yolk

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yolk

1. the substance in an animal ovum consisting of protein and fat that nourishes the developing embryo
2. a greasy substance secreted by the skin of a sheep and present in the fleece

Yolk

 

(deutoplasm), a nutritive substance that accumulates in the ovum of animals and man in the form of granules or membranes that sometimes merge into a solid yolk mass (in insects, bony fish, and birds).

Yolk has been discovered in the ova of all animals and man, but its quantity and distribution vary considerably. In ova with a small amount of yolk, the yolk particles are distributed evenly throughout the cytoplasm (isolecithal ova). In ova with a large amount of yolk, the yolk particles are concentrated either in the vegetative part of the ovum (telolecithal ova) or in the central part of the cytoplasm, around the nucleus (centrolecithal ova). The type of egg cleavage depends on the quantity and distribution of the yolk. Chemically there are three principal varieties of yolk: protein, fat, and carbohydrate. However, in most animals the yolk granules have a complex chemical composition and contain proteins, fats, carbohydrates, ribonucleic acid, pigments, and mineral substances. For example, in the mature hen’s egg, the yolk contains 23 percent neutral fat, 16 percent protein, 11 percent phospholipids, 1.5 percent cholesterol, and 3 percent minerals. Various organelles of the ovum participate in the synthesis and accumulation of the yolk: the Golgi apparatus, endoplasmic reticulum, and mitochondria. In many animals the protein component of the yolk is synthesized outside the ovary and enters the growing ovum by means of pinocytosis. In some invertebrate animals the yolk may also accumulate in special cells of the ovary—the yolk cells, on which the developing embryo is nourished.

T. B. AIZENSHTADT

yolk

[yōk]
(biochemistry)
Nutritive material stored in an ovum.
The yellow spherical mass of food material that makes up the central portion of the egg of a bird or reptile.
References in periodicals archive ?
Authorities stated that the lanes were reopened during mid-afternoon after workers turned the truck upright and cleared the slippery liquid egg yolk from the roadway.
Gently spoon a quarter of the dried fig paste along the centre of each of the pastry pieces, and brush one side with a little beaten egg yolk and milk.
The team now hopes to adopt the technique to help rare breeds by taking out the egg yolk.
David Spence of Western University, Canada, and his team surveyed more than 1200 patients and found that regular consumption of egg yolks is about two-thirds as bad as smoking when it comes to increased build-up of carotid plaque, a risk factor for stroke and heart attack.
Surveying more than 1200 patients, Spence found regular consumption of egg yolks is about two-thirds as bad as smoking when it comes to increased build-up of carotid plaque, a risk factor for stroke and heart attack.
Whisk the egg yolks with 80g sugar until it becomes pale and creamy and set to one side.
Q Is it a good idea to throw out the egg yolk when cooking omelets?
It is shown that feeding the omega-3 fatty acid-rich flax oil and omega-6 fatty acid-rich soybean oil is in higher omega-3 and omega-6 fatty acids values in egg yolks [14].
3) Once the milk and cream are hot, pour them into the egg yolks and stir.