Egg White Gel Research Articles

The effect of pH, sucrose, salt and hydrocolloid gums on the gelling properties and water holding capacity of egg white gel

The aim of this investigation was to evaluate the effect of pH variation, sucrose, salt and hydrocolloid gums (xanthan, guar, karaya and locust bean) addition on the gelling properties and the water holding capacity (WHC) of the egg white (EW) gel. Tree levels of pH (4.5, 6.5, 8.0), sucrose/salt (1, 3, 6% w/w) and hydrocolloids (0.01%, 0.10%, 0.20% w/w) were tested in this study. Obtained results showed that mechanical properties and WHC of the EW gel were decreased significantly by pH variation. Addition of salt and sugar improved firmness and elasticity of the EW gel. However, the presence of salt decreased the WHC of the gel. Whereas, in the presence of sugar, WHC was slightly improved. The presence of hydrocolloids in EW gel is associated with the modification of the functional properties of the EW proteins. Xanthan gum decreased hardness and strength and increased WHC of the gel to 97.18% at 0.2%. Guar and karaya gums increased mechanical properties of EW gel at the lowest concentration (0.01%). Locust bean gum was shown to enhance texture profile of EW gel at all tested levels. WHC was significantly improved in the presence of food gums. Microstructure observations of EW gels were also carried out by environmental scanning electron microscopy.

Novel egg white gel polymer electrolyte and a green solid-state supercapacitor derived from the egg and rice waste

Herein, we fabricate a novel egg white gel polymer electrolyte and green solid-state supercapacitor for the first time, by utilizing broken eggshell and rice husks, the biomaterials of egg and rice waste. Taking advantages of the high affinity between the egg white and eggshell membranes and the optimization of electrolyte salt, the fabricated novel egg white gel polymer electrolyte combines several advantages such as high ionic conductivity, high electrolyte retention, adequate mechanical properties and thermal stability, and environmental friendliness. Furthermore, profit from the significantly electrolyte retention and improved contact between EW-GPE and the rice husk based activated carbon electrodes, the resulting green solid-state supercapacitor exhibits high flexibility, good electrochemical properties (i.e., high specific capacitance of 214.3 F g−1 at 0.2 A g−1 and 204.4 F g−1 at 1 A g−1) and stable cycle performance. In addition, the present investigation of a green gel polymer electrolyte and solid-state supercapacitor opens new avenues towards using low-cost daily waste biomaterials in new energy storage devices.

Combination effects of NaOH and NaCl on the rheology and gel characteristics of hen egg white proteins

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.

Characteristics of gelling and water holding properties of hen egg white/yolk gel with NaCl addition

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.

Effects of copper ions on the characteristics of egg white gel induced by strong alkali

This study investigated the effects of copper ions on egg white (EW) gel induced by strong alkali. Changes in gel characteristics were examined through texture profile analysis, scanning electron microscopy (SEM), and chemical methods. The value of gel strength reached its maximum when 0.1% copper ions was added. However, the lowest cohesiveness values were observed at 0.1%. The springiness of gel without copper ions was significantly greater than the gel with copper ions added. SEM results illustrated that the low concentration of copper ions contributes to a dense and uniform gel network, and an open matrix was formed at 0.4%. The free and total sulphhydryl group content in the egg white protein gel significantly decreased with the increased copper. The increase of copper ions left the contents of ionic and hydrogen bonds basically unchanged, hydrophobic interaction presented an increasing trend, and the disulfide bond exhibited a completely opposite change. The change of surface hydrophobicity proved that the main binding force of copper induced gel was hydrophobic interaction. However, copper ions had no effect on the protein component of the gels. Generally, a low level of copper ions facilitates protein–protein association, which is involved in the characteristics of gels. Instead, high ionic strength had a negative effect on gels induced by strong alkali.

Improved rheological properties of chicken egg frozen gels fortified by ᴅ-ketohexoses

The aim of this study was to examine the rheological properties of chicken egg gels containing 10% ᴅ-ketohexose (ᴅ-fructose, ᴅ-allulose, ᴅ-tagatose, and ᴅ-sorbose) and to compare the effects of ketohexoses on freeze-thawing of egg gels with ᴅ-glucose (Glc), sucrose (Suc), and trehalose (Tre). In both whole egg (WE) and egg white (EW) gels, ketohexose-gels had higher breaking stress than Glc-, Suc-, and Tre-gel (WE gels, 15.6–35.3%; EW gels, 7.6–26.1%). The ketohexose-gels of WE showed similar viscoelastic properties and water-holding capacity to Glc-, Suc-, and Tre-gel. Ketohexose-gels of EW possessed higher viscosity and higher water-holding capacity than the other sugar-gels. Ketohexoses more effectively suppressed the syneresis and physical properties of egg gels by freeze-thawing than Glc, Suc, and Tre did. The application of ketohexoses to egg gel products can improve the quality of frozen foods that contain egg gels. Practical applications Sugar is extensively used for producing egg-based gel products because sugar contributes to the stabilization of food structure and adds sweetness. Sugar also prevents deterioration of the physical properties of frozen foods from freezing and thawing. Interest in the rare ketohexoses ᴅ-allulose (Alu) and ᴅ-tagatose (Tag) is growing in food industry, because Alu and Tag have some health benefits, such as prevention of postprandial blood glucose level and suppression of adiposity. The utilization of rare ketohexoses as food ingredients should improve the rheological and functional properties of food products, including those of frozen foods.

Fabrication, characterization and controlled release properties of oat protein gels with percolating structure induced by cold gelation

Cold-set oat protein isolate (OPI) gels possessing a percolating network structure were successfully prepared using a glucono-δ-lactone (GDL) induced acidification method. The polymer-like percolating structures were established by active OPI monomers as small building block units through abundant cross-linking points. By increasing the GDL concentration, more intra-floc linkages and greater particle volume fractions were created at the supramolecular level, resulting in a dense rough gel wall with superior mechanical properties. In particular, at a 10% GDL content the gel was generated at the OPI isoelectric point (IEP). This OPI gel had a compact network structure with small pores and a thick wall, with an excellent water holding capacity (90%) and comparable mechanical strength (30 kPa) to egg white gel (22–32 kPa). Also, the cold-set OPI gels could resist acidic juice and pepsin digestion, which protected both α-amylase enzyme activity and the viability of probiotics in harsh gastric conditions. The in vitro release experiment demonstrated that OPI gels had the capacity to prevent the premature release of bioactive compounds in simulated gastric fluids, and yet still allowed their gradual release in a simulated intestinal environment where they normally would be absorbed. A convenient and non-toxic method to prepare OPI gels with superior performance has been described. These gels have the potential to act as delivery vehicles for sensitive compounds in food and non-food applications.

Effect of Proteolytic Modification on Texture and Mastication of Heat-Treated Egg White Gels

Raw egg white undergoes sol–gel transition by heat treatment, which changes it to an elastic gel. Here, protease treatment to render a new texture to heated egg white gel was applied. Protease‐treated gels exhibited ductile flow without obvious rupture points. Transmission electron microscopy analysis showed that in protease‐treated gels, protein aggregates were distributed more homogeneously compared with that observed in the untreated control, probably because ovalbumin was digested into small peptides as revealed by SDS‐PAGE. The properties of the gel were evaluated by sensory tests and by measuring the movement of the masseter muscle, using surface electromyography. Results showed that maximum bite force and mastication duration were decreased for the protease‐treated gels, which were evaluated as being softer, smoother, less elastic and better textured. Overall, our results indicate that protease‐treated egg white gel has superior qualities and is easier to swallow than the untreated gel.Practical ApplicationsIn the food industry, the use of egg white is limited compared with that of egg yolk and whole eggs. In this study, we performed protease treatment to generate a new food material with smoother and softer texture compared with heat treated egg white. Our findings may expand the consumption of egg white, which can be consumed by people with mastication and swallowing disorders, and reduce the waste of egg white as a surplus product.

Water Holding as Determinant for the Elastically Stored Energy in Protein-Based Gels.

To evaluate the importance of the water holding capacity for the elastically stored energy of protein gels, a range of gels were created from proteins from different origin (plant: pea and soy proteins, and animal: whey, blood plasma, egg white proteins, and ovalbumin) varying in network morphology set by the protein concentration, pH, ionic strength, or the presence of specific ions. The results showed that the observed positive and linear relation between water holding (WH) and elastically stored energy (RE) is generic for globular protein gels studied. The slopes of this relation are comparable for all globular protein gels (except for soy protein gels) whereas the intercept is close to 0 for most of the systems except for ovalbumin and egg white gels. The slope and intercept obtained allows one to predict the impact of tuning WH, by gel morphology or network stiffness, on the mechanical deformation of the protein-based gel. Addition of charged polysaccharides to a protein system leads to a deviation from the linear relation between WH and RE and this deviation coincides with a change in phase behavior.

Changes of microstructure characteristics and intermolecular interactions of preserved egg white gel during pickling

Changes in gel microstructure characteristics and in intermolecular interactions of preserved egg whites during pickling were investigated. Spin–spin relaxation times of preserved egg whites significantly decreased in the first 8days and remained unchanged after the 16th day. SEM images revealed a three-dimensional gel network, interwoven with a loose linear fibrous mesh structure. The protein gel mesh structure became more regular, smaller, and compacted with pickling time. Free sulfhydryl contents in the egg whites increased significantly, while total sulfhydryl contents dramatically decreased during pickling. The primary intermolecular forces in the preserved egg white gels were ionic and disulfide bonds. Secondary forces included hydrophobic interaction and relatively few hydrogen bonds. During the first 8days, the proportion of ionic bonds sharply decreased, and that of disulfide bonds increased over the first 24days.

Investigating the impact of egg white gel structure on peptide kinetics profile during in vitro digestion

This study aimed to explore how food structure, in the form of different egg white gel matrices, impacts the peptide kinetics profiles using an in vitro model that simulated digestion in the adult gastrointestinal tract. Four different gel matrices were prepared by heating egg white gel solutions using different combinations of pH and ionic strength. Label-free quantitative peptidomics and statistical analysis of the resulting kinetics profiles were performed. The 3231 identified peptides were distributed in 7 clusters based on “Gel structure×Digestion time” interaction coefficients, indicating that peptide kinetics profiles were greatly influenced by the gel structure. Moreover, the protein within the gel from which the peptides were released was highly significantly correlated with the peptide clusters, demonstrating that the influence of the gel structure varied according to the protein in question. Such findings may have nutritional relevance in vivo as they imply that the peptides reaching the intestine are different according to the initial EW gel structure.

New controlled release material: aerated egg white gels induced by calcium ions

The aim of the research was to use low-mineral egg white albumin isolate to obtain aerated calcium ion-induced gels and to investigate their aptitude as matrices for active ingredients release. Aerated gels were prepared by adding calcium ions to pre-heated protein dispersions with simultaneous aeration. 20 mM calcium concentration was an optimal concentration at which the maximum viscosity and hardness of the gels were found. For higher concentrations of calcium ions (25–30 mM), aerated gels were characterized by lower values of the moduli and tangent of the phase angle was larger for aerated gels which indicated more viscous character than that of non-aerated gels. Increased ions concentration causes higher aggregation of protein matrix and less smooth microstructure of the interface between the gel and air. An increase in calcium concentration from 5 to 30 mM caused an increase in an average bubble size. The release of calcium ions from aerated gels was measured in an artificial stomach. It occurred by Fickian diffusion through the swelling matrix and it was faster for the gels with higher concentration of calcium. An increase in calcium concentration caused an increase in surface roughness of the aerated gels. There were linear correlations between the quadratic mean of the surface roughness and “n” coefficient from the Ritger and Peppas equation and between the maximum roughness size and “n”. The increased calcium concentration made the gel microstructure more particulate and the surface rougher, which enabled faster proteolysis of the gel in an artificial stomach and faster diffusion of calcium ions.

Dissolution and swelling of soy protein isolate hydrogels in alkali

The chemical dissolution of protein hydrogels, in particular the rate limiting mechanism, differs in the only two systems studied, whey and egg white proteins. With the aim to develop mechanisms general to globular protein networks, we study here the dissolution of soy protein isolate (SPI) hydrogels for the first time. SPI gels dissolve in alkali in a similar manner than egg white gels, but much faster, showing traits expected when the cleavage of interprotein disulfide crosslinks is rate limiting. SPI dissolution is reduced when swelling is inhibited by the addition of salts, although less profoundly than in whey protein gels. Equilibrium swelling experiments of SPI gels show a sudden increase at pH ≥ 11.5, which cannot be predicted from the swelling data at lower pH. Dissolution is evident in swollen SPI gels at pH > 12 but only at low salt concentrations. A double dissolution threshold is therefore also observed like in β-lactoglobulin gels, although its origin is different. The pH threshold in whey proteins at pH ∼11.5 is due to the destruction of non-covalent interactions, but in SPI it only causes a large increase in swelling. Dissolution only occurs at higher alkali concentrations where disulfide crosslinks start to be cleaved quickly. The importance of this reaction in SPI gels, where disulfide crosslinks are not extensive in the gel network, is explained by the large size of most soy proteins that will not detach meanwhile a gel network still exists. The size of the initial proteins becomes a new parameter when analyzing the dissolution of different protein systems, in addition to the chemistry involved in the formation of hydrogels.

Swelling of whey and egg white protein hydrogels with stranded and particulate microstructures

Swelling of protein hydrogels in alkaline conditions strongly depends on the gel microstructure. Stranded transparent gels swell as predicted using a modified Flory–Rehner model with the net protein charge. Particulate opaque gels swell very differently, with a sudden increase at a narrow pH range. Its swelling is not controlled by the protein charge, but by the destruction of the non-covalent interactions. Comparable dissolution thresholds, one with pH and another with the degree of swelling, are observed in both types of microstructures. These conclusions are valid for both whey protein isolate (WPI) gels and egg white gels, suggesting that they are universal for all globular proteins that can form such microscructures. Differences are observed, however, from the prevalent chemical crosslinks in each protein system. Non-covalent interactions dominate WPI gels; when such interactions are destroyed at pH≥11.5 the gels swell extensively and eventually dissolve. In egg white gels, the higher degree of disulphide crosslinking allows extensive swelling when non-covalent interactions are destroyed, but dissolution only occurs at pH≥13 when covalent crosslinks are cleaved. The current study highlights that the microstructure of protein hydrogels, a unique particularity of protein systems compared to other synthetic hydrogels, defines swelling.

The structural properties of egg white gels impact the extent of in vitro protein digestion and the nature of peptides generated

The impact of egg white gel (EWG) structure on the process of digestion was investigated using an in vitro digestion model and a multi-scale characterization of the EWG structure. Four different structures of EWG were prepared combining various pH and ionic strength conditions before heating. The extent of digestion, estimated by the appearance of soluble peptides, was greater for the particulate gel comprising spherical aggregates as compared to the filamentous gel comprising linear aggregates. This result may be explained by an alteration of enzyme diffusion due to the microstructural characteristics of the gel, or an alteration of digestive enzyme adsorption or catalytic activity due to local differences in pH within the gel matrices. Peptide identification using LC-MS/MS highlighted that the aggregate morphology modulated ovotransferrin hydrolysis which resulted in the release of specific peptides depending on the EWG structure. This work illustrates the links existing between two multi-step processes, protein structuration into gel matrices and matrix destructuration by digestive enzymes. Such quantitative and qualitative differences reinforce the importance of the food matrix on the digestibility of food and its subsequent nutritional quality.

Development of a new product: egg white albumen gels with differentiated magnesium release

Commercial egg white isolates (EWI) or concentrates contain substantial quantities of minerals and they easily form heat-induced gels. An innovative, low mineral EWI was used in the present research to investigate the influence of magnesium ions on the gelation process and on the release of these ions in simulated gastric conditions. Heat-induced gelation of egg white proteins was monitored by using an ultrasound viscometer and an oscillatory rheometer. Samples behaved as weak gels with the storage modulus about 5 times larger than the loss modulus. Both methods revealed two phases of gelation. More elastic behavior of gels with an increased magnesium ion concentration can be explained by a higher number of bonds between protein molecules observed in transmission electron microscopy images. An increased concentration of magnesium ions in gel caused an increased release rate of these ions in simulated gastric conditions, which was probably caused by a higher surface roughness of the gel. Higher roughness of the gel surface enlarges the contact area and enables faster hydrolysis. The egg white isolate gels with a high bioavailability organic form of magnesium could be used as food supplement with a regulated magnesium release rate in the human stomach.

Cleaning beyond whey protein gels: Egg white

There has been extensive research in the last decade trying to understand the fundamentals of dissolution of whey protein gels in order to lay the foundations of proteinaceous cleaning processes. To date, experimental data has been limited to whey proteins, raising questions of the applicability of the theoretical frameworks developed for whey proteins to other protein systems. In this work the dissolution of crude egg white gels is studied, which are rich in ovalbumin protein, and which have recently shown a different cleaning behavior to whey deposits. Egg white gels made in well-defined conditions were dissolved in a wide range of alkali and sodium chloride concentrations, and temperature. The dissolution rate was found to increase linearly with the alkali concentration up to 1M, hence confirming the absence of an optimum cleaning concentration observed in whey protein cleaning studies. The apparent activation energy of dissolution for particulate egg white gels was 70–80kJmol−1, suggesting that the dissolution of egg white gels is controlled by the β-elimination of disulfide bonds. Dissolution experiments with salts at different temperatures confirmed that swelling is very important in the dissolution of whey protein gels, but not in egg white gels.

Comparative assessment of dynamic oscillatory measurements on network development and mechanical spectra of gelatine or gellan in maize starch–egg white composite gels

Single component gels (SCG) were formed from gelatine (Glt), gellan (Gll), maize starch (MS) or egg white (EW), while binary component gels (BCG) and tertiary component gels (TCG) were formed by mixing Glt or Gll with MS or/and EW. All gels were evaluated by dynamic oscillatory test. Each type of SCG exhibited distinct network formation profiles. The effects of Glt or Gll proportions on the network formation profiles of BCG and TCG were investigated using mixture design experiments. Glt and Gll yielded composite gels that were remarkably different in terms of network formation profiles. In all [MS:Glt/Gll]-BCG and TCG systems, the network structures were developed during cooling suggesting that Glt and Gll being the main components contributing to network formation. However, for [EW:Glt/Gll]-BCG, component with higher ratios governed the gelling mechanism, while the component with lower proportions acted as an inactive filler within the network.

One step procedure for desalting salty egg white and preparing fat analogue and its application in mayonnaise

In this work, a simple and economical way to desalt salty egg white and prepare fat analogue was developed. Moreover, Desalination of salty egg white and preparation of fat analogue was realized at the same time. The optimal technology for obtaining fat analogue was: egg white concentration of 6%, pH of 4.9, heating temperature of 90 °C and milling time of 15 min. Then application of micrometre-scale egg white gel as fat analogue in mayonnaise was studied. Fat was partially substituted by micrometre-scale egg white gel at levels of 10%, 20%, 30%, 40%, which were referred to S10, S20, S30, S40, respectively, while the full fat (S0) mayonnaise without egg white gel substitution was used as the control experiment. The effects of substitution ratio on mayonnaise was determined by rheology measurements, colour measurements, optical microscope observation and caloric values analysis, which indicated that fat in mayonnaise substituted with egg white gel of not more than 30% was acceptable. Meanwhile, the product has good storage stability in a certain storage period. This study shows good potential for micronized desalted egg white gel to be used as fat analogue in mayonnaise.

Changes in gel characteristics of egg white under strong alkali treatment

Changes in gel characteristics, such as rheological and textural properties, microstructures, and intermolecular forces, of egg white (EW) treated with strong alkaline solution were investigated. The viscosity of EW increased gradually in the pre-gel phase. After the gel was formed, the textural properties and microstructures became dynamically changeful. With continuous strong alkali treatment, the formed gel was destroyed and gradually collapsed. Changes in sulfhydryl (SH) group and disulfide (SS) bond contents suggested that oxidation and SH–SS bond exchange reactions rapidly occurred under strong alkali conditions. However, SS bonds were easily broken at very high pH. Selective protein solubility of EW gels indicated that more than half of the total bonds were ionic. Furthermore, one third bonds were SS. Approximately 10% of these bonds was hydrophobic interactions, and few hydrogen bonds were present. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles revealed that the proteins in the gel were degraded and aggregated by alkali treatment. Hence, ovalbumin was involved in the cross-linking of SS bonds rapidly promoted by alkali treatment, and also implicated in gel formation supported by various intermolecular forces, such as ionic bond and hydrophobic interactions.