Yolks

Phosphoproieins. Contain phosphates and include casein from milk and phosvilin from egg yolk. 

One of the xanthophyll pigments present in various leaves, seeds and fruits, and in yolk of egg. It is often present in company with lutein, of which it is an isomer. It bears the same relation to -carotene as lutein does to a-caro tene. 

Phosphorus, like nitrogen, is an essential constituent of living matter where it may be partly in combination (as phosphate groups) with organic groups, for example in lecithin and egg yolk, or mainly in inorganic form, as calcium phosphate(V), in bones and teeth. 

Lecithin. Lecithin [8002-43-5] (qv) is a mixture of fat-like compounds that includes phosphatidyl choline, phosphatidyl ethanolamines, inositol phosphatides, and other compounds (37). Commercial lecithin was originally obtained from egg yolks, but is now extracted from soybean oil. Lecithin is used in many products, including margarine, chocolate, ice cream, cake batter, and bread. 

To be classified as custard or French, product must contain >1.4% egg yolk solids. 

In 1936, biotin was isolated from egg yolks (8), in 1939 from beef Hver (9), and in 1942 from milk concentrates (10). Biotin-producing microorganisms exist in the large bowel but the extent and significance of this internal synthesis is unknown. 

Choline occurs widely in nature and, prepared synthetically, it is available as an article of commerce. Soybean lecithin and egg-yolk lecithin have been used as natural sources of choline for supplementing the diet. Other important natural-food sources include Hver and certain legumes (18—22). 

Physical Properties. The egg is composed of three basic parts shell, whites (albumen), and yolk. Each of these components has its own membranes to keep the component intact and separate from the other components. The vitelline membrane surrounds the yolk, which in turn is surrounded by the chala2iferous layer of albumen, keeping the yolk in place. Egg white (albumen) consists of an outer thin layer next to the shell, an outer thick layer near the shell, an inner thin layer, and finally, an inner thick layer next to the yolk. Thick layers of albumen have a higher level of ovomucin in addition to natural proportions of all the other egg white proteins. This ovomucin breaks into shorter fibers when the egg white is blended on a high speed mixer (3), or when the egg white ages. Viscosity is gready reduced when the egg white is blended in this way. 

Table 1 shows the various physical properties for components of eggs (4). Specific gravity of whites, yolks, and whole egg is the same, ie, density is 1035 kg/m (64.6 Ib/ft = 8.63 Ib/gal) for all three types of egg products shown. The viscosity of blended Hquid egg components varies over a wide range of temperatures at temperatures higher than those indicated in Table 1, the protein starts to denature and coagulate, increasing viscosity. 

The yolk is separated from the white by the vitelline membrane, and is made up of layers that can be seen upon careful examination. Egg yolk is a complex mixture of water, Hpids, and proteias. Lipid components iaclude glycerides, 66.2% phosphoUpids, 29.6% and cholesterol [57-88-5] 4.2%. The phosphohpids consist of 73% lecithin [8002 3-5] 15% cephahn [3681-36-7], and 12% other phosphohpids. Of the fatty acids, 33% are saturated and 67% unsaturated, including 42% oleic acid [112-80-1] and 7% linoleic acid [60-33-3]. Fatty acids can be changed by modifying fatty acids ia the laying feed (see... 

Nutrient SheU, whole Whole Liquid / fro2en White Yolk... 

Per 100 g based on 24.5% and 12.1% soHds, respectively, for whole and white Hquid. Yolk contains 44% egg soHds, diluted with egg white only. Proteia based oa total aitrogea multipHed by 6.25. 

Yolk comes from breaking machines at 45% or greater, and this is standardized to 43.5% soHds by adding mix and whites to the Hquid. USDA standards do not allow going below 43.0% soHds for yolk. SoHds to which product is standardized depends on customer specifications. 

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