Stability and Rheological Properties of Egg Yolk Granule Stabilized Emulsions with Pectin and Guar Gum

The effects of pectin and guar gum on rheology, microstructure and creaming stability of 1% (w/v) egg yolk granule stabilized emulsions were investigated. While the addition of low amount of pectin (0.1% (w/v)) had no effect on the emulsion viscosity, the addition of 0.5% (w/v) pectin greatly increased the viscosity. Granule-stabilized emulsion without hydrocolloids reflects the pseudoplastic behavior (shear-thinning behavior with flow behavior index, n < 1.0). Hydrocolloids, especially at high concentrations, affected the viscoelastic behavior of the emulsions and both storage (G′) and loss modulus (G′′) were regarded as frequency dependent. Emulsions behaved like a liquid with G′′ > G′ at lower frequencies, and like an elastic solid with G′ > G′′ at higher frequencies. Emulsion microstructure indicated that the presence of hydrocolloids induced flocculation. Creaming stability of emulsions was enhanced by the presence of hydrocolloids and increasing hydrocolloid concentration decreased the creaming by restricting the movement of oil droplets.     

Cholesterol Content and Functionality of Plasma and Granules Fractionated from Egg Yolk

In low-salt aqueous solution, nonspray-dried (NS) and spray-dried (SD) egg yolk were fractionated into granule and plasma fractions using ccntrifugation. The following determinations were made on each fraction: total cholesterol, lipid, protein, emulsifying activity (EA) and stability, foam capacity and stability, and protein solubility index. Fractionation of NS to granules resulted in -30% reduction (p ≤ 0.01) in cholesterol, a 46% reduction in lipid, and a twofold increase in protein. In decreasing order (p ≤ 0.01), EA of NS products in distilled water was: plasma > NS > granules. Emulsion and foam stability values exhibited by granules of NS suggest they could be used as a stabilizer of dispersion system.     

Effect of hydrocolloids on the thermal denaturation of proteins

The thermal denaturation of bovine serum albumin (BSA), lysozyme and whey protein isolate (WPI) in the presence of hydrocolloids (pectin, guar gum, ι-carrageenan) was investigated. A decrease in the thermal stability of lysozyme was observed in the mixture of protein with ι-carrageenan. The increase in the enthalpy of denaturation (ΔH) of BSA and lysozyme in the presence of hydrocolloids was attributed to the protection of globular proteins against aggregation through blockage of their hydrophobic binding sites by the bulky polysaccharide moeity. Biopolymers had a stabilizing effect on WPI. The thermal stability was the highest in the presence of pectin, whereas the lowest transition temperature was observed in the presence of guar gum. A single transition peak was observed for pure WPI. However, WPI exhibited two transition temperatures when together with pectin and i-carrageenan. WPI was stable against heat denaturation at acidic pH values (pH 4.0), while it was denatured at a low temperature at an alkaline pH (pH 9.0) in the presence of pectin. This was attributed to the formation of extra hydrogen bonding. The increase in the concentration of pectin has little affect on the heat stability of WPI; however, it reduces the cooperativity of transition.     

Effects of sucrose and sodium chloride on foaming properties of egg white proteins

Egg white proteins are extensively utilised in the food industry as foaming agents. A number of factors, singly or in combination, can affect the foaming characteristics of egg albumen. In this study, egg white protein solutions heated at various temperatures in the presence of variable concentrations of sucrose and NaCl were whipped for different periods of time. All factors had a significant impact on the foaming properties of egg albumen. Increasing NaCl content and whipping time enhanced protein adsorption at the air–water interface. The presence of sucrose delayed foam formation but contributed to the stability of the aerated system. Controlled denaturation of the protein solutions induced by mild heat treatment enhanced the foaming properties of egg white proteins. This data indicates that the foaming properties of egg white proteins can be manipulated by altering the effect of extrinsic factors in order to achieve optimal formulations for food industrial applications.     

Impact of a thermal treatment on the emulsifying properties of egg yolk. Part 1: Effect of the heating time

The denaturation degree of egg yolk (EY) protein was determined in dilute EY suspensions containing 20% fresh EY (w/w) as a function of the heating time (0–40 min.) at 74 °C. The impact of such a thermal treatment on the emulsifying properties of the EY was studied in a fluid oil-in-water (O/W) emulsion containing 30% oil (v/v). Heating of the EY prior to emulsification appeared to slightly increase the oil droplet size and to drastically decrease of the level of flocculation. It was also shown that the concentration of proteins in the interfacial film increases with increasing degree of EY protein denaturation, which is thought to be responsible for the change in the colloidal interactions between droplets. The increased steric repulsions due to the increased interfacial protein concentration could explain the decrease of oil droplet flocculation. The impact of such modifications on the rheological properties and creaming stability of the emulsions is discussed.     

Egg yolk protein modification by controlled enzymatic hydrolysis for improved functionalities

Delipidated egg yolk protein (EYP) is produced as a co-product of egg yolk lecithin extraction. This EYP is expected to have poor functionality because of protein denaturation caused by ethanol treatment during lecithin extraction. Two food grade endo-proteases were used to produce EYP hydrolysates (EYPh) with two degrees of hydrolysis (DH), 3% and 6%. Protein solubility was improved as DH increased. Solubility profiles for both EYP and EYPh were relatively less pH-dependent compared with soy protein. Except for foaming capacity, EYPh showed improvement in foam stability, foaming speed, and foam density. Emulsion stability was improved for all EYPhs. Treatments at DH of 6% showed significant increase in emulsification capacity. We have shown quantitatively how controlled enzymatic hydrolysis can be applied to ethanol-treated lipid-free EYP to increase protein solubility, and thus to improve foaming and emulsification properties.     

Modification of functional properties of egg‐white proteins

Egg‐white proteins are extensively utilised as food ingredients due to their unique functional properties. Several attempts have been made in order to improve the functional properties of egg‐white proteins and to identify the optimal formulations for unique food products. Experimental data proves that controlled denaturation of egg‐white proteins can have a beneficial impact on various functional applications in the food industry such as emulsifying ability, heat stability, gelation. This review describes the effect of heat‐induced denaturation on protein structure and functionality. Studies on the impact of Maillard reaction, which aim to elucidate the structure‐function relationship of egg‐white proteins, are presented. A novel approach which could be the basis for the development of new methods aiming to improve the functional properties of egg‐white proteins is also discussed.     

热处理对酶改性蛋黄液乳化性的影响及拉曼光谱分析

蛋黄液对热敏感,64 ℃左右开始变性形成凝胶,加工过程中的热处理会导致其乳化性质下降,限制了其在食品工业中的应用。因此,本实验研究不同热处理条件（60、65、70 ℃均处理4 min）对酶改性蛋黄液乳化性质及蛋白质结构的影响。结果表明：随着热处理温度的升高,蛋黄液的乳化活性呈现下降的趋势,所形成的乳化体系平均粒径表现出增大的趋势。同一热处理条件下,酶改性蛋黄液的乳化活性及乳化稳定性均显著高于未改性蛋黄液（P＜0.05）,酶改性蛋黄液所形成的乳化体系粒径明显减小,粒径分布更加接近正态分布。拉曼光谱分析结果显示,在不同热处理条件下酶改性蛋黄液中蛋白质二级结构发生变化,在65 ℃以下随温度升高α-螺旋结构相对含量显著升高,无规卷曲结构相对含量显著下降（P＜0.05）;其色氨酸残基、酪氨酸残基及脂肪族疏水基团较未改性蛋黄液更倾向于暴露。采用偏最小二乘法建立了基于拉曼光谱的蛋黄液乳化性质模型,结果表明蛋黄液中蛋白质二级结构及构象变化（特别是低密度脂蛋白的构象变化）对蛋黄液乳化性质影响最大。     

Functional Properties of Milk-Egg Mixtures

We used an experimental design (Scheffe simplex-centroid design) to examine ingredient interactions in food protein mixtures and their effects on functional properties. A defined and limited number of milk, albumen, and egg yolk blends were made and evaluated for heat gelation properties and for emulsifying and foaming capacity and stability. The method accounted for nonlinear interactions between the ingredients. Synergistic effects were revealed on heat gelation and emulsifying properties but antagonistic effects for foaming properties were noted.     

热处理对鸡蛋蛋黄性质的影响

研究了不同强度的热处理(处理温度59、62、65、68℃,处理时间0～9 min)对鸡蛋蛋黄上清和颗粒的蛋白质组成、溶解性、乳化性和游离巯基含量的影响。结果表明:蛋黄上清中的γ-卵黄蛋白和蛋黄颗粒中的部分高密度脂蛋白在加热处理过程中发生变性形成大分子聚集体,加热处理对蛋黄上清蛋白质溶解度的影响大于对蛋黄颗粒的影响,温和的热处理对蛋黄上清与颗粒的乳化性质均没有显著影响,68℃处理较长时间会使蛋黄上清与颗粒的乳化活力下降,乳化稳定性提高。热处理过程中蛋黄上清和颗粒的游离巯基含量变化均未表现出明显的规律性。     

Physicochemical properties of leftover egg yolk after livetins removal

Isolation of immunoglobulin Y (IgY) from egg yolk using water-dilution method generates large quantities of leftover pellet as the co-product. Although egg yolk is well known for its great emulsion property, there is a lack of understanding on how livetins removal would affect the emulsion and rheological properties of the pellet. Therefore, the objective of this study was to determine the effect of soluble protein removal on emulsifying and rheological characteristics of the leftover egg yolk. Egg yolk pellet exhibited distinct structural and physicochemical properties after soluble protein removal. Emulsions prepared from pellet were more vulnerable to coalescence instability than that of egg yolk, although both had a similar oil droplet size. Egg yolk displayed a Newtonian behaviour, compared to a shear-thinning behaviour of pellet. Pellet showed a higher apparent viscosity as well as higher viscoelastic moduli than those of egg yolk, probably due to increased hydrogen bond and hydrophobic interactions in the pellet. Therefore, the changes on the emulsion stability and the rheological properties of egg yolk after soluble proteins removal should be considered in food formulation and processing. Further study is needed to improve the emulsion property of pellet for uses in the food industry.     

Characterisation of emulsion properties and of interface composition in O/W emulsions prepared with hen egg yolk, plasma and granules

Comprehension of hen egg yolk emulsifying properties remains incomplete because competition between its various emulsifiers (proteins and lipoproteins containing phospholipids) has not been clearly elucidated and colloidal interactions between yolk-stabilised oil droplets have not been documented. Recent studies emphasised the interest of the fractionation of yolk into plasma and granules to improve this comprehension. In the present study, we characterised, concurrently, emulsion properties (oil droplet size and stability against creaming) and interface attributes (interfacial concentrations of proteins and phospholipids, SDS-PAGE profiles of adsorbed proteins and zeta potential) in oil-in-water (O/W) emulsions prepared with yolk, plasma and granules. We observed these features at four physicochemical conditions (pH 3.0 or 7.0 and at 0.15 or 0.55 M NaCl). Emulsion properties in emulsions made with yolk or plasma varied similarly as a function of pH and NaCl concentration whereas granules emulsions exhibited distinct properties. Therefore the main contributors to yolk emulsifying properties are to be sought for among plasma constituents (proteinaceous or phospholipids). Since, in plasma emulsions, variations of emulsion stability against creaming correlated exclusively to variations of protein interfacial concentration, a driving contribution of the proteinaceous part of plasma, namely apo-LDL, was hypothesised. In the pH and ionic strength ranges studied, zeta potentials of the interfaces were low, excluding extended electrostatic repulsion between oil droplets. We deduced that steric repulsion is the main interaction opposing to droplet aggregation in food emulsions made with yolk.     

Thermal and Functional Properties of Bovine Blood Plasma and Egg White Proteins

All blood plasma proteins denatured at lower temperatures than the major protein of egg white (ovalbumin). γ-Globulin was the most heat-stable, and fibrinogen was the most heat-sensitive protein of blood plasma. The plasma had similar foaming capacity as egg white, but foam stability of plasma was less. Among plasma fractions, serum albumin, fibrinogen, and α-globulin had good foaming capacities and stabilities. Globulins were the only protein fraction of egg white with good foaming properties. Blood plasma and its component proteins were better emulsifiers than egg white and its component proteins.     

White lupin protein isolate as a foaming agent

 In this work the foaming ability of white lupin protein isolates was investigated in order to evaluate the potential use of these isolates as functional additives in food products and to find a vegetable alternative to egg-white foams. Lupinus albus protein isolate, modified in order to improve its foaming ability, was tested. Thermal denaturation, chemical treatment (acylation) and enzymatic hydrolysis (with vegetal proteases) were used, and the best results were obtained by using an optimised thermal denaturation method. A series of additives was tried out in order to further improve foam stability; xanthan gum gave the best results. Prior heat treatment of the protein and the conditions under which foam was generated were optimised using response surface methodology. Texture and microstructure of the optimised lupin foam were objectively evaluated. The lupin foam, when boiled in water for 5 min became very similar in texture and microstructure to uncooked egg-white foams. This shows, therefore, some promise as a substitute of the latter for products like fruit and chocolate "mousses", with the advantage of being able to withstand heat treatments. Received: 30 October 1997 / Revised version: 21 January 1998     

湿热-胶体改性对小麦面筋蛋白功能性质的影响

研究了在湿热条件下将羧甲基纤维素钠(CMC)、明胶、海藻酸钠、果胶、瓜尔胶这几种不同胶体作为添加剂添加到小麦面筋蛋白中,测定了其对小麦面筋蛋白功能性质的影响,主要以小麦面筋蛋白的粘稠性、乳化性和乳化稳定性、溶解性、起泡性这几个指标作为参考。实验结果表明,与简单混合相比,羧甲基纤维素钠、明胶、海藻酸钠、果胶在湿热条件下使小麦面筋蛋白的溶解性,乳化性和粘稠性都有一定幅度的提高,但是对小麦起泡性和乳化稳定性的影响不大;瓜尔胶在湿热条件下对小麦蛋白性质的影响与简单混合相比基本持平。     

Characterization of Phase Separation Behavior, Emulsion Stability, Rheology, and Microstructure of Egg White–Polysaccharide Mixtures

ABSTRACT:  Phase separation behavior of egg white-pectin/guar gum mixtures was investigated. These systems led to phase separation arisen by either depletion flocculation or thermodynamic incompatibility. The influence of polysaccharides on the emulsifying activity index (EAI), emulsifying stability index (ESI), creaming stability, microstructure, and rheological properties was also studied at different polysaccharide concentrations (0% to 0.5%, [w/v]). Increasing pectin and guar gum concentration from 0.01% to 0.5% significantly improved EAI by 51% and 25%, respectively. The highest ESI and EAI values were obtained in the presence of 0.5% (w/v) pectin/guar gum. Microscopic images showed that emulsions containing polysaccharides had small droplets as compared to that of emulsions without polysaccharides. The addition of polysaccharides improved emulsion stability against creaming. Egg white-stabilized emulsions with and without polysaccharides reflect the pseudoplastic behavior with  n  < 1.0. Polysaccharides, especially at high concentrations, affected the viscoelastic behavior of the emulsions; storage ( G ') and loss modulus ( G ") crossed-over at lower frequency values as compared to that of emulsions containing no polysaccharide.     

Continuous centrifugal fractionation of egg yolk granules and plasma constituents influenced by process conditions and product characteristics

The egg yolk main fractions, granules and plasma, show considerable different emulsifying properties. In order to use this potential, the present study investigates the influence of variable process conditions on the continuous centrifugal separation process of liquid egg yolk. It is shown that the granule fraction represents no homogeneous component, but consists of three different subfractions with different size, density and structure. It was confirmed by SDS–PAGE that each granule subfraction incorporated different amounts of LDL. The inhomogeneity leads to a subfraction depending sedimentation behaviour of the whole granule-fraction in egg yolk which could be clearly classified. Based on these findings, the impact of variable rheological properties on the sedimentation behaviour of polydisperse suspensions with high particle concentrations is discussed. However, fluid temperatures of 50 °C, a dry matter reduction below 29% prior to the centrifugal fractionation and g-forces up to 10,000g resulted in excellent separation efficiencies of the granule-fraction.     

亲水胶体对鸡蛋清起泡性的影响

亲水胶体在许多食品的制作过程中都起到重要的提升产品品质的作用。研究分析了黄原胶、海藻酸钠、羧甲基纤维素(CMC)、瓜尔豆胶和壳聚糖等几种亲水胶体的不同添加量对鸡蛋清的打擦度、起泡性及泡沫稳定性的影响。结果表明亲水胶体添加CMC、瓜尔豆胶可明显增加蛋清的打擦度,添加海藻酸钠则降低蛋清的打擦度,而黄原胶的添加对蛋清打擦度的影响则受到不同的添加量分别出现打擦度增加和降低的不同结果,壳聚糖的添加对蛋清的打擦度影响不大。研究过程也发现,蛋清中添加黄原胶、CMC、瓜尔豆胶和壳聚糖后,泡沫达到最大体积的时间比对照组明显缩短,蛋清起泡效率提高。几种胶体的添加增加蛋清打擦度由大到小顺序为:瓜尔胶>CMC>壳聚糖≈对照(无添加)>黄原胶>海藻酸钠。添加亲水胶体可以增强鸡蛋清的泡沫稳定性。     

Enthalpy of Denaturation and Surface Functional Properties of Heated Egg White Proteins in the Dry State

The enthalpy of denaturation (ΔH) and surface properties of proteins were related to elucidate the mechanisms of foaming and emulsifying properties by using various heated egg white proteins in the dry state. Foaming and emulsifying properties of all sample proteins were greatly increased with a decrease in the enthalpy of denaturation as determined by differential scanning calorimetry analysis. In plots, foaming and emulsifying properties correlated linearly with ΔH values for various dry-heated egg white proteins. Thus, the enthalpy of denaturation of proteins seemed to be a significant structural factor governing surface functional properties.     

Impact of a thermal treatment on the emulsifying properties of egg yolk. Part 2: Effect of the environmental conditions

The protein solubility and emulsifying properties of native and heat-treated egg yolk (EY) suspensions were investigated in various environmental conditions. Four distinct conditions were tested by combining two levels of pH, namely pH 4.0 and 6.5, and two levels of ionic strength, namely 0.15 and 0.52 M NaCl, in a model oil-in-water (O/W) emulsion containing 30% oil (v/v). Although the protein solubility was greatly reduced by the thermal denaturation in all tested environmental conditions, the average size of oil droplets obtained in emulsions made with heated EY was observed to be either similar or slightly smaller than that obtained with native EY, depending on the environmental conditions. Using heat-treated EY rather than native EY led to a significant increase of the interfacial protein concentration in all environmental conditions. This increased interfacial protein concentration was shown to have a major impact on the flocculation behaviour of the emulsions, as well as on their rheological properties and stability to creaming. Hypotheses regarding the mechanisms by which insoluble protein aggregates stabilise O/W emulsions at various pH and ionic strengths are discussed.