RHEOLOGY OF SALTED EGG YOLK

The influence of salt content (7-14% of weight) on the rheological behaviour of egg yolk in the temperature range 5-60°C was studied. The samples showed rheological behaviour that may be described by the power law equation. An increase in the salt content leads to an increase in the consistency index, whereas the flow behavior index shows a tendency to decrease. The effect of temperature on the consistency may be related by an Arrhenius-type equation in which the activation energy decreases as the salt content increases. The behaviour index does not vary greatly with temperature and there is a linear relation with the total solids content. A general equation describes the behaviour of egg yolk for the ranges of dry extract (D), salt content (C) and temperature studied:
     

COLORIMETRIC CHARACTERIZATION OF EGG YOLK AND EGG YOLK PRODUCTS

Procedures are suggested for COLOR-EYE® evaluation of various yolk forms and products. Chromaticity coordinates derived from COLOR-EYE determinations and the calculated dominant wavelength (λ_d), excitation purity (P_e) and luminous reflectance (Y_CIE) values were also determined for each yolk form and product analyzed. Characteristics of aged yolks included reduced λ_d and P_e and an increase in Y_CIE values; the greatest effects were at the highest levels of pigmentation concentration. Luminous reflectance values were substantially lowered by the addition of sugar and subsequent frozen storage; all other calorimetric criteria were relatively unchanged. Yolk age effects were negligible for the calorimetric characterization of yolks incorporated into product forms. Mayonnaise products provided the most consistent COLOR-EYE readings. These data suggest the feasibility of utilizing the COLOR-EYE, or similar instrumentation, as an objective method for the color characterization of various yolk products. Numerous options are available for converting data into other desired instrumentation values and terminology.     

REFLECTANCE COLORIMETRIC EVALUATION OF EGG YOLK PIGMENTATION

Moderately pigmented yolks were diluted with pigment-free yolks to provide a wide range of samples with which to compare standard beta carotene equivalents with excitation purity and luminous reflectance values obtained with a reflectance calorimeter. Pigmented yolks were also mixed with a white diluent for reflectance colorimetric comparisons. Correlation coefficients of beta carotene equivalents with excitation purity and luminous reflectance values were +0.906 and −0.874, respectively. The regression line for luminous reflectance was linear and for excitation purity was curvilinear. The white diluent (1:l ratio) resulted in significant reduction of the tendency of excitation purity to plateau for deeply pigmented yolks.     

IDENTIFICATION OF GANGLIOSIDES AS CONSTITUENTS OF EGG YOLK

Gangliosides were identified as constituents of the lipid fraction from egg yolk. Approximately 0.07 mμmole of ganglioside sialic acid was recovered per gram wet weight of yolk. Thin-layer chromatographic separation revealed the presence of at least eight separate ganglioside species in this fraction. Glucose, galactose, hexosamine and sialic acid, in the molar proportions of 1.00 to 1.25 to 1.95 to 1.19, were the major carbohydrates of yolk ganglioside fractions. Fourteen fatty acids were observed in the ganglioside fraction; 16:0 (26.6%) 18:0 (9.2%), 18:l (22.9%) and 22:0 (28.3%) were predominant.     

CLARIFICATION OF EGG YOLK SUSPENSION FOR THE PRODUCTION OF N-ACETYLNEURAMINIC ACID

Several filter aids were investigated in order to separate the hydrolyzed egg yolk suspension easily. λ-Carrageenan was found to be the most effective flocculant for the purpose. The addition of 1.67 g λ-carrageenan to 1 L of hydrolyzed egg yolk suspension was effective to get a clear supernatant. The ionic flocculation between the λ-carrageenan and the egg yolk lipoprotein was presumed. Using λ-carrageenan, N-acetylneuraminic acid containing in the hydrolyzed delipidated egg yolk was prepared. λ-Carrageenan did not adsorb to an anion exchange resin and could be separated completely from N-acetylneuraminic acid, when the filtrate treated with λ-carrageenan was applied on a column of the resin.     

RHEOLOGY OF FRESH, AGED AND GAMMA-IRRADIATED EGG WHITE

SUMMARY– Rheology of unmixed egg white at 2°C was studied with a narrow-gapped rotational viscometer over a 20-fold range of shear rates. For a constant shear rate, egg white consistency decreases with time and approaches an equilibrium value in a few minutes. Flow behavior is pseudoplastic at 2°C between shear rates of 8.1–147 sec^-1 and the shear stress-shear rate relation is accurately described by the power law and Casson models. The effects of gamma irradiation dose on Haugh unit score and equilibrium shear stress are discussed.     

磷脂酶A改性的蛋黄功能性质及其对蛋制品品质影响

采用磷脂酶A水解蛋黄中的卵磷脂生成溶血卵磷脂，转化度为80％。研究了磷脂酶A改性蛋黄的功能性质及其对蛋黄酱和面包品质的影响。改性蛋黄功能性实验表明：酶法改性之后的蛋黄比普通蛋黄具有更大的乳化稳定性、吸湿性，以及显著的耐热性。蛋黄酱应用实验表明：相对普通蛋黄制作的蛋黄酱，酶法改性的蛋黄制作的蛋黄酱黏度是其1．5倍，而且改性蛋黄制作的蛋黄酱可经受100℃，30min的热处理而不会有油析出。面包应用实验表明：改性蛋黄制作的面包具有更高的综合评分，比普通蛋黄对面包具有更好的抗老化效果。     

INFLUENCE OF EGG YOLK LIPOPROTEINS ON THE RHEOLOGY AND STABILITY OF O/W EMULSIONS AND MAYONNAISE 1. VISCOELASTICITY OF GROUNDNUT OIL-IN-WATER EMULSIONS AND MAYONNAISE

Viscoelastic properties of groundnut oil-in-water emulsions stabilized by egg yolk and of mayonnaise have been deduced from their creep compliance-time response to a constant low shear stress. The viscoelastic parameter values, emulsion stability and initial mean drop size were influenced by pH and NaCl, due to disruption of the egg yolk components. When carboxymethylcellulose was incorporated in the continuous phase of the O/W emulsions an egg yolk-carboxymethylcellulose complex was formed and this affected the rheological properties of the emulsions and also their stability. Mayonnaises exhibited more pronounced viscoelasticity and greater stability than the O/W emulsions. At elevated temperature the micelles adsorbed around oil drops degrade. Their lipoprotein structure unfolds so that more segments on adjacent drops are then available for interlinking and network formation.     

THE LIPIDS OF EGG YOLK. 5. Presence of Ceramide

SUMMARY —Ceramide (an N-acyl sphingosine) was isolated from egg yolk lipid and examined for composition of fatty acids and long-chain base constituents. Yolk ceramide was observed to contain sixteen fatty acids; C _24:0 (35.7%), C _22:0 (22.7%), C _23:0 (15.1%) and C _24:1 (13.5%) were predominant. The component long-chain bases were identified as sphingosine and dihydrosphingosine, the former being the major component (88.6%).     

AN IMPROVED METHOD OF CHOLESTEROL DETERMINATION IN EGG YOLK BY HPLC

An improved method for cholesterol determination in egg yolk is reported in this paper. Egg yolk was first diluted. Cholesterol was then extracted with ether and petroleum ether, and quantified by reverse phase chromatography on a Zorbax ODS column (0.46 × 15cm, 5–6 μm) using a mobile phase of acetonitrile and 2-propanol (4:1) with a flow rate of 0.6 mL/min. A linear correlation was observed between cholesterol concentration at 0.05–0.40 mg/mL and its peak heights with a correlation coefficient of 0.9993 (n = 5). The average recovery was 98.9%, and detection limit was 0.02 mg/mL. No differences in cholesterol concentration were observed between egg yolk samples with and without saponification. Rapid and reproducible quantification of cholesterol in egg yolk can be completed with this simplified method.