

Effect of polysaccharides on the functional properties of egg white protein: A review.

Egg white protein (EWP) was one of the high-quality protein sources and widely used in the food industries because of excellent emulsifying, gelling, and foaming properties. Polysaccharides as a natural biological macromolecule have been used to improve the functional properties of EWP. The electrostatic interaction was the main driving force between EWP and polysaccharides. However, protein-polysaccharides complexes were susceptible to environmental factors including pH, ionic strength, polymer ratio, and temperature. In this paper, the functional properties of EWP were summarized. More importantly, the effects of polysaccharides on the functional properties of EWP were highlighted and reviewed referring to emulsifying, foaming, and gelling properties. The impact of environmental factors on the protein-polysaccharides interaction were also discussed. This paper leaded to enrich research systems of protein-polysaccharides interaction and provided information for the development of new egg white-derived foods.

Effect of preparation procedure on properties of egg white protein and the fibrous microparticle stabilized complex emulsions.

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.

Mechanism of enhancing foaming properties of egg white by super critical carbon dioxide treatment

The effect of supercritical carbon dioxide (SCCD) treatment at varying processing time (30–90 min) on foaming and structure properties of egg white protein (EWP) were studied in this paper. The highest foaming ability (107.7%) was obtained after 60 min SCCD treatment, which was 3.6-fold to the control group. Foaming stability kept stable under the processing time of 75 min. Results of surface tension, surface hydrophobicity, rheological properties and particle size indicated that protein was easier to spread to the gas-liquid interface and generate molecular rearrangement. Circular dichroism (CD) and Endogenous fluorescence spectrum showed that there were slight changes on the secondary structure of EWP. The α-helical structure of the protein was destroyed and the particle size became uneven, which indicated that the protein structure became more flexible and loose. The results of this study indicate that SCCD treatment had a potential to be implemented to enhance foaming properties of EWP.

Structural and functional properties of hydrolyzed/glycosylated ovalbumin under spray drying and microwave freeze drying

Ovalbumin (OVA), the main protein in egg white, affects most of the functional properties of egg white protein in food processing. The aim of this study was to investigate the effects of spray drying (SD) and microwave freeze drying (MFD) on the preparation of hydrolyzed/glycosylated ovalbumin (HGOVA) and provide useful information on the applications of egg protein powders in the food industry. Results demonstrated that the structure of HGOVA was considerably changed, and its functional properties were improved compared with those of native OVA. SD and MFD processing did not lead to dissociation of HGOVA subunits. SD-HGOVA exhibited higher protein solubility, emulsifying activity, foaming capacities, and gel hardness than MFD-HGOVA. However, MFD-HGOVA was better than the SD-HGOVA in terms of color, emulsion stability, foam stability, water/oil absorption capacity, and thermal stability. Selection of an appropriate drying method could enhance the potential applications of HGOVA in the food industry.

Effect of different doses of Co-60 gamma-ray irradiation treatment on the micro-rheological and emulsifying properties of liquid egg white

This study investigated the effects of different irradiation doses (0kGy, 1kGy, 3kGy, 5kGy) on the structural and emulsifying properties of egg white protein by studying the egg white protein emulsion particle size, zeta potential, emulsion droplet microstructure, emulsification index, interfacial tension, secondary structure, micro-rheological properties. The results show that after irradiation treatment, the average particle size of the emulsion was significantly (p < 0.05) reduced, and the zeta potential value was significantly (p < 0.05) increased. As the irradiation dose increased, the interfacial tension between the oil phase and the water phase decreased, and the two-phase separation time of the emulsion is significantly (p < 0.05) prolonged. The content of α-helix and β-sheet of the protein was significantly (p < 0.05) decreased, while the content of β-turn and random coil was significant (p < 0.05) increased. In the microstructure of the emulsion droplets, the dispersion of the emulsion droplets after irradiation was improved, and the observed droplet size was significantly reduced. In terms of rheological properties, the fluidity of the egg white protein emulsion droplets increased. The elasticity and viscosity of the egg white protein emulsion decreased. All these results suggested that irradiation treatment can improve the emulsification characteristics and stability of egg white protein.

Dietary glycerol monolaurate supplementation for the modification of functional properties of egg white protein.

Understanding the interactions between feed additives and the functional properties of egg white protein (EWP) may offer novel insights into the effects of feed additives on laying hens and may provide an alternative for modification of the functional properties of EWP by using laying hens as bioreactors. Glycerol monolaurate (GML) is widely used in the food industry as an effective antibacterial emulsifier. In this work, the effects of three doses of dietary GML supplementation (150, 300, and 450 mg kg-1 hen) on the functional properties of EWP were investigated. The hardness of EWP gels was significantly improved by 300 and 450 mg kg-1 GML supplementation. Foaming capacity (FC) and foaming stability (FS) were increased after GML treatment; 450 mg kg-1 GML supplementation showed the most significant improvements, with 44.82% in FC and 23.39% in FS. Stabilization of EWP-oil emulsions was also improved, supported by a slowed creaming process and the formation of smaller oil droplets. The heat denaturation temperature and rheological properties were also modified by dietary GML supplementation, implying improved thermal stability. Our study demonstrated that GML supplementation has the potential to modify the functional properties of EWP, broadening the application of GML and providing a new perspective for evaluation of the efficacy of feed additives. © 2019 Society of Chemical Industry.

Effect of free radical-induced aggregation on physicochemical and interface-related functionality of egg white protein

This study investigated the impact of free radical-induced aggregation by a redox pair (ascorbic acid + H2O2) on physicochemical characteristics, structure, and rheology as well as the emulsifying and foaming capacity of egg white protein (EWP). In general, this treatment led to oxidize the free SH groups, a little change in secondary structure, increasing surface hydrophobic (H0) and ζ-potential as well induce aggregation of egg white protein through disulfide cross-linking. The pH at which the oxidative aggregation reaction was performed had a significant effect on the functionality of the EWP. The EWP aggregated at pH 11 had a very high apparent viscosity, which justified by its greater H0, higher aggregation yield and larger aggregates with high effective volume, as confirmed by SDS-PAGE and AFM. Furthermore, emulsions prepared by aggregated EWP samples, particularly the EWP aggregated at pH 11, showed higher stability against droplet flocculation and phase separation during storage for 30 days at various pH (4–7) and salt concentration (0–200 mM) as compared to emulsions made with native EWP, presumably due to create a more viscoelastic film with promoted steric hindrance on oil droplets. Moreover, a dramatically enhanced foam stability was obtained by the EWP aggregated at pH 11. This study suggested that radical induced aggregation has a potential to improve the interface-related properties of egg white protein.

Improving Emulsifying Properties of Egg White Protein by Partial Hydrolysis Combined with Heat Treatment

The present study investigated proteolysis combined with heat treatment to make hen Egg White (EW) an efficient emulsifier. EW was hydrolyzed by protease (Thermoase®) at various Enzyme Concentrations (EC) (w/w, 0.1%, 0.2%, 0.4%, 0.8%), followed by heating at 90°C for 8 min. Results showed that optimal emulsifying ability and stability, determined by measurement of emulsion turbidity, were obtained when EC was 0.4%, followed by heat treatment at 90°C. The hydrolysate thus prepared had higher emulsifying ability and stability than either native egg white (nEW) or small molecular weight EW peptides (Runpep®), close to the properties of Egg Yolk (EY) which was a reference as a food emulsifier. Surface hydrophobicity (H0) was found to be linearly related to the emulsifying activity and stability of hydrolyzed egg white proteins.