Ovalbumin Gels Research Articles

Role of Amyloid Type Cross β-Structure in the Formation of Soluble Aggregate and Gel in Heat-Induced Ovalbumin

The heat-induced denaturation curve of ovalbumin followed by the ellipticity at 222 nm in circular dichroism spectra was consistent with that monitored by fluorescence with thioflavin T, which is an indication of amyloid fibril formation, while other proteins such as lysozyme and ovotransferrin did not fluoresce with thioflavin T during heat denaturation. The amount of soluble aggregate formed during heat denaturation was proportional to the increase in fluorescence with thioflavin T. The binding of soluble aggregates with thioflavin T was greatly suppressed in heat-denatured ovalbumin in the presence of thioflavin T. The similar inhibition effect of thioflavin T on the gel formation of heat-induced ovalbumin was observed. These results suggest that the amyloidogenic intermolecular beta-structure is involved in the formation of soluble aggregate and gel of heat-induced ovalbumin.

Light Scattering Study of Heat-Induced Aggregation and Gelation of Ovalbumin

The effect of ionic strength on the interaction of ovalbumin, a globular egg white protein, in aqueous solution was investigated using static and dynamic light scattering. Strong repulsive interact...

Rheology and structure of ovalbumin gels at low pH and low ionic strength

The objective of this study was to relate the rheological behavior of ovalbumin gels at low pH and low ionic strength to their mesoscopic structure, using rheological measurements and Transmission Electron Microscopy (TEM). Varying pH, ionic strength and protein concentration, we obtained transparent solutions, transparent gels, opaque gels, or turbid gels, upon heating and subsequent cooling of the ovalbumin solutions. At equal pH and increasing salt concentration we found an increase in turbidity, suggesting that the structure of the aggregates changed from linear or branched to more clustered aggregates. The gel strength increased with increasing salt concentration. A similar trend was observed at equal ionic strength and increasing pH. TEM micrographs of ovalbumin aggregates at pH 2 and 15 mM NaCl show that the ovalbumin aggregates are linear. Increasing the pH from 2 to 3.5 results in structures that are still linear, but with a higher degree of clustering. No random aggregates were observed. TEM micrographs of the gel phase at pH 3.5 and 30 mM NaCl (turbid) show that the structure consists of linear aggregates organized in large clusters of approximately 230–350 nm. At pH 2 and 30 mM NaCl (transparent) the gel consists of single strands with a diameter of about 3.3–3.9 nm, i.e. one or at most two monomers thick.

Isotropic Force Percolation in Protein Gels

We have determined elasticity data of various ovalbumin gels as a function of concentration of ovalbumin and analyzed these data in terms of a percolation model. In addition, we have analyzed elasticity data of a multitude of other protein gels. We find that all data can be described by one percolation model. The critical exponent is 1.79 ± 0.25, in accordance with isotropic percolation. The value of the critical percolation threshold varies by an order of magnitude. The findings suggest that the effects of external fields on gelation can be captured by the effects of these external fields on the critical percolation threshold.

DISODIUM CROMOGLYCATE INHIBITS PRODUCTION OF IMMUNOGLOBULIN E

Disodium cromoglycate (DSCG) has been shown to inhibit therelease of mediators from mast cells. In the present study, the effect ofDSCG on active anaphylactic reaction was studied in mice. DSCG dose-dependentlyinhibited the active systemic anaphylactic reaction and serum immunoglobulin(Ig)E production induced by immunization with ovalbumin, Bordetellapertussis toxin and aluminum hydroxide gel. DSCG strongly inhibitedIL-4-dependent IgE production by lipopolysaccharide-stimulated murine wholespleen cells. In the case of U266 human IgE-bearing B cells, DSCG also showedan inhibitory effect on the IgE production. These results suggest that DSCGhas an anti-anaphylactic activity by inhibition of IgE production from B cells.

A Cryo-TEM Study of Protein–Surfactant Gels and Solutions

Oppositely charged globular protein and surfactant systems, such as lysozyme–sodium dodecyl sulfate (SDS) and ovalbumin–dodecyltrimethylammonium chloride (DOTAC) form precipitate, gel, and colorless solution in water over a wide concentration range. Bluish solutions are also recognized in connection with the redissolution of precipitate as well as prior to the gel formation. For the lysozyme–SDS system the bluish solution has been suggested to consist of finely dispersed gel particles in solution. The oppositely charged bovine serum albumin (BSA)–DOTAC–water system forms only a large, clear solution phase and a narrow, bluish solution region within a very limited surfactant concentration range. In the lysozyme–SDS system the formation of protein–surfactant aggregates and their growth and breakdown are studied in detail by cryogenic-transmission electron microscopy (cryo-TEM) method. In particular a series of samples with an increased surfactant concentration at fixed 4 wt% of lysozyme is studied. Imaging of the bluish solution at different protein concentrations exhibits large aggregates in the form of rod-like, sheet-like, and star-like objects which are attributed to the gel. At excess amounts of SDS, in the colorless solution, only small objects are detected. In the ovalbumin–DOTAC–water and BSA–DOTAC–water systems large aggregates are also observed in the bluish solutions. Colorless solutions for these two systems show the presence of small objects in the cryo-TEM micrographs. Ultrathin sections of the lysozyme and ovalbumin gels fixed with OsO4 also show the presence of aggregated structures as judged from the transmission electron microscopy observations.

Formation of Fatty Acid Salt-Induced Gel of Ovalbumin and the Mechanism for Gelation

Gelation of ovalbumin (OVA) was induced by the addition of fatty acid salts (FAS), such as sodium caprate (NaC10:0), to the protein solution at ambient temperature. The rheological and structural p...

Structure and dynamics of ovalbumin gels: II. Gels induced by heat treatment at 80°C

Abstract Dynamic viscoelastic measurements were made on ovalbumin gels prepared by two different thermal denaturation methods for a study of their gel structures. Results are discussed in the light of the fractal concept developed for the critical gel structure of synthetic polymers at the sol–gel transition point. Especially, a role of added salt on association kinetics of denatured proteins as well as on the resulting gel structures are described in detail.

Textural Properties of Pressure‐Induced Gels of Food Proteins Obtained under Different Temperatures including Subzero

ABSTRACTHigh‐pressure‐induced gelation of ovalbumin, egg yolk and soy protein was studied by pressurization up to 500 MPa for 30 min at ‐20 to 50°C; hardness, cohesiveness and gumminess of the gels were compared to those of gels obtained by heating at 100°C for 10 min. In the range ‐5 to 50°C, ovalbumin gelation showed a minimum at 25°C at all pressures applied. Operating at low temperatures allowed a reduction in pressure required to provide rather hard gels. With egg yolk and soy protein, gelation effectiveness progressively and continuously decreased with decreasing temperatures; the decrease was sharper with egg yolk.

Positron annihilation lifetime studies of free volume in ovalbumin gels

The dependence upon concentration of sodium chloride of free volume in ovalbumin gels, a main component of an egg white, is studied by the positron annihilation lifetime technique. The average free-volume radius in ovalbumin gels was about 0.27 nm at 298 K, smaller than those of organic polymers such as low-density polyethylene (0.34 nm at 300 K) and polystyrene (0.29 nm at 300 K). These differences suggest that the positronium annihilates in free volumes located close to hydrogen bonds, thus decreasing average free-volume radius. Free-volume content decreased with the increase of NaCl concentration up to 30 mM. At lower concentrations of NaCl, it seems that a correlation exists between microscopic free volume and macroscopic hardness of the ovalbumin.

Gelation Properties of Ovalbumin as Affected by Fatty Acid Salts

ABSTRACTThe physicochemical properties of heat‐induced ovalbumin (OVA) gels containing fatty acid salts (FAS) were investigated. Water‐holding ability and transparency markedly increased in the presence of sodium caprate or sodium laurate. At 9% of the protein concentration transparent and hard gels formed; at 7%, transparent and soft gels formed. Scanning electron microscopy showed that the transparent gels had a more homogeneous structure than turbid gels without FAS. Differential scanning calorimetry indicated that denaturation temperature of OVA was decreased and the peaks became broader after addition of FAS.

EFFECT OF pH AND CATIONS ON THE THERMALLY INDUCED GELATION OF OVALBUMIN

ABSTRACTThe gelation of ovalbumin in the presence of salts containing Ca+2 and Mg+2 at various pH values was investigated. Characteristics of the gels produced were evaluated using penetration measurements on an Ottawa Texture Measuring System as well as dynamic rheology on a Bohlin VOR rheometer. Gel properties were related to cation binding (equilibrium dialysis) and to changes in protein structure (differential scanning calorimetry). Cation binding generally increased with increasing salt concentration, and Mg+2 bound to a greater extent than Ca+2 at the higher levels studied. The impact of this binding on gel structure was dependent on pH and the technique used to evaluate structure. At pH 5 proteins tended to coagulate regardless of the type or amount of salt. At pH 7, the highest rigidity values from penetration measurements were obtained at salt levels of 0.005 M. At pH 9, the salt concentration for maximum rigidity varied with the salt, while the storage moduli (G') from dynamic rheology were highest at the highest salt concentration used. Based on rigidity data, the inclusion of 0.005 M MgSo4 would give a product with the greatest rigidity over a wide pH range.

Specific Disulfide Bond in α‐Lactalbumin Infiuences Heat‐ Induced Gelation of α‐Lactalbumin‐Ovalbumin‐Mixed Gels

ABSTRACTThe gel strength of ovalbumin mixed with α‐lactalbumin (α‐La) was determined after heating at 80°C for 15 min at pH 7.0 Gel strength of the mixture of 4%α‐La and 4% ovalbumin was two times that of 8% ovalbumin. Modified α‐La at Cys6‐Cys120 (3 SSα‐La) had low enhancement effects on ovalbumin gelation. Competitive ELISA using monoclonal antibody to α‐La showed decreased binding reactivities after heating α‐La with ovalbumin at specific concentrations. The decrease of total SH groups in the gel mixed with 3SS α‐La was much less than when mixed with α‐La. A disulfide bond of Cys6‐Cys120 in α‐La contributed to interactions between ovalbumin and α‐La in heat‐induced gels.

Structure and dynamics of ovalbumin gels: 1. Gel induced by high-temperature heat treatment

Dynamic viscoelastic (DVE) measurements are made on seven ovalbumin (OVA) gel samples induced by thermal denaturation of aqueous suspensions of OVA with OVA concentration C ranging from 12 to 45 wt% at 160°C for 5 min and subsequent moulding under pressure, and also on four OVA gels with higher C prepared by slow evaporation of water from the 45 wt% gel. The storage and loss shear moduli, G′( ω) and G″( ω), of OVA gels with C in the range of 30–59 wt% show angular frequency ω dependence characteristic of the critical gel with the fractal structure, i.e. G′( ω) ∼ G″( ω) ∼ ω″ and tan δ = tan(nπ/2) over the whole ω range of 0.14–100 rad s −1 measured at three temperatures of 5.0, 25.0 and 45.0°C. This finding is confirmed by shear creep and creep recovery measurements as well as dynamic light scattering measurements on the same gels. The critical gel structure, however, is not formed either for gels with C < 25 wt% or for gels with C > 59 wt%.

Characteristics of Ovalubumin Gel Layer Formed on Ceramic Microfiltration Membranes.

Ovalbumin solution, which is known to form a gel layer on membrane surfaces, was filtrated in a cross-flow mode using ceramic microfiltration membranes. The influences of pH and ionic strength of the ovalbumin solution on the properties of the gel layer and membrane permeability were studied.At a pH near the isoelectric point of the ovalbumin solution, both the permeate flux and ovalbumin rejection showed the lowest value. The cohesion force acting among ovalbumin molecules became strongest because the electrostatic repulsion force among the molecules was weakened, and then the gel layer was tightly adsorbed onto the membrane surface. Therefore, the membrane permeate flux obtained at the pH of the isoelectric point was smaller than that obtained at the other pH. The ovalbumin rejection increased at the other pH, except for the isoelectric point, because of the electrostatic repulsion of the ovalbumin gel layer formed on the membrane surface. The influence of electric charge was also recognized in the case of the filtration of sodium L-glutamate solution using the ovalbumin gel layer.When the ovalbumin solution was filtered with a high ionic strength, the permeate flux and the ovalbumin rejection were almost constant, independent of the solution pH.The molecular weight cut-off values of the ovalbumin gel layer were about 200,000–300,000 as self-rejecting dynamic membranes.The specific resistance of the ovalbumin gel layer obtained in dead-end filtration increased in pH near the isoelectric point and with increasing ionic strength of the feed solution. This tendency of the specific resistances was in good agreement with the behavior of the permeate flux of the ovalbumin solution.

Temperature dependence of the effective thermal conductivity of food gels impregnated with air bubbles.

Air-impregnated alginate and ovalbumin gels were prepared as model systems for porous foods, and their effective thermal conductivity was measured at 30–70°C by a steady-state method. The effective thermal conductivity of the air-impregnated gels increased with temperature more greatly than that of gels containing no air bubbles. For effective thermal conductivity of air-impregnated gels, a theoretical model which included latent heat transport accompanied by water vapor diffusion in addition to heat conduction was presented and was compared with experimental data. The model gave a good approximation to the experimental data up to 50°C. At higher temperature, however, the model overestimated the effective thermal conductivity, especially for gels of high porosity.

Elastic Attributes of Heated Egg Protein Gels

ABSTRACTThe equilibrium stress of egg white (EW) and ovalbumin (OV) gels using the statistical theory of rubber elasticity suggested that 3.9 covalent disulfide cross‐links per OV molecule were formed on gelling. DTNB and PCMB reacted with approximately 4 sulfhydryls of OV in 2% SDS and/or at 82°C. Moreover, the equivalent of 3 secondary bonds, calculated from the initial stress and presumably a composite of numerous weak secondary bonds, contributed significantly to the protein gel stress.

Modeling Gelation of Egg Albumen and Ovalbumin

ABSTRACTThe Flory gelation theory and a new protein gelation model were used to investigate the aggregation reactions of egg albumen and ovalbumin. Results showed that 178 to 267 ovalbumin monomers were required to establish the initial ovalbumin gel at the gel point temperature, 81°C. The gel point temperature for egg albumen was 72°C by the Instron and 60°C by protein solubility. The values of the activation energy rate constants for the formation of the different aggregates in the pre‐gel stage suggested that the larger ovalbumin aggregates were more reactive than the smaller ones.

Melting of heat-induced ovalbumin gel by pressure

The effects of pressure on heat-induced gels of ovalbumin were examined. A heat-induced gel containing 7% ovalbumin and 10 mmol/dm 3 Na-phosphate buffer, pH 7.0, melted completely with pressure at 600 MPa for 20 min at 20°C. The melted sample gelled again after the pressure ceased. Most of the heat-induced gels of ovalbumin prepared under various conditions (different protein concentrations, ionic strengths, pHs and heating methods) melted partly with pressure at 600 MPa for 20 min at 20°C, and gelled again at atmospheric pressure. However, a heat-induced gel of glycinin and cold-set gels of gelatin or agarose did not melt with pressure at 400–700 MPa for 20 min at 20°C. The pressure denaturation of ovalbumin and the renaturation of heat-denatured ovalbumin caused by pressure were also examined. The pressure denaturation of ovalbumin was partly reversible and heat-denatured ovalbumin renatured somewhat with treatment at 600 MPa for 20 min at pH 7.0 and low ionic strength.

Melting of the Ovalbumin Gels by Heating: Reversibility between Gel and Sol.

Heat-induced ovalbumin gels prepared under given conditions were melted with a second heating to below 90°C. The sample melted was gelled again on cooling. This gel-sol transition, which was detected both by eye and by the change in the dynamic viscoelastic parameters G' and G, was reversible. Differential scanning calorimetry showed that the endothermic heat flow that accompanied the gel-sol transition was much lower than that accompanied the denaturation of ovalbumin. With the repetition of the gel-sol transition, intermolecular disulfide bridges were formed, detected by sodium dodecyl sulfate-polyacrylamide electrophoresis done without a reducing agent.