Egg yolk protein

There is some evidence for chemically mediated endocrine disruption in amphibians. The egg yolk protein, vitellogenin, is inducible in amphibians by exposure to DDT. " Males of the short clawed toad Xenopus laevis given 250 fig/g or 1 fig/g o,p -DDT for seven days have been shown to produce vitellogenin, although the induction was less than that achieved by treatment with 1 fig/g of either 17/1-oestradiol or diethylstilboestrol. Research has also shown that endocrine disrupting chemicals can alter sex ratios in wild populations of certain species PCB congeners and organochlorine compounds have been linked with male domination of sex ratios in polluted compared to unpolluted sites. ... 

The phosphoprotein phosvitin may attach a large number of ferric ions/mole, according to Gray (99) [citing work of Saltman and Multani], the number bound may be as large as 46. Ferric ion, although firmly complexed, may be removed from this egg yolk protein by dialysis against solutions of ethylenediamine tetraacetic acid (102). 

A typical characteristic of many food products is that these are multi-phase products. The arrangement of the different phases leads to a microstructure that determines the properties of the product. Mayonnaise, for example, is an emulsion of about 80% oil in water, stabilized by egg yolk protein. The size of the oil droplets determines the rheology of the mayonnaise, and hence, the mouthfeel and the consumer liking. Ice cream is a product that consists of four phases. Figure 1 shows this structure schematically. Air bubbles are dispersed in a water matrix containing sugar molecules and ice crystals. The air bubbles are stabilized by partial coalesced fat droplets. The mouthfeel of ice cream is determined by a combination of the air bubble size, the fat droplet size and the ice crystal size. 

Lewis J.A., M.J. Clemens, and J.R. Tata (1976). Morphological and biochemical changes in the hepatic endoplasmic reticulum and golgi apparatus of male Xenopus laevis after induction of egg yolk protein s3mthesis by oestradiol-17 3. Molecular and Cellular Endocrinology 4 311-329. 

Precursor of egg-yolk proteins rich in carbohydrates, lipids, phosphates and calcium. It is the principal energy reserve in oocytes. Vg expression is under the control of estradiol-17(3 receptors. This protein complex is produced in the liver by oviparous vertebrates and used as a biomarker to detect environmental estrogens. Volume 1(14). 

Many food colloids are stabilized from proteins from milk or eggs [817]. Milk and cream, for example, are stabilized by milk proteins, such as casein micelles, which form a membrane around the oil (fat) droplets [817]. Mayonnaise, hollandaise, and bearnaise, for example, are O/W emulsions mainly stabilized by egg-yolk protein, which is a mixture of lipids (including lecithin), proteins, and lipoproteins [811,817]. The protein-covered oil (fat) droplets are stabilized by a combination of electrostatic and steric stabilization [817]. Alcohols may also be added, such as glycerol, propylene glycol, sorbitol, or sucrose sometimes these are modified by esterification or by... 

Casein or egg-yolk proteins are used as emulsifiers in a number of food products, such as O/W food emulsions (Table 13.1) [78,824]. A key difference here is that in caseinate-stabilized oil emulsions, the casein forms essentially monolayers and there are no casein micelles nor any calcium phosphate. Such emulsions are thought to be stabilized more by electrostatic repulsive forces and less by steric stabilization, in contrast to the situation in homogenized milk products [824]. 

Sauce bearnaise, for example, is an O/W emulsion that is mainly stabilized by egg-yolk protein in an aqueous phase of low pH. Perram et al. [830] describe how this system is primarily stabilized by electrostatic repulsive forces, and show how DLVO theory can be used to describe the effects of pH, surface charge, ionic strength, and temperature, on the stability of this emulsion. 

Awade, A.C. 1996. On hen egg fractionation Applications of liquid chromatography to the isolation and the purification of hen egg white and egg yolk proteins. Z Lebensm [Inters Forsch 202 1-14. 

Mine, Y. 1998. Emulsifying characterization of hen s egg yolk proteins in oil-in-water emulsions. Food Hydrocoil. 12, 409-415. 

Arukwe, A. and A. Goks0yr. Eggshell and egg yolk proteins in fish hepatic proteins for the next generation oogenetic, population, and evolutionary implications of endocrine disruption. Comp. Hepatol. 2 1-21, 2003. 

Hara, A. and H. Hirai. Comparative studies on immunochemical properties of female-specific serum protein and egg yolk proteins in rainbow trout (Salmo gairdneri). Comp. Biochem. Physiol. 59B 339—343, 1978. 

Hiramatsu, N. and A. Hara. Relationship between vitellogenin and its related egg yolk proteins in Sakhalin taimen (Hucho perryi). Comp. Biochem. Physiol. 115A 243 -251, 1996. 

Thorsen, A. and H.J. Fyhn. Final oocyte maturation in vivo and in vitro in marine fishes with pelagic eggs yolk protein hydrolysis and free amino acid content. J. Fish. Biol. 48 1195-1209, 1996. 

The preferential adsorption of caseinates over whey proteins was demonstrated by Britten and Giroux (1991b) and Hunt and Dalgleish (1994). a-la and P-lg showed similar affinity for adsorption at an interface (Dalgleish et al 1991). Dalgleish et al. (1991) also compared surface concentration of ovalbumin with that of P-lg and reported that p-lg had a much greater affinity for the interface. The egg yolk protein phosvitin also exhibited lower affinity for the interface compared with P-casein and p-lg (Dickinson et al., 1991). 

Table 6.9. Egg-yolk proteins from domestic fowl and their origin...

Steroid hormone regulation of the biosyndiesis of egg-yolk protein... 

Hormonal control of egg-yolk protein synthesis has been most extensively studied with vitellogenin and VLDL (Burley Vadehra, 1989). Unlike egg-white protein synthesis, there is only a primary response, and this does not require cell proliferation or DNA synthesis (Deeley et al., 1992). The livetins differ from the other major yolk proteins in that their synthesis is not under hormonal control (Burley, Evans Pearson, 1993). Both a- and ) -livetins are synthesised in the liver. They correspond in size and amino acid composition to serum albumin and all globulin, respectively, which are probably their precursors. Similarly y-livetin resembles y-globulin and it is synthesised in the bone marrow. 

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