Metallic Cations Affect Functional Performance of Spray-Dried Heat-Treated Egg White

The functional performance of four metallic cations (Cu⁺⁺, Al⁺⁺⁺, Fe⁺⁺⁺, Zn⁺⁺) in spray-dried, heat-treated egg white were evaluated. Cu⁺⁺ excelled in all functional categories involving foams and angel food cakes. Zn⁺⁺ was least effective. These data suggest that Cu⁺⁺ would be a suitable additive to spray-dried egg white systems.     

Texture and Microstructure of Heat-Formed Egg White Gels

Egg white gels were formed by heating liquid egg white at various pH, protein, and NaCl levels at different temperatures and times of heating. Hardness, cohesiveness, and springiness of gels were measured. Serum was expressed from gels and evaluated by polyacrylamide gel electrophoresis. Selected samples were prepared for scanning electron microscopy. Gel hardness rose with increasing temperature, time, pH, and protein level, and decreased with added salt. Cohesiveness and springiness increased with time and temperature of heating. Expressed serum decreased as pH, time, temperature, and protein level were increased. Gels at pH 5 and 6 had a coarse, aggregated structure. At pH 9 protein strands and globules were arranged in a uniform matrix. Salt prompted aggregation of gels.     

不同热处理方式对卤蛋蛋白的质构影响

通过TPA方法与感官评价方法,研究了卤蛋加工过程中预煮时间、卤制时间、灭菌方式及时间对卤蛋蛋白的质构影响,发现卤蛋蛋白硬度受预煮时间、卤制时间影响显著;弹性、胶着性受卤制时间影响显著;黏性受高压灭菌时间影响显著。并选择出了较优的热处理方式:以15枚鸡蛋为一组,预煮15 min,卤制1 h、放置1 h、二次卤制1 h,121℃灭菌5 min。     

热改性蛋清粉的贮藏稳定性

为了解热改性蛋清粉的贮藏稳定性,文中对室温贮藏(12个月)的热改性蛋清蛋白功能性和分子特点进行了分析。研究表明:在贮藏期热改性蛋清粉的凝胶性、乳化性、泡沫性都有不同程度的降低,同时疏水性、巯基含量和分子柔性也有明显变化。相关性分析表明:热改性蛋清粉功能性的下降与分子结构的变化显著(P<0.05)相关。蛋白质分子特点是影响热改性蛋清粉的贮藏稳定性主要因素。     

Comparisons on the Functional Properties and Antioxidant Activity of Spray-Dried and Freeze-Dried Egg White Protein Hydrolysate

Freeze-dried and spray-dried egg white protein hydrolysates (FD-EWPH, SD-EWPH) prepared by papain were evaluated for their proximate composition, color, molecular weight distribution, physical structures, functional properties, and antioxidant activity. FD-EWPH and SD-EWPH had similar proximate composition and molecular weight distribution, but they had different color and physical structures. There was no significant difference (P > 0.05) in solubility among egg white protein hydrolysate (EWPH) before drying (UD-EWPH), FD-EWPH, and SD-EWPH. The foaming properties of EWPH were improved by freeze-drying but reduced by spray-drying (P < 0.05). Freeze-drying did not influence the emulsifying properties of EWPH while spray-drying had harmful effects on it. In the antioxidant test, no significant differences (P > 0.05) in 1,1-diphenyl-2-picryl-hydrazyl radical-scavenging activity, reducing power, and lipid peroxidation inhibition was found among UD-EWPH, FD-EWPH, and SD-EWPH. The results indicated that spray-drying might be suitable to dry antioxidant hydrolysates for its simple, cost-effective, and time-saving process. Moreover, further modeling study of optimized spray-drying processing parameters is needed in order to minimize the emulsifying and foaming property damage.     

鸭蛋清蛋白凝胶质构特性影响因素研究

以冻干鸭蛋清蛋白粉为原料,以凝胶硬度和弹性为指标,在探究鸭蛋清蛋白凝胶形成条件的基础上,考察金属离子对凝胶质构特性的影响。结果表明,鸭蛋清蛋白凝胶形成的最佳条件为：蛋清蛋白质量分数12.0%、pH 8.0、80 ℃加热40 min。不同浓度钠离子和钙离子对凝胶弹性的提高均有显著作用,高浓度钾离子作用不显著,镁离子、锌离子和亚铁离子的浓度较大时反而有抑制作用。镁离子对凝胶硬度增加有显著作用,钾离子无显著影响,钠离子和钙离子为先促进后稳定的趋势,锌离子和亚铁离子对凝胶硬度增加有抑制作用。     

Gelation of Egg White Proteins as Affected by Combined Heating and Freezing

Combined effects of preheating (60°C, 0 ～ 30 min) and freezing (– 10 or –20°C, 20 hr) on the gelation of dried egg white induced by reheating (80°C, 30 min) were examined in comparison with those of refrigerating (5°C, 20 hr). Refrigeration consistently induced harder gels, while freezing resulted in either harder or softer gels. Results of soluble protein content, turbidity, SDS-PAGE and gel filtration indicated that the unfolded and aggregated levels of ovotransferrin, caused by the cooperative effects of preheating and freezing or refrigerating, mainly determined the characteristics of gel properties.     

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.     

High-Resolution NMR Detection of Cholesterol Oxides in Spray-Dried Egg Yolk

A new approach, alternative to currently available methods, for studying cholesterol oxidation in egg powder is reported. The quantitative analysis of cholesterol oxides was carried out by high-resolution proton nuclear magnetic resonance (¹H-NMR). The following oxides were isolated from spray-dried egg powder by rapid chromatographic procedures and detected by selecting “marker”¹H-NMR signals: 7-ke-tocholesterol, 7α-hydroxy-cholesterol, 7β-hydroxy-cholesterol, cholesterol-α-epoxide and cholesterol-β-epoxide. The quantified cholesterol derivatives ranged from 4.9 to 9.1 ppm with a detection limit of 0.3 ppm (5 μ.g from 16g of matrix). The main usefulness of the method should be in investigating intermediates and products due to chemical transformation of cholesterol during storage and heating of foodstuffs.     

Effects of Yolk Contamination, Shearing, and Heating on Foaming Properties of Fresh Egg White

ABSTRACT:  A series of experiments were conducted to evaluate effects of yolk contamination, shearing, and thermal treatment on foaming properties of liquid egg white. Samples obtained from industrial processing were also evaluated. Whipping and purging methods were both used to assess their effectiveness and sensitivity in evaluating foaming. A concentration as low as 0.022% (as-is basis) of yolk contamination caused significant reductions in foaming capacity and foaming speed. The neutral lipid fraction of egg yolk caused the major detrimental effect on foaming, and phospholipids fraction did not give significant foaming reduction at a concentration as high as 0.1%. High-speed and short-time shearing caused no apparent damage but longer shearing time significantly impaired foaming. Heat-induced foaming change is a function of temperature and holding time. Foaming was significantly reduced at a temperature of 55 °C for 10 min, whereas it did not change up to 3 min at a heating temperature of 62 to 64 °C. Industrial processing steps (pumping, pipe transfer, and storage) did not produce negative effects on foaming of the final products and the controlled pasteurization was actually beneficial for good foaming performance. Therefore, yolk contamination of the egg white was the major factor in reducing foaming properties of the white protein.     

蛋清利用研究进展

在食品行业中,蛋黄的需求量较大,而蛋清常常作为废弃物被丢弃,这既造成了环境污染,也浪费了宝贵的蛋白质资源,因此亟需开展蛋清的综合利用研究。目前国内外对蛋清研究的热点主要集中在溶菌酶的提取方法、蛋清的冷杀菌技术、蛋清的功能性质以及蛋清的酶水解物生物活性4 个方面,因此本文从这4 个方面综述了近年来对蛋清利用的研究进展。     

蛋清蛋白质水解物的精制

蛋清蛋白质水解液含盐量高，风味欠佳。本研究用离子交换树脂对蛋清蛋白质水解液进行脱盐处理，在10倍柱体积/h的流速下，氮回收率为87％，脱盐率可达90％以上。实验结果还表明，水解液在温度高于50℃时有明显异味，β－环状糊精能有效改善产品的风味。     

咸蛋真空腌制过程中蛋清的理化性质变化

该研究通过真空减压腌制设备常温下加工咸蛋,采用核磁共振法、荧光法、凯式定氮法、凝胶电泳法等,考察在此过程中浓厚蛋白与稀薄蛋白的理化性质变化.结果表明,新鲜鸭蛋腌制后蛋清指数明显下降,与稀薄蛋白相比,浓厚蛋白中自由水含量少而结合水含量多.与新鲜鸭蛋的蛋清相比,浓厚蛋白、稀薄蛋白的表面疏水性都增加,总巯基和自由巯基都显著降...     

Gel Strength Development During Heating of Surimi in Combination with Egg White or Whey Protein Concentrate

Gel strengths (work of penetration) of surimi (refined minced fish, MF) alone and in combination with egg white or whey protein concentrate were periodically measured by an annular pump during constant rate heating. Combination gels containing low percentages of MF were of a lesser strength than an additive relationship would have predicted. However, the strength of gels containing greater percentages of MF did relate to the gel strengths of the uncombined proteins.     

Morphology and Texture of Bologna Sausage as Related to Content of Fat, Starch and Egg White

The effects of fat (7.0, 14.0 and 20.0%), starch (0, 5 and 10%) and egg white (0, 1.5 and 3%) on the microstructure and texture of bologna sausages were examined. As levels of fat and starch increased, the microstructure exhibited increasing numbers of holes (P<0.05), smaller in size (P<0.05) and similar (P>0.05) in shape. No clear relationship was found between addition of egg white and these morphological variations. Low-fat sausage (7.0%) was less hard and chewy (P<0.05) than high-fat (20.0%) sausage; likewise, a direct relationship was found between starch and egg white content and hardness and chewiness of the bologna.     

基于差示扫描量热法研究喷雾干燥鸡蛋全粉热转变温度

研究含非冻结水（较低水分含量）喷雾干燥鸡蛋全粉与含冻结水（较高水分含量）样品的热转变温度,以及鸡蛋全粉的吸附等温线,为蛋制品干燥或冷冻加工的稳定性提供数据支持。采用差示扫描量热仪检测样品,结果发现含非冻结水样品中有两个吸热峰,分别是卵转铁蛋白和卵白蛋白的变性峰,二者的变性温度（Td）都随湿基水分含量的增大而减小。对于含冻结水的样品,冻结温度（TF）与湿基水分含量之间的关系采用Clausius-Clapeyron方程描述,由冰晶熔融焓值得到非冻结水的湿基水分含量为0.18 g/g,再通过Clausius-Clapeyron方程得到其对应的冻结终点温度（Tm’）为－14.6 ℃。只有当湿基水分含量为0.22 g/g时,才检测到其玻璃化转变温度（－46.3 ℃）。此外,还研究了喷雾干燥鸡蛋全粉的吸附等温线,采用GAB模型进行非线性拟合,结果表明鸡蛋的吸附等温线为II型,其单分子层干基水分含量为0.043 g/g。本研究结果能为蛋制品的最适干燥或冷冻加工条件提供理论依据。     

Clarification of Spray-Dried Egg Yolk Suspensions and Solubilization of Proteins from Lipoproteins

The separation of proteins and lipids from spray-dried egg yolk was attempted using commerical enzymes and mold enzymes. Good solubilization of protein from a spray-dried egg yolk suspension (clarification of the suspension), could not be obtained with purified commercial enzymes (protease, lipase and phospholipase), but three crude enzymes extracted from molds and one commercial enzyme produced good results. Among them, Newlase F (crude preparation, derived from the genus Rhizopus) successfully clarified the spray-dried egg yolk suspension (pH 4.7, 40°C, 5–8 hr), thereby solubilizing about 85% of the total protein in the whole spray-dried egg yolk.     

Effect of the Controlled High-Intensity Ultrasound on Improving Functionality and Structural Changes of Egg White Proteins

The objective of this research was to investigate the impact of high-intensity ultrasound (HIU) generated by a probe-type sonicator (frequency 20 ± 0.2 kHz and an amplitude of 40%) for 2–20 min on the selected functional and structural properties of egg white proteins (EWPs) and their susceptibility to hydrolysis by alcalase. The protein solubility, foaming, and emulsifying properties were studied as a function of ultrasonication time and related to protein particle and structural properties. The length of ultrasonication exhibited important effect on EWP particle size, uniformity, and charge, affecting also the protein conformation and susceptibility to alcalase hydrolysis and determining functional properties. There was a linear correlation between the particle size decrease and the solubility while a two-step linear correlation between the foam capacity (FC)/foam stability (FS) and particle size was apparent. Specifically, FC and FS sharply increased with decreasing particle size for range from ～370 to ～260 nm, and below this range from 260.6 to 68.4 nm, the changes were not that substantial. Besides, the solubility, FC, and FS were directly and linearly related with the absolute value of the particle zeta potential. The overall emulsifying properties were also improved with an increase of sonication time, through both the decrease of the mean particle diameter and the increase of zeta potential, but there was no direct correlation between the emulsion activity/stability index and protein particle size and/or charge. Analysis of EWP structure by Raman spectroscopy revealed that the HIU leads to changes in the secondary structure, while heat and ultrasound generated by the ultrasound bath were not sufficient to exhibit this effect.

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Graphical abstract

     

Sulfhydryl Groups Changes in Heat-induced Soluble Egg White Aggregates in Relation to Molecular Size

The sulfhydryl content of heat-induced soluble egg white aggregates gradually decreased in proportion to standing time at room temperature, and the molecular size of the aggregates continued to increase at least 4 days. The progress of soluble egg white aggregates was much inhibited by N-ethylmaleimide. Soluble egg white aggregates are polymerized through a mechanism involving sulfhydryl-disulfide interchange and sulfhydryl oxidation during standing.