Selected Rheological Properties of pH-Adjusted or Succinylated Egg Albumen

Apparent viscosities of pH-adjusted or succinylated raw egg albumen were measured at 10, 20, and 30°C using a Haake rotary viscometer. Viscosities decreased with increasing temperature. Rheological power law model parameters indicated that as pH approached 5–6 and 11, albumen became more Newtonian. Control albumen (pH 9.0) and succinylated albumen were pseudoplastic. Intrinsic viscosities of DH 9.0, 10.0, and 11.0 albumens were 0.083, 0.092, and 0.102 dl/g, respectively, and that of succinylated albumend (0, 0.1, 0.2, and 0.4% w/w) were 0.052, 0.147, 0.149, and 0.184 dl/g, respectively. Apparent viscosities of coagulated albumen, measured by capillary extrusion, increased with pH but did not change with succinylation. Yield forces and rigidity moduli of these gels increased with pH but not with succinylation level.     

Changes in Heat-Induced Rheological Properties During Cold Storage of Egg Albumen

Two groups of eggs were stored at 15°C for 0, 5 and 10 days. One group was stored, with the shell removed, in sterile Whirl-Pak bags. A second group was stored as intact whole eggs. Viscosity index, apparent elasticity, and initial penetration force were determined for heat-induced (80°C, 80 min) gels of the thick, thin and mixed albumens from each group. The rheological parameters increased with storage time, with the greater increase exhibited by the gels of the albumens that were stored as shell eggs. Solution pH was a major factor controlling these rheological properties of heated egg albumen.     

Heat-induced Egg White Gels as Affected by pH

The functional properties of heat-induced egg white gels were investigated at five pH values. Textural characteristics were determined using the Instron Universal Machine. Hardness, elasticity, cohesiveness, chewiness, and fracturability were maximum at pH 11. Hunter L values were maximum at pH 5 and 7. Microstructure studied with electron microscopy was distinctly different at the five pH values. Alkaline gels showed a fine ordered network that might have contributed to excellent textural characteristics. Water-holding capacity (WHC) was high at alkaline pH, but decreased with addition of 2-mercaptoethanol, suggesting that disulfide bonds were important in egg white gels. Sodium dodecyl sulfate (SDS) improved WHC at pH 7 and 9. No significant correlation was observed between textural profiles and WHC.     

Mechanical and Barrier Properties of Egg Albumen Films

Films were cast and dried from heated, alkaline aqueous egg albumen solutions containing glycerin (GLY) at 30, 40, or 50% w/w of protein, polyethylene glycol (PEG) at 50 or 60%, or sorbitol (S) at 50 or 60% as plasticizers. PEG-plasticized (60%) films also were prepared by substituting 10, 30, 50, or 70% of albumen with yolk solids. Film tensile strength (TS), elongation at break (E), water vapor permeability (WVP), and Hunter color values were measured. At a plasticizer content of 50%, films with S had the lowest WVP while films with PEG had the greatest E. S- and PEG-plasticized films had greater TS than GLY-plasticized films. Yolk solids decreased film TS, E, and WVP while increasing film yellowness.     

转谷氨酰胺酶提高蛋清粉凝胶性能的研究

为改善蛋清粉的加工品质,探讨了酶交联反应对提高蛋清粉凝胶性能的影响。通过研究转谷氨酰胺酶用量、反应温度及作用时间对蛋清粉凝胶强度的影响,采用Box-Benhnken设计对转谷氨酰胺酶交联蛋清粉的凝胶强度进行优化。以蛋清粉凝胶强度为响应值,进行响应面分析。结果表明,转谷氨酰胺酶交联蛋清粉的优化工艺条件为:酶用量6U/g蛋清粉,作用时间3.99h,温度35℃,在此条件下,蛋白粉的凝胶强度达到820g/cm2,与实测值基本一致,说明利用该试验建立的模型在实践中具有可行性。     

Rheological Properties of Concentrated Wheat Starch Gels

The rheological properties of concentrated wheat starch gels were measured with shear stress relaxation experiments in cone-plate geometry. The water content of the investigated gels were 80, 60, 50 and 30% (w/w), respectively, and the relaxation modulus (G) and half relaxation time (T1/2) were studied after heating to different temperatures. For the gels with 50% and 60% (w/w) of water, a maximum value of G was obtained when the temperature interval for gelatinization was passed. When these gels were heated to higher temperatures, G decreased, and T1/2 increased, whereas gels with 30 and 80% (w/w) of water behaved differently. The influence of particle size distribution on the rheological properties of concentrated starch gels, was also investigated. It was found that G and T1/2 increased with a greater fraction of small starch granules.     

Rheological Properties of Two Heat-Induced Protein Gels

Rheological properties of heat-induced gels from egg albumen and bovine plasma proteins were measured using a mechanical loading device. Each protein was tested at 8% protein concentration and heated for 0–120 min at 80°C in an agitating water bath. After heating, the viscosity index, apparent elasticity and initial penetration force of the gels were evaluated. Bovine plasma protein dispersions exhibited a substantially higher viscosity index, apparent elasticity and initial penetration force than egg albumen gels. Bovine plasma proteins produced a gel structure which was strong and elastic. By comparison, heat-induced gels of egg albumen proteins were fragile and somewhat brittle.     

Correlation of the Rheological Behavior of Egg Albumen to Temperature, pH, and NaCl Concentration

Rheological parameters of viscosity, gel strength, and elasticity were determined on heat-set egg albumen gels over various treatment combinations ranging from 65-90°C, pH 6.4-9.6, and NaCl concentrations of 0.0-0.1M added NaCl. Maximum viscosity was measured at a treatment combination of 77.5°C, pH 8.00, and 0.1M NaCl. Elasticity and gel strength were highest in gels with a treatment combination of 85.2°C, pH 9.0, and 0.08M NaCl. Temperature had the greatest effect on all three rheological parameters. Gels heated above 80°C were of unusual character, exhibiting syneresis and shrinkage.     

不同大豆分离蛋白凝胶的流变学性质

本文比较研究了三种不同大豆分离蛋白(分别为SG、ADM和ON)的凝胶性能。三种大豆分离蛋白的7S／11S比率和变性热焓类似，但表面疏水性和混浊度却明显不同。通过小变形振荡流变分析研究了三种大豆分离蛋白的热凝胶性能。在去离子水中，SG和ADM的凝胶浓度均是90mg／ml，且两者的凝胶强度接近；ON的凝胶浓度是110mg／ml。在1．0mol／L NaCl溶液中，ADM的凝胶强度高于SG。在NaSCN存在的情况下。ON的凝胶强度明显增加。尽管N-乙基马来酰亚胺(NEM)能够封闭巯基，但该试剂可增强三种大豆分离蛋白的凝胶强度。结果显示SG和ADM之间的凝胶性能的差别主要是由于表面疏水性不同，而造成ON凝胶性能较差的主要原因是大豆蛋白分子的聚集。     

Preparation of Heat-induced Transparent Gels from Egg White by the Control of pH and Ionic Strength of the Medium

Egg white was dialyzed against distilled water or diluted with water, and the precipitates formed were removed by centrifugation. The supernatant gave a transparent gel after being heated at an acidic pH (2–4). At other regions of pH, except for the highly alkaline region, the gel or suspension was turbid upon heating. Insufficient centrifugation of the dialyzed egg white or the addition of NaCl to the supernatant after centrifugation resulted in a turbid gel on heating at even acidic pH. The removal of the slight precipitate formed at low ionic strength and the maintenance of low ionic strength during heating were both necessary for production of a transparent gel.     

Foaming Properties of Egg Albumen with a Bubbling Apparatus Compared with Whipping

Neither standard method nor instrument exists to accurately measure foaming properties in food. Usually, whipping methods are used but they are only moderately reproducible. We used an original apparatus in which foam was generated by bubbling and then analyzed by conductimetry (liquid in the foam) and a uniline camera (foam volume). The foaming properties of a series of egg-white powders were studied. Among parameters describing foam formation and destabilization, three were repeatable and discriminating. They were correlated with those obtained with whipping methods. Easy to use and rapid, the bubbling method is an alternative for controlling and measuring the foaming properties of egg-white.     

Simultaneous Isolation of Avidin and Lysozyme from Egg Albumen

A single column cation exchange method was developed which allowed simultaneous recovery of lysozyme and avidin from undiluted egg white. A unique application-elution sequence was developed, involving accumulation of avidin on the column through several cycles of egg white application and lysozyme elution. Lysozyme was recovered with higher yields than reported for the isoelectric precipitation methods often used in the industry (86% vs 60–80%). Lysozyme peaks appeared homogeneous on SDS-PAGE. Avidin recovery was also as good or better than that of previously reported ion exchange methods (74%–80%). The purity of the avidin fraction (up to 40.9%) was superior to that of other reported primary avidin fractions.     

Factors Contributing to Antilisterial Effects of Raw Egg Albumen

Sensitivity of Listeria monocytogenes strain Scott A and Brie-1 to several factors in raw egg albumen was investigated. A concentration of ca 15% of albumen in trypticase soy broth was listeristatic after 24 hr at 35°C, and listericidal effects were observed at higher concentrations. Supplementation of albumen with iron or biotin did not reverse the inhibition. Preheating of albumen (50–80°C) caused progressive loss of antilisterial effects. Supplementation of broth with lysozyme (>1 mg/mL) produced antilisterial effects that were enhanced at pH 9; conalbumin (>6 mg/mL) suppressed cell growth, while ovomucoid (>2 mg/mL) was inhibitory only at pH 9. Results inferred that antilisterial effects of albumen were caused primarily by lysozyme and were enhanced by ovomucoid, conalbumin, and alkaline pH.     

Rheological Properties of Liquid Egg Products (LEPS)

Rheological properties were determined at 4°C (refrigerated temperature), 25°C (room temperature), 60°C (pasteurization temperature) for liquid whole egg (LWE) and liquid egg yolk (LEY) and 4, 25, 55.6°C for liquid egg white (LEW) by using concentric cylinder viscometer. The shear rate range was 8 to 53.7 s^?1 for LEW and LWE, and 1 to 34 s^?1 for LEY. Selected physical properties (e.g., density) of LEPs were studied at broad range of temperatures from 4°C to 60°C. All liquid egg products (LEPs) exhibited mildly shear thinning (pseudoplastic) behavior. Experimental data of LWE and LEW successfully fitted Herschel-Bulkley model, LEY data were well described by power law model. LEW and LWE showed thixotropy and time-dependency at their pasteurization temperatures (55.6°C for LEW, 60°C for LWE) and considered being time-independent below these temperatures. LEY exhibited time-dependent behavior at 4°C and 60°C. But its rheological behavior showed no thixotropy and time-dependency at room temperature. The density of all three products decreased with increasing temperature. Density data were correlated by polynomial models (r² > 0.99).     

Comparison of Transparent Gels with Turbid Gels Prepared from Egg White: Creep Analysis of Gels

Egg white from which the precipitate occurring during dialysis against water had been removed gave a transparent gel on heating at lower salt concentrations and pH 3.54. The addition of NaCl or a shift of pH from 3.54 to 4.50 brought about the turbid gels. Creep analyses of these transparent and turbid gels were done using a four-element mechanical model. The instantaneous elastic modulus, E₀, Newtonian modulus, ηn and retarded viscoelastic moduli, E₁ and η₁ increased with NaCl up to 125 mM and then decreased with increase in NaCl concentration at pH 3.54. At 125 mM NaCl and pH 3.54, a translucent gel was obtained. E₀ and η₁ decreased with the temperature of the gel, while E₁ and η₁did not change depending of temperature.     

Rheological, Thermal and Microstructural Properties of Whey Protein-Cassava Starch Gels

Mixed gels of cassava starch (CS) and a whey protein isolate (WPI), obtained by heating solutions of 10% total solids, pH 5.75 to 85°C, were characterized as a function of the starch fraction, θ_s, by axial compression, small-amplitude oscillatory rheometry, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Gelation did not occur for θ_s > 0.7. In the range 0<θ_s < 0.4 mixed gels showed higher mechanical (E, elastic modulus) and rheological (G′, storage modulus) properties than pure gels, with maximum values for θ_s= 0.2–0.3. Viscoelastic measurements as a function of time showed that gels containing higher levels of WPI developed a larger G. Blends of both biopolymers showed independent thermal transitions in DSC measurements, related to gelatinization and denaturation. Microstructure of a mixed gel formed at θ_s= 0.2 showed a continuous matrix formed by strands of WPI particle aggregates and an independent CS phase.     

Modeling Gelation of Egg Albumen and Ovalbumin

The 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.     

Ultrastructural Examination of Egg Albumen Protein Foams

Transmission electron microscopy studies of protein foams revealed the presence of a layer of cross-linked polypeptides at the surface of the film enveloping an air inclusion. Scanning electron microscopic examination of a whipped solution with high levels of ovomucin and without lysozyme showed that the protein concentrated at the film surface and considerably decreased film continuity. The membrane appeared less cohesive in nature and draped fluidly over the torn edges. Inclusion of lysozyme improved the overall foam appearance. The effects of lysozyme on foaminess in the presence of ovomucin were apparently associated with formation of ovomucin-lysozyme complex. This complex seemed to alter the viscous nature of ovomucin.     

Effect of Chemical Modifications on Some Physicochemical Properties and Heat Coagulation of Egg Albumen

Egg albumen was modified with succinic anhydride and a water-soluble carbodiimide, 1-ethyl-3(3-dimethylaminopropyl) carbodiimide. The chemically modified proteins exhibited only minor conformational changes, but were altered in their responses to heat treatment. Heat-induced coagulation was retarded by both modifications suggesting that thermocoagulation requires a balanced electrostatic attraction between protein molecules. Hydrophobicity measurements and pH-titration data suggest the involvement of hydrophobic and ionic interactions in heat aggregation and gelation of egg white proteins. The soluble fraction of the heat-coagulated proteins contained mainly monomers, while under conditions where a gel or coagulum was not formed, the heat-treated egg albumen solutions contained high M.W. soluble aggregates. A scheme for the thermal coagulation of egg albumen is proposed.     

Heat-induced Gels of Rice Globulin: Comparison of Gel Properties with Soybean and Sesame Globulins

The hardness and water-holding ability of rice globulin gels were intermediate between those of gels of soybean and sesame globulins. Scanning electron micrographs showed that rice globulin gel had a rough network structure composed of small globular particles of protein aggregates. Effects of various reagents on solubilization of proteins from the three gel types were compared. Disulfide bonds and hydrophobic interactions contributed mainly to the stability of rice globulin gels. The contributions of disulfide bonds to both the formation and stability of rice globulin gels were greater than for sesame globulin gels.