Structural and foaming properties of egg albumen subjected to different pH-treatments in the presence of calcium ions

The influence of low (pH 1.5–3.5) and high (10.5–12.5) pH-induced unfolding followed by refolding to pH 4.5–8.5 in the presence of Ca²⁺ on the structural, functional and viscoelastic properties of egg albumen was investigated. pH-induced unfolding significantly improved overrun, stability and reduced liquid drainage of egg albumen for most pH-treatments compared to untreated control. Unfolding at pH 12.5 led to the largest improvements, overall. Improvements in foam overrun and stability were found to be mostly due to pH-treatments, with Ca²⁺ having a small effect when compared to prior studies. Inclusion of Ca²⁺ did however reduce liquid drainage, and was found to significantly modify the rheological properties of the foams, making them stiffer and stronger. Inclusion of Ca²⁺ during pH-treatment led to more exposed –SH groups compared to albumen pH-treated in its absence. The pH-treatments also produced albumens with higher surface hydrophobicity, which was determined mostly to come from the pH unfolding, with Ca²⁺ having little impact.     

Effect of ascorbic acid on the foaming and gelling of globular proteins

Foam expansion and foam stability of plasma and egg albumen proteins were enhanced in the presence of increasing concentrations of ascorbic acid (0.1–1.0%). BSA showed the greatest improvement in foaming properties following treatment with ascorbic acid, whilst foaming properties of egg albumen were improved to a limited extent. A combination of partial acid hydrolysis and treatment with 1% ascorbic acid was required to dramatically improve the foaming properties of bovine blood plasma. In the presence of sucrose, foam expansion of both native and ascorbic acid-treated blood plasma was decreased. In contrast the foam expansion of ascorbic acid-treated egg albumen was greater although this effect decreased slightly on incubation. the gelation of ascorbic acid treated proteins increased with increasing temperatures over 80–90°C, particularly for BSA and blood plasma, and with increasing concentrations of ascorbic acid. Ascorbic acid-treated proteins exhibited enhanced surface and exposed hydrophobicity and reduced numbers of sulphydryl groups indicating the involvement of these factors in foam and gel formation.     

超声处理对蛋清蛋白结构性质及蛋清液起泡性的影响

研究脉冲式超声处理对蛋清液拉曼光谱、内源性荧光光谱、静态流变学性质、粒径和理化结构的影响,结合起泡性的变化进行相关性分析。研究发现,超声处理能够改变蛋清蛋白二硫键构象,降低蛋清液黏度,减少总巯基含量,对无规卷曲、β-转角含量和酪氨酸残基峰强比（I850/I830）影响较小,蛋清液依旧为假塑性流体。在超声处理15 min内,蛋清蛋白质粒径、表面巯基含量、热变性焓（ΔH）、α-螺旋和β-折叠含量逐渐减少,内源性荧光强度和表面疏水性逐渐增强,色氨酸残基趋向于“暴露的”展开形式;起泡性得到改善,且泡沫体积小,呈均匀紧密的排列,泡沫稳定性小幅降低。随着超声时间的延长,β-折叠含量继续降低,粒径、表面巯基含量、ΔH、α-螺旋含量、色氨酸残基峰强比（I1 363/I1 338）、内源性荧光强度和表面疏水性呈现不同的变化趋势,起泡性逐渐降低,但泡沫稳定性有所升高。相关性分析表明,起泡性与I1 363/I1 338、表面疏水性呈正相关,与ΔH、平均粒径、α-螺旋含量和表面巯基含量呈负相关,泡沫稳定性与表面疏水性呈负相关。     

Rheological properties of foams generated from egg albumin after pH treatment

Rheological properties of foams at pH 4.5 and 8.5 made from egg albumin proteins after pH-induced unfolding and refolding treatments were investigated. The foams behaved as highly elastic materials. Static and dynamic yield stress was investigated using small, steady shear experiments. Yield stress was measured also in oscillation mode and high correlation was found between dynamic yield stress and critical stress amplitude. All pH treatments led to firmer foams than untreated foams at pH 8.5. At pH 8.5 the control foam had a very weak structure (static yield stress at 3.4 Pa and dynamic yield stress at 5.5 Pa for the fresh made foams), while pH-treated foams at pH 8.5 had values (static yield stress up to 39.2 Pa and dynamic yield stress up to 47.1 Pa for the fresh made foams) that were even higher than the values for the control at pH 4.5 (static yield stress at 22.4 Pa and dynamic yield stress at 25.4 Pa for the fresh made foams, which is a good foaming pH for egg albumin). It was shown that an increase in yield stress of foams after drainage is related to foam stability and liquid drainage. This study demonstrated that unfolding egg albumin at low or high pH followed by refolding leads to a substantial increase in foam firmness and gives the foam different properties than foams from untreated egg albumin.     

Effect of heat treatment on foaming properties of ostrich (Struthio camelus) egg white proteins

The effect of heat-treatment on foaming properties of ostrich albumen was investigated. At pH 7.5, coagulation of ovotransferrin (OT) resulted in minimum foaming capacity (FC) and maximum foam density (FD). While both exposure of sulfhydryl groups of ovalbumin (OV) and OT-OV interactions improved FC at lower pH, neither of them had beneficial effect on FC at pH 9. At pH 9, FC and FD were mildly affected by heat-treatment because of less aggregation of OT, then FC decreased due to covalent aggregates composed of ovomucin and OV, but at higher temperatures, higher level of OV unfolding resulted in enhanced FC.     

Modified Soy Proteins with Improved Foaming and Water Hydration Properties

Soy proteins were modified by alkali treatment at pH 10.0, followed by papain hydrolysis. Solubility, water hydration capacity (WHC), surface hydrophobicity, foaming and emulsifying properties of unmodified, alkali-treated, and papain-modified soy protein (PMSP) were compared. PMSP exhibited higher solubility (100% at pH > 7.0), WHC (3.13) and hydrophobicity (40.8) than unmodified soy protein which had solubility 68.5%, WHC 0.21, and hydrophobicity 8.1. The PMSP had foaming capacity (22.0 mL) similar to egg white (21.2 mL) at pH 7.0; and enhanced foam stability (36.4) compared to the unmodified control (32.9). In general, alkali-treated soy had lower functional properties. Emulsifying properties of PMSP and alkali treated soy were unchanged by the modification. PMSP could be used as an egg white substitute in foaming applications at neutral pH.     

高压脉冲电场(PEF)对蛋清蛋白功能特性的影响

蛋清蛋白不仅具有重要的营养价值,而且还具有重要的功能特性如乳化性、起泡性等,作为一种重要的蛋白原料,本实验研究了高压脉冲电场对蛋清蛋白功能性质的影响。结果表明:蛋清蛋白的溶解度在脉冲电场强度大于35kV/cm时下降;蛋清蛋白的乳化性、起泡能力、泡沫稳定性及疏水性先随脉冲电场强度增加而增大,但当脉冲电场强度大于30kV/cm后,蛋清蛋白的乳化性、起泡能力、泡沫稳定性及疏水性下降;随着脉冲电场数的增加,蛋清蛋白的溶解度、乳化性、起泡能力、泡沫稳定性及疏水性变化不显著。     

Simple pH treatment as an effective tool to improve the functional properties of ovomucin

Ovomucin has been considered to contribute a lot to the excellent functional properties of egg white. This work focused on investigating the effects of pH and protein concentration on foaming and emulsifying properties of ovomucin to evaluate the proper use of this egg protein as a functional food ingredient, and to clarify its contribution to the functional properties of egg white under different pH conditions. Protein solubility and surface hydrophobicity were measured through the pH ranged from 2.3 to 11.0. Alkali treatment gave ovomucin improved emulsification properties, which were correlated well with the surface hydrophobicity (r ≥ 0.89, P < 0.01). Although ovomucin showed lower foaming capacity in acid and neutral solution, enhanced foaming stability was observed with weak acid-treated ovomucin (pH 5 to 6) compared to native ovomucin. These results demonstrated that acid and alkali treatment, which leads to partial unfolding of ovomucin can improve functional properties of ovomucin, with the greatest improvement for emulsification properties being from the alkali treatment and for foaming stability being from weak acid treatment. These results are helpful to produce unfolding ovomucin suitable for wide range of applications in food industry, and to provide useful information on the proper use of egg white in different food systems. PRACTICAL APPLICATION: Ovomucin plays a critical functional role in egg white products. However, it is typically insoluble in distilled water or common salt solutions, which has thus limited its commercial applications. Alkaline treatment resulted in gradual increase in solubility, which markedly enhanced the emulsifying properties, on the other hand foaming stability of ovomucin can be promoted by weak acid treatment. The results of this work help to produce unfolding ovomucin suitable for wide range of applications in food industry, and to provide useful information on the proper use of egg white in different food systems.     

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.     

球磨处理对鸡蛋清蛋白结构、性质及起泡性的影响

蛋清因具有优良的起泡性而在焙烤等食品加工领域中被广泛应用,因此,提升蛋清蛋白的起泡性有重要意义。本实验对鸡蛋清蛋白进行球磨处理,通过测定球磨处理后蛋清蛋白的游离巯基含量、表面疏水性、水解度、Zeta-电位和粒径,并分析其热力学性质、二级结构、起泡特性和微观结构,以研究球磨处理对蛋清蛋白结构性质及其起泡性的影响。结果表明：球磨处理后的蛋清蛋白粉随处理时间的延长起泡性无明显变化,泡沫稳定性呈现先升高后降低的趋势,且在球磨处理40 min时达到最大值（33.5 s）,比对照组提高近3 倍;此外,球磨处理可显著降低蛋清蛋白表面疏水性和热变性焓（ΔH）（P＜0.05）,显著提高水解度和降低Zeta-电位绝对值（P＜0.05）,并增大粒径,但对游离巯基含量和变性温度无显著影响（P＞0.05）;随着球磨时间的延长,蛋清蛋白β-折叠结构相对含量显著升高（P＜0.05）,α-螺旋结构相对含量先降低后升高,而β-转角结构相对含量先升高后降低;扫描电子显微镜结果显示球磨处理使蛋清蛋白呈现出零散碎片化和絮状。综上,适度球磨处理可以改变蛋清蛋白分子结构,进而提升其泡沫稳定性。     

Influence of pH on surface properties of aqueous egg albumen solutions in relation to foaming behaviour

The surface properties of aqueous egg albumen protein solutions (0.1 g litre⁻¹) were studied at pH values of 4.8, 7.0, 9.2 and 10.7 and related to foaming behaviour such as bubble size distribution, overrun and drainage. By measurements far from equilibrium of dynamic steady state surface dilation using the overflowing cylinder technique, egg albumen showed ability to slow down surface expansion and to lower the dynamic surface tension. The pH‐effect was small, but at pH 4.8 the film length, at which a motionless surface was created, was longer than at higher pH indicating a somewhat more rigid surface at low pH. Near equilibrium sinusoidal surface area deformation resulted in relatively high moduli of egg albumen, with a significant effect of pH. The surface modulus E showed at pH 4.8 an increase in the course of time, but at higher pH it was constant. Large deformation of egg albumen surface was not destructive, and for all pH values the surface behaved viscoelastic, with highest loss modulus E″ and tan θ values at pH 4.8. Surface deformation frequency sweeps revealed the relaxation processes to be relatively slow at pH 4.8 and faster at pH 7.0–10.7. Foamability measured as overrun of foam as a result of shaking and stirring was highest at pH 4.8 and lowest at pH 10.7. Foam stability against drainage was best at pH 7.0 after 30 min, but at a long‐term scale foam at pH 4.8 was most resistant to drainage. Foam samples were subjected to microscopy and image analysis. The smallest bubbles were found at pH 4.8 (mean diameter 142 µm) and the largest at pH 7.0 (mean diameter 328 µm). In conclusion, the foaming behaviour of an aqueous egg albumen solution at pH 4.8 can be related to dynamic surface properties as follows: the more rigid behaviour of the surface at this pH favours a small bubble size and slow drainage of liquid from the foam. The high overrun at this pH can be explained by a lower dynamic surface tension, but also here film stability during foam making can be promoted by a more rigid liquid surface. © 1999 Society of Chemical Industry     

Functional Properties of Pork Liver Protein Fractions

The functional (emulsifying, gelling and foaming) properties of liver protein fractions as well as their molecular weight distribution and surface hydrophobicity were investigated and compared to commercial proteins. Two protein fractions were characterized: water soluble (WSLP) and WSLP combined with salt soluble liver proteins (W?+?SSLP). The effect of salt concentrations was also investigated (0, 1.8 and 3.4 % NaCl). Both WSLP and W?+?SSLP displayed good emulsifying properties and foam stability. However, their gelling properties were rather poor. An increase in salt concentration decreased the emulsifying properties of WSLP while the effect on W?+?SSLP was less pronounced. Addition of 1.8 % NaCl increased foaming ability of WSLP and W?+?SSLP while foam stability was not affected. Further increase of NaCl (3.4 %) decreased both foaming ability and foam stability and is probably attributed to refolding of the protein molecules because of the higher level of hydrophobic groups with 3.4 % NaCl. Gel forming ability of WSLP and W?+?SSLP containing 0 % was higher compared to high salt concentrations. However, higher salt concentrations shifted onset gelation temperature of WSLP and W?+?SSLP to lower temperatures probably due to partial unfolding of the proteins as indicated by an increase of the surface hydrophobicity.     

The significance of critical processing steps in the production of dried egg albumen powder on gel textural and foaming properties

The purpose of the present work was to study the variation in egg albumen functional properties as a function of seven selected processing steps from the initially raw liquid albumen to the final dried egg albumen powder. Albumen samples in six replicates were analysed for dry matter, pH, glucose, triglycerides, albumen gel properties (ie textural stress and Hencky strain, water‐ and protein‐binding capacity and gel colour L*, a*, b*), foaming properties (ie overrun, stability against drainage and bubble breakdown) and surface tension. The gel texture and water‐holding capacity significantly decreased during the processing steps from raw albumen through storage, centrifugation and ion exchange, whereas the final dry‐pasteurisation resulted in increased gel properties. Covalently linked protein polymers formed during the dry‐pasteurisation, as revealed by SDS‐PAGE, may explain this improvement. The foam overrun increased twofold during the three final steps of ultrafiltration, spray‐drying and dry‐pasteurisation compared with the raw albumen; however, the foam stability decreased, ie drainage and foam volume breakdown rates increased. The surface pressure increase was positively correlated with the foam overrun. This paper reveals at which processing steps the control of functional properties of egg albumen powder can take place. Copyright © 2004 Society of Chemical Industry     

干燥方式对蛋清蛋白理化性质和功能特性的影响

为探究干燥方式对蛋清蛋白（egg white protein,EWP）功能特性的影响及其内在机理,分别通过喷雾干燥与真空冷冻干燥制备蛋清蛋白粉,并对其蛋白结构、理化性质与功能特性进行研究。结果表明,与蛋清液（EWP-C）相比,喷雾干燥使蛋清蛋白（EWP-P）的内源性荧光强度降低,表面疏水性和表面游离巯基含量增大。傅里叶变换红外光谱分析显示,EWP-P的α-螺旋、β-折叠和β-转角分别为16.30%、25.72%和40.23%,冷冻干燥蛋清蛋白（EWP-D）分别为20.43%、24.32%和35.69%。不同pH下,EWP-D的溶解度均高于EWP-P,表面张力小于EWP-P。此外,EWP-P的接触角为99.62°,高于EWP-D（接触角为65.97°）,表明喷雾干燥能显著提高蛋白的疏水性（P<0.05）。EWP-D在不同pH下的乳化性、乳化稳定性以及起泡性均大于EWP-P,但起泡稳定性更小,这与EWP-D较高的溶解性与较低的表明疏水性有关。荧光倒置显微镜及激光共聚焦扫描显微镜分析表明EWP-D乳液的微粒更小,分布更均匀,其稳定性高于EWP-P。综上,喷雾干燥蛋清蛋白的β-折叠结构较多,表面游离巯基含量和表面疏水性较高,具有较好的凝胶性;冷冻干燥蛋清蛋白的表面疏水性较小,且表面张力小、溶解度大,具有更好的乳化能力与起泡性。     

The effect of instant green tea on the foaming and rheological properties of egg albumen proteins

The effects of three varieties of instant green tea (from China, Japan and Kenya) on the foaming and thermal properties of 1% (w/v) egg albumen and the gelation properties of 5 and 15% (w/v) egg albumen were investigated. All varieties produced similar effects on the foaming and gelation properties of egg albumen, but to different extents depending on the tea constituents. Mixtures of 1% (w/v) egg albumen and 0.25–0.4% (w/v) instant green teas in distilled water showed the greatest foam expansion (800–1140%) and foam stability (97–100%) at 10 min after whipping compared with 1% (w/v) egg albumen alone (226% for foam expansion and 34% for foam stability). Addition of instant green teas at levels above 0.5% (w/v) decreased foam expansion and stability. Small‐deformation rheology of mixtures of 5% (w/v) egg albumen and 1 or 2% (w/v) instant green teas showed an initial increase in elastic modulus (G′) and viscous modulus (G″) followed by a small, broad peak, indicating that the binding of tea constituents (polyphenols) with proteins may be reversible between 20 and 54 °C; this peak was not seen for 5% (w/v) egg albumen on its own. Large‐deformation rheological tests also indicated increased strength of mixed egg albumen/green tea gels with increasing levels of instant green teas. Differential scanning calorimetry thermograms showed that for the same instant green tea a higher concentration decreased the onset and peak (T_m) temperatures and enthalpy change values of all egg albumen protein peaks. Copyright © 2007 Society of Chemical Industry     

Influence of pasteurisation,freezing and storage on properties of egg products made from eggs stored for 7 and for 28 days

The influence of the age of eggs before breaking, pasteurisation, freezing and storage at —17°c and the method of whipping on the foaming power, foam stability and viscosity of liquid egg albumen and liquid whole egg were studied. The foaming power (relative volume of foam) and the foam stability were determined with the aid of a Hobart whipping machine N 50. The viscosity was measured with a Brookfield viscometer type LV. Liquid egg albumen from 28-day-old eggs had a better foaming power with better stability than that from 7-day-old eggs. The viscosity of the liquid egg albumen from 7-day-old eggs was higher than that from 28-day-old eggs. When pasteurised with aluminium sulphate, the foaming power and the foam stability of all liquid egg albumens increased. When pasteurised without aluminium sulphate, both properties increased for liquid egg albumen from 7-day-old eggs and decreased for that from 28-day-old eggs. During the first weeks of storage of the egg white at −17°C, the foaming power, foam stability and viscosity gradually increased. Whipping for 1 min at setting 2 and 2 mill at setting 3 yielded a higher foaming power and a higher stability of the foam than whipping for 1 min at setting 2 and then a few minutes at position 3 until visually the optimum had been reached. These differences were significant (P < 0·01) for the foaming power and foam stability. There was no significant difference between the foaming power and stability of the foam for liquid whole egg prepared from 7-day-old eggs and that from 28-day-old eggs. Pasteurisation (3 min at 65°c) gave a decrease in foaming power and foam stability and an increase in viscosity. These differences were significant (P < 0·07) for the foaming power and viscosity. Storage resulted in lower foaming power and higher foam stability. In this case, higher viscosity values were also obtained. The whipping method did not give any significant differences.     

Enhancement of Functional Properties of Rice Bran Proteins by High Pressure Treatment and Their Correlation with Surface Hydrophobicity

Changes in functional properties of rice bran proteins as influenced by high-pressure (HP) treatment (100–500 MPa, 10 min) were studied. Properties evaluated were protein solubility, water absorption capacity, oil absorption capacity, foaming capacity, foam stability, emulsifying activity, emulsion stability, least gelation concentration, and surface hydrophobicity. HP treatment at 100 and 200 MPa significantly improved the solubility and oil absorption capacity, while water absorption and foaming capacities increased further reaching the maximum at 500 MPa. Compared with the untreated control sample, the emulsifying activity and foam stability of treated samples were significantly higher and least gelation concentration was lower, but none of them showed any specific trend with pressure level. Emulsion stability and surface hydrophobicity increased with the pressure level until 400 MPa and decreased slightly at 500 MPa. Pearson correlation coefficients clearly showed that surface hydrophobicity was positively correlated with water absorption capacity, foaming capacity, emulsifying activity index, and emulsion stability index, but negatively correlated with least gelation concentration. The pressure treated rice bran protein possessed good functional properties for use as a food ingredient in the formulations.     

巯基乙醇对大豆分离蛋白热致聚合物界面性质的影响

为探讨β-巯基乙醇对大豆分离蛋白热致聚合物界面性质的影响,以大豆分离蛋白为原料,在pH7.0、90 ℃加热添加和不添加β-巯基乙醇（2 mmol/L）浓度为10 mg/mL的大豆分离蛋白溶液0 h和10 h,制备不同大豆分离蛋白质热致聚合物。观察了大豆分离蛋白、添加β-巯基乙醇大豆分离蛋白、大豆分离蛋白热致聚合物和β-巯基乙醇大豆分离蛋白热致聚合物的微观形态、游离巯基含量的变化,同时比较了起泡能力、泡沫稳定性、乳化活性、乳化稳定性、表面疏水性和浊度的差异。结果表明,大豆分离蛋白和添加β-巯基乙醇大豆分离蛋白呈现无规则状态,大豆分离蛋白热致聚合物为有规则的球状颗粒,而β-巯基乙醇大豆分离蛋白热致聚合物部分形成球状聚合物部分形成无规则聚合物。添加β-巯基乙醇改善了大豆分离蛋白的界面性质。与大豆分离蛋白相比较,添加β-巯基乙醇大豆分离蛋白和添加β-巯基乙醇大豆分离蛋白热致聚合物的起泡能力分别提高了64.56%和95.77%,乳化活性提高的幅度分别为12.94%和14.61%。添加β-巯基乙醇大豆分离蛋白和添加β-巯基乙醇大豆分离蛋白热致聚合物在长时间储藏中表现出良好的乳化稳定性和泡沫稳定性。这种良好的界面性质源于β-巯基乙醇的加入赋予聚合物具有更高的游离巯基含量和表面疏水性。并且本实验建立了4种样品的泡沫稳定性和乳化稳定性随时间变化的Rational函数和Linear函数经验模型,为大豆分离蛋白质的实际应用奠定了理论基础。     

Functional properties of raw and heat processed cashew nut (Anacardium occidentale, L.) kernel protein isolates

The functional properties viz. solubility, water and oil absorption, emulsifying and foaming capacities of the protein isolates prepared from raw and heat processed cashew nut kernels were evaluated. Protein solubility vs. pH profile showed the isoelectric point at pH 5 for both isolates. The isolate prepared from raw cashew nuts showed superior solubility at and above isoelectric point pH. The water and oil absorption capacities of the proteins were slightly improved by heat treatment of cashew nut kernels. The emulsifying capacity of the isolates showed solubility dependent behavior and was better for raw cashew nut protein isolate at pH 5 and above. However, heat treated cashew nut protein isolate presented better foaming capacity at pH 7 and 8 but both isolates showed extremely low foam stability as compared to that of egg albumin.     

pH值碱性偏移结合热处理对米糠蛋白结构和功能性质的影响

研究pH值碱性偏移（pH 11）结合热处理（50、60 ℃）对米糠蛋白结构和功能性质的影响。结果表明,pH值碱性偏移促使米糠蛋白二级结构由有序向无序转化,pH值碱性偏移结合热处理使得米糠蛋白二级结构呈现折叠-去折叠-复折叠的复杂变化,并伴随巯基氧化。pH值碱性偏移促使米糠蛋白展开,随着处理时间的延长,米糠蛋白重新聚集,热处理会加剧聚集程度。pH值碱性偏移使得米糠蛋白持水性、起泡性、泡沫稳定性、乳化性和乳化稳定性显著下降,仅持油性显著改善;随着处理时间的延长,米糠蛋白持水性、起泡性、乳化性和乳化稳定性逐渐上升,其中乳化性上升幅度最大。pH值碱性偏移结合热处理可显著改善米糠蛋白的持水性、起泡性、泡沫稳定性和乳化稳定性,同时也会降低米糠蛋白的持油性和乳化性。