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.     

Modification of Egg White Proteins with Oleic Acid

Studies on the chemical modification of egg white with oleic acid (5-50 moles/50,000g of egg white protein) revealed that the reagent partitioned equally between supernatant and precipitate. The mole ratio of oleic acid to protein in solution at the 20 mole level of treatment was 14.6:1. Oleic acid did not selectively precipitate ovalbumin, conalbumin, or lysozyme. An increase in negative charge of proteins was observed in the chromatograms of treated egg white. No difference in molecular weights of treated egg white proteins was observed. The viscosity varied with the concentration of the reagent. In cooked, frozen, and thawed egg white water retaining index was 1.5-10X greater for treated than untreated material.     

Separation of Native and Acylated Egg White Proteins with Gel Chromatography and DEAE-Cellulose Ion Exchange

Chemical modification of egg white has been shown to improve its functional properties. In order to fully understand the changes in functionality it is necessary to separate the proteins and study their corresponding structural changes. This paper describes two chromatographic techniques applied to the separation of native and acylated egg white. A molified DEAE—cellulose ion exchange methodology was developed which reduced separation time and expense. It was found that increases in net charge introduced by acylation with succinic or acetic anhydride changed the ionic state of the proteins, limiting their separation by ion-exchange chromatography. Using Sephacryl S-200, a gel chiomatographic technique was developed which separated over 80% of the total succinylated egg white proteins; viz., ovomucin, ovalbumin, conalbumin, ovomacroglobulin, and lysozyme. Most proteins of native and acetylated egg white were separated with S-200 chromatography, but required rechromatography of the ovalbumin-conalbumin fractions for complete resolution.     

A differential scanning calorimetric study of the stability of egg white to heat denaturation.

The heat denaturation of egg white and its component proteins was studied by differential scanning calorimetry. At a heating rate of 10 °C/min, egg white at pH 7 shows two major endotherms, at 65 °C and 84 °C, produced by the denaturation of conalbumin and ovalbumin, respectively. The conalbumin endotherm is increased to 70 °C by raising the pH to 9.0, or 77 °C by addition of aluminium at neutral pH. Addition of sucrose stabilises all the proteins; at 10%sucrose, all endotherms are shifted 2 °C to higher temperatures. Within experimental error, the enthalpy of denaturation of egg white equals the sum of the enthalpies of denaturation of its component proteins, and is independent of pH over the pH range 7–9.     

Preparation of Transparent Egg White Gel with Salt by Two-step Heating Method

A heat-induced transparent gel from egg white was prepared at low pH and low ionic strength by a one-step heating method. The addition of NaCl to the egg white formed a turbid gel on heating. Egg white, first diluted with water, gave a transparent solution upon heating of this mixture. The solution formed a transparent gel when heated with NaCl up to a concentration of 0.3M for a second time. The transparent gel obtained at 150 mM NaCl was more firm and less adhesive than the turbid gel prepared by the one-step heating method at the same pH, protein concentration, and NaCl concentration.     

Separation and identification of hen egg protein isoforms using SDS–PAGE and 2D gel electrophoresis with MALDI-TOF mass spectrometry

Knowledge of the chemical composition and physicochemical properties of native egg white and yolk is necessary to interpret the functional and biological properties attributed to specific egg components. To date, many of the proteins located in this complex biological fluid remain uncharacterised, if not unknown. High-resolution techniques for proteome analysis, including SDS–PAGE and 2-dimensional (2D) gel electrophoresis, combined with mass spectrometry, were employed to separate and identify several protein components in hen’s egg. An advanced and sensitive glycoprotein staining kit was used to detect the presence of glycosylated proteins in the egg samples. Numerous spots were revealed when a mixture of egg white and yolk was subjected to 2D gel electrophoresis. Several of the already known egg proteins were identified. Isoforms of ovalbumin and conalbumin were visualised. The presence of FLJ 10305 and Fatso proteins in the proteome of Gallus domesticus was also confirmed.     

Heat-Induced Aggregation of Egg White Proteins as Studied by Vertical Flat-Sheet Polyacrylamide Gel Electrophoresis

Heat-induced aggregation of proteins in egg white was investigated by a vertical flat-sheet polyacrylamide gel electrophoretic method. The fractional and step-wise aggregation of egg white proteins was caused by heating. Even with a heating time of 120 min, ovalbumin and globulins Al and A2 failed to aggregate in egg white (pH 7 and 9) at 70°C, and ovotransferrin and ovomucoid also did not aggregate in egg white at 60°C (pH 9) and 76°C (pH 7 and 9), respectively. The ovoinhibitor was much more unstable than ovomucoid under heat-treatment, and the time dependency of heat-induced aggregation of flavoprotein was greater than those of the other proteins in egg white.     

鸡蛋产品鉴伪技术的构建

本实验建立了一种综合蛋白质和基因组两种检测方法的鸡蛋产品鉴伪技术。一方面,研究选择鸡蛋蛋清中的溶菌酶、卵白蛋白、伴白蛋白作为蛋清蛋白质的标志性成分,采用改进后的离子交换树脂法对上述三种目标蛋白进行分离,经聚丙烯酰胺凝胶电泳分析从而实现蛋白质水平的鉴定。另一方面,针对鸡蛋产品中常见的掺假物玉米粉、大豆粉,以高等植物18S r DNA基因作为内源参照基因,设计这两种掺假物的特异引物进行PCR扩增,经过琼脂糖凝胶电泳显示特异性条带的有无,从基因组水平实现鸡蛋产品的鉴伪。结果表明:离子交换法对轻加工鸡蛋产品中有良好的鉴定效果,对深加工鸡蛋产品中蛋白质的提取效果欠佳;PCR反应设计的引物特异性良好,鸡蛋产品中掺杂的最低检测限可高达2%。结合离子交换树脂和PCR法两种检测手段可对市售大部分鸡蛋产品进行鉴定。      

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.     

Strength of Protein Gels Prepared with Microbial Transglutaminase as Related to Reaction Conditions

Influence of gelling reaction conditions on the strength of several protein gels prepared with microbial transglutaminase (TGase) was investigated. A method was developed to gel proteins and measure gel breaking strength in a micro well plate. Enzyme concentration range for maximum gel breaking strength varied from 10 to 40 units/g protein. Maxima gel breaking strengths were achieved at 50°C for SPI, caseinate and gelatin and 65°C for egg yolk and egg white proteins. Optimum pH resulting in strong gels was pH 9 for SPI, caseinate, and egg yolk, and pH 6 for gelatin and egg white. Adjusting pH was promoted in egg white the formation of ?-(γ-glutamyl)lysine crosslinks and increased its gel breaking strength.     

Heat-Induced Aggregation and Denaturation of Egg White Proteins in Acid Media

Heat-induced aggregation and denaturation of egg white proteins adjusted to pH 5.5, 4.5, 3.5 and 2.5 were investigated by vertical flat-sheet polyacrylamide gel electrophoretic and differential scanning calorimetric methods. The fractional and step-wise aggregation of egg white proteins was caused by heating. As the acidity was increased from pH 5.5 to 2.5, ovotransferrin, ovomacroglobulin, globulin G3A, globulins A1 and A2, and ovalbumin became much more unstable to heat. However, ovomucoid and ovoinhibitor did not aggregate in the acidified egg white under heat treatments of 3 min at 90°C or 20 min at 74°C. The heat-induced aggregation of flavoprotein was slightly greater at pH 4.5 and 3.5 than at pH 5.5 and 2.5.     

不同碱液对鸡蛋清凝胶特性的影响研究

以鸡蛋清为材料,探讨了NaOH、KOH和Na2CO3直接添加对蛋清凝胶强度、破裂强度、白度、透明度以及持水性的影响。结果表明:随着碱浓度的升高,蛋清的pH逐步提高,凝胶强度逐步降低;当碱浓度为0.1mol/L时,NaOH、KOH、Na2CO3的添加使蛋清凝胶强度由最初的156.2g分别下降至49.1、56.8、89.1g。蛋清凝胶的破裂强度随着碱浓度的增加呈现先上升后下降的趋势。3种碱液的加入,使得蛋清凝胶白度逐步下降,透明度先上升后下降,持水性逐渐升高。当NaOH和KOH在浓度≤0.04mol/L,Na2CO3在浓度≤0.1mol/L时,蛋清凝胶的pH<11,符合皮蛋腌制过程的pH范围;凝胶强度在70g以上;破裂强度较对照增大,凝胶不易破裂。      

The effect of storage on the proteins of frozen liquid egg and spray-dried egg

Storage of spray-dried whole egg and egg-milk mixture for about a year at 3–5°C resulted, in both cases, in a marked reduction in the proportion of insoluble proteins and an equally marked increase in the inert lipoprotein fraction of the soluble proteins; this fraction was clearly derived from the low density fraction of the yolk. Storage of frozen liquid egg for about a year in the frozen state resulted in the insoluble protein fraction of the thawed egg having more water bound in it than did the corresponding fraction of the freshly-frozen egg, but in neither case did the insoluble proteins have as much water bound with them as those of the reconstituted spray-dried samples. Spray-drying results in only a partial reduction in the contents of ovalbumin, ovomucoid and conalbumin, and addition of milk to the whole egg before spray-drying improves the stability of these proteins. They appear to be little changed by freezing and storing in the frozen state. There is evidence that ovalbumin is present in a more stable form in processed egg products than in new-laid raw egg.     

Impact of pH on the interactions between whey and egg white proteins as assessed by the foamability of their mixtures

The impact of protein–protein interactions on foaming properties of mixtures consisting of egg white proteins (EWP) and whey proteins (WP) with total protein content of 60 g/L was examined at pH 5, 7 and 9. The ratio between EWP and WP in the mixtures was varied between 67:33, 50:50 and 33:67 (in %; w/w). The ionic strength was adjusted to that of milk (I = 176 mM). The foamability of the protein products was characterized by the foam capacity, stability and firmness. In addition, the hydrophobicity in the protein solutions was assessed as a measure for the physical behaviour and ability of proteins to adsorb at the air–water interface.The individual egg white proteins and whey proteins each showed the best foaming properties at pH 5 and pH 9, respectively. At pH 9 a synergism was observed in the capacity and stability of the foams from EWP/WP-mixtures. This effect appears to be caused by the electrostatic interactions between egg white and whey proteins which occur in the bulk solution after the pH adjustment prior to the foaming. In contrast, at pH 5 no positive influence of foaming the components in a mixture as well as no indication of intermolecular interactions was found. At pH value near the pI of ovalbumin the protein interactions occur when the proteins have adsorbed at the air–water interface. The protein systems foamed at pH 7 showed intermediate foamability compared to the values obtained at alkaline and acidic pH.     

Influence of pH and Salts on Egg White Gelation

ABSTRACT: Egg white is used in food products for various functional properties. These are strongly influenced by pH, ionic strength, type and concentration of salts. Through an experimental design strategy, the aim of this study was to quantify the influence of pH, cations, and anions naturally present in egg white, and of citrate on egg white gelation. Results showed that pH and Fe³⁺ modified the coagulation temperature of egg white and consequently, the gel characteristics. High concentrations of NaCl decreased the water-holding capacity and the microstructure of egg white gels. At pH 7, viscoelastic properties and microstructure of egg white gels were altered by Ca²⁺ and Mg²⁺ addition.     

Selenium distribution in egg white proteins

The present studies were undertaken to characterize selenium distribution in egg white. Ion-exchange chromatography fast protein liquid chromatography (FPLC) and flow injection atomic (absorption) spectrometry (FIAS) were used to separate egg white proteins and to determine the selenium content of different fractions. After purification, nine different proteins were identified with sodium dodecyl sulphate-polyacrylamide gel electrophoresis and 56% of the total selenium content was found to be associated with ovalbumin –1 and –2 (±500 ng/g), which is the main protein in egg white. Flavoprotein was determined to be the richest seleniumcontaining protein (1800 ng/g). The selenium content of the other proteins (lysozyme, conalbumin, globulins and ovomucoid) ranged from 359 to 1094 ng/g.

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Selen-Verteilung in Eier-Eiweißproteinen

Zusammenfassung Die vorliegenden Studien wurden vorgenommen, um die Selen-Verteilung in Eiweiß zu charakterisieren. Ionenaustauschchromatographie und Atomabsorptionspektrometrie wurden gebraucht, um Eiweißproteine zu trennen und den Selengehalt verschiedener Fraktionen zu bestimmen. Nach Isolation wurden neun verschiedene Proteine mit SDS-PAGE identifiziert und 56% des totalen Seleninhalts ist an Ovalbumin-1 und –2 (zirka 500 ng/g) gebunden, was dem höchsten Proteinwert in Eiweiß entspricht. Flavoprotein war das an Selen reichhaltigste Protein (1800 ng/g). Der Seleninhalt der anderen Proteine Lysozym, Conalbumin, Glo bulin und Ovomucoid lag zwischen 359 und 1094 ng/g.

     

超声波加工对蛋清蛋白质结构和凝胶特性的影响

为研究超声波加工对蛋清蛋白质结构和凝胶特性的影响,以蛋清为原料进行超声处理,通过对超声前后蛋清蛋白质的空间结构、分子分布和流变学性能进行分析,同时对超声后蛋清凝胶的保水性、质构特性等进行测定。结果表明,在200 W和400 W的超声处理下,蛋清蛋白发生了折叠和聚集,也有小部分发生了降解。在600 W的超声处理下,蛋清蛋白发生了部分降解,同时还有小部分蛋白发生了聚集。因此,超声使部分蛋白质分子粒径变大,部分蛋白质分子粒径变小,整体分子粒径分布变窄。200 W、10 min 和600 W、30 min 的超声处理下,蛋清溶液偏向于液体的流变性。在200、400 W和600 W 3 种功率的超声处理下,蛋清凝胶的保水性增强。200 W和400 W的超声处理有利于增强蛋清的凝胶强度,使凝胶更加坚固和致密。600 W、30 min的超声处理会使蛋清的凝胶强度显著降低,从而使凝胶的稳定性降低。研究结果可为改善蛋清的凝胶性能提供一定的参考。     

Comparative study of egg white proteins from different species by chromatographic and electrophoretic methods

This work describes the use of different high-resolution techniques to study egg white proteins from hen, quail, duck, pheasant and ostrich. For this purpose, reversed-phase high-performance liquid chromatography, sodium dodecyl sulfate–polyacrylamide gel electrophoresis and isoelectric focusing (IEF) were used to compare egg white proteins from these poultry species. The major proteins, lysozyme, ovalbumin, ovomucoid and ovotransferrin, were separated and identified using the three techniques. Isoforms of ovotransferrin and ovalbumin in some species were observed when IEF with gels of pH 4–6 were used. Qualitative and quantitative differences were observed among the individual proteins of the different species investigated.     

Electrophoresis and Chromatography of Heat-Treated Plain, Sugared and Salted Whole Egg

The effects of heat treatments on the proteins in plain, 10% sugared and 10% salted whole egg were studied by polyacrylamide disc gel electrophoresis and diethylaminoethyl-Sephacel ion exchange chromatography. Electrophoretograms of products heated from 57–87°C for 3.5 min showed a wide range of protein stability. Livetins and some globulins were most heat sensitive, while conalbumin and ovalbumin were most stable. Sugar and salt increased heat stability of proteins by 1.6 and 7.9°C, respectively. Heat sensitive proteins were most stabilized by sugar and salt. Heating whole egg and sugared whole egg changed the chromatograms substantially, while heating salted whole egg caused fewer changes.     

Rheological Properties of Heat-Induced Ovalbumin Gels Prepared by Two-step and One-step Heating Methods

Ovalbumin gave a transparent solution, transparent gel, or opaque gel on heating at low ionic strength, but a turbid gel, or turbid suspension at high ionic strength (one-step heating). The ovalbumin solution, once heated at low ionic strength, gave a transparent gel with a second heating at high ionic strength (two-step heating). Textural parameters of hardness and adhesiveness, viscoelastic parameters from creep curves, breaking energy and water-holding capacity of these gels were measured. Transparent gels by the one- or two-step heating were firm and elastic and had high water-holding capacity. Turbid gels by one-step heating were soft and less elastic and had low water-holding capacity. The relationship between gel properties and structure was discussed.