Yolk
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Among animals which produce
As stored food, yolks are often rich in
The yolk is not living cell material like protoplasm, but largely passive material, that is to say deutoplasm. The food material and associated control structures are supplied during oogenesis. Some of the material is stored more or less in the form in which the maternal body supplied it, partly as processed by dedicated non-germ tissues in the egg, while part of the biosynthetic processing into its final form happens in the oocyte itself.[1]
Apart from animals, other organisms, like
Chicken egg yolk
In avian eggs, the yolk usually is a hue of yellow in color. It is spherical and is suspended in the
The yolk mass, together with the ovum proper (after fertilization, the
After the fertilization, the
As
Uses
- The developing embryo inside the egg uses the yolk as sustenance.
- It is at times emulsifier, and is used in mayonnaise, custard, hollandaise sauce, crème brûlée, avgolemono and ovos moles.
- It is used in painting as a component of traditional egg-tempera.
- It is used in the production of egg yolk agar plate medium, useful in testing for the presence of Clostridium perfringens.
- Egg yolk contains an IgY). The antibody transfers from the laying hen to the egg yolk by passive immunityto protect both embryo and hatchling from microorganism invasion.
- Egg yolk can be used to make liqueurs such as Advocaat or eggnog.
- Egg yolk is used to extract egg oil which has various cosmetic, nutritional, and medicinal uses.
Composition of chicken egg yolk
Nutritional value per 100 g (3.5 oz) | |
---|---|
Energy | 1,325 kJ (317 kcal) |
3.59 g | |
26.54 g | |
15.86 g | |
Tryptophan | 0.177 g |
Threonine | 0.687 g |
Isoleucine | 0.866 g |
Leucine | 1.399 g |
Lysine | 1.217 g |
Methionine | 0.378 g |
Cystine | 0.264 g |
Phenylalanine | 0.681 g |
Tyrosine | 0.678 g |
Valine | 0.949 g |
Arginine | 1.099 g |
Histidine | 0.416 g |
Alanine | 0.836 g |
Aspartic acid | 1.550 g |
Glutamic acid | 0.595 g |
Glycine | 0.488 g |
Proline | 0.545 g |
Serine | 1.326 g |
Vitamins | Quantity %DV† |
Vitamin A equiv. | 42% 381 μg |
Thiamine (B1) | 15% 0.176 mg |
Riboflavin (B2) | 41% 0.528 mg |
Pantothenic acid (B5) | 60% 2.990 mg |
Folate (B9) | 37% 146 μg |
Choline | 149% 820.2 mg |
Vitamin D | 27% 218 IU |
Minerals | Quantity %DV† |
Calcium | 10% 129 mg |
Iron | 15% 2.73 mg |
Magnesium | 1% 5 mg |
Phosphorus | 31% 390 mg |
Potassium | 4% 109 mg |
Zinc | 21% 2.30 mg |
Other constituents | Quantity |
Water | 52.31 g |
Cholesterol | 1085 mg |
One large egg contains 17 grams of yolk. | |
†Percentages estimated using US recommendations for adults,[7] except for potassium, which is estimated based on expert recommendation from the National Academies.[8] |
The yolk makes up about 33% of the liquid weight of the egg; it contains about 60 kilocalories (250 kJ), three times the energy content of the egg white, mostly due to its fat content.[clarification needed]
All of the fat-soluble vitamins (A, D, E and K) are found in the egg yolk. Egg yolk is one of the few foods naturally containing vitamin D.
The composition (by weight) of the most prevalent fatty acids in egg yolk typically is:[9]
- Unsaturated fatty acids:
- Oleic acid, 47%
- Linoleic acid, 16%
- Palmitoleic acid, 5%
- Linolenic acid, 2%
- Saturated fatty acids:
- Palmitic acid, 23%
- Stearic acid, 4%
- Myristic acid, 1%
Egg yolk is a source of lecithin, as well as egg oil, for cosmetic and pharmaceutical applications. Based on weight, egg yolk contains about 9% lecithin.[10]
The yellow color is due to
Yolk proteins
The different yolk's proteins have distinct roles. Phosvitins are important in sequestering calcium, iron, and other cations for the developing embryo. Phosvitins are one of the most phosphorylated (10%) proteins in nature; the high concentration of phosphate groups provides efficient metal-binding sites in clusters.[11][12] Lipovitellins are involved in lipid and metal storage, and contain a heterogeneous mixture of about 16% (w/w) noncovalently bound lipid, most being phospholipid. Lipovitellin-1 contains two chains, LV1N and LV1C.[13][14]
Yolk vitamins and minerals
Yolks hold more than 90% of the calcium, iron, phosphorus, zinc, thiamine, vitamin B6, folate, vitamin B12, and pantothenic acid of the egg. In addition, yolks cover all of the fat-soluble vitamins: A, D, E, and K in the egg, as well as all of the essential fatty acids.
A single yolk from a large egg contains roughly 22 mg of calcium, 66 mg of phosphorus, 9.5 micrograms of selenium, and 19 mg of potassium, according to the USDA.[15]
Double-yolk eggs
Double-yolk eggs occur when ovulation occurs too rapidly, or when one yolk becomes joined with another yolk. These eggs may be the result of a young hen's reproductive cycle not yet being synchronized.[16]
Double-yolked eggs seldom lead to successful hatchlings without human intervention, as the chicks interfere with each other's hatching process and do not survive.[17]
Higher-order yolks are rare, though hens are known to occasionally lay even triple-yolk eggs.[18]
-
Comparison of an egg and an egg with a double-yolk (closed)
-
Comparison of an egg and an egg with a double-yolk (opened)
-
Double-yolk egg - Opened
Yolkless eggs
Eggs without yolks are known as "dwarf" or "wind" eggs,[19] or the archaic term "cock egg".[20] Such an egg is most often a pullet's first effort, produced before her laying mechanism is fully ready. Mature hens rarely lay a yolkless egg, but sometimes a piece of reproductive tissue breaks away and passes down the tube. Such a scrap of tissue may stimulate the egg-producing glands to react as though it were a yolk and wrap it in albumen, membranes, and a shell as it travels through the egg tube. This is usually what causes an egg to contain a small particle of grayish tissue instead of a yolk.
Since these eggs contain no yolk, and therefore cannot hatch, they were traditionally believed to have been laid by roosters.[21] This type of egg occurs in many varieties of fowl and has been found in chickens, both standard and bantams, guineas, and coturnix quail.
Yolk color
The color of an egg yolk is directly influenced by the makeup of the chicken feed.[22] Egg yolk color is generally more yellow when given a feed containing a large component of yellow, fat-soluble pigments, such as the carotenes in dark green plant material, for example alfalfa. Although much emphasis is put onto the color of the egg yolk, it does not reliably reflect the nutritional value of an egg. For example, some of the natural pigments that produce a rich yolk color are xanthophylls without much nutritional value, rather than the carotenoids that act as provitamin A in the body. Also, a diet rich in vitamin A itself, but without A-provitamins or xanthophylls, can produce practically colourless yolks that are just as nutritious as any richly colored yolks.
Yolks, particularly from free-range eggs, can be of a wide range of colors, ranging from nearly white, through yellow and orange, to practically red, or even olive green, depending on the pigments in their feed. Feeding fowl large amounts of capsicum peppers, for example, tends to result in red or deep orange yolks. This has nothing to do with adding colors such as cochineal to eggs in cooking.[23]
In fish
All
See also
References
- ISBN 978-0-632-04761-1.
- ^ Bellairs, Ruth; Osmond, Mark (2005). Atlas of Chick Development (2 ed.). Academic Press. pp. 1–4. link.
- ^ Bellairs, R., Harkness, M. & Harkness, R. D. (1963). The vitelline membrane of the hen's egg: a chemical and electron microscopical study. Journal of Ultrastructure Research, 8, 339–59.
- ^ Landecker, Hannah (2007). Culturing life: how cells became technologies. Cambridge, MA: Harvard University Press. p. 49. link.
- ^ Patten, B. M. (1951). Early Embryology of the Chick, 4th edition. McGraw-Hill, New York, p. 17.
- ^ Callebaut, M. (2008) Historical evolution of preformistic versus neoformistic (epigenetic) thinking in embryology, Belgian Journal of Zoology, vol. 138 (1), pp. 20–35, 2008
- ^ United States Food and Drug Administration (2024). "Daily Value on the Nutrition and Supplement Facts Labels". Retrieved 2024-03-28.
- )
- ISBN 0-309-02440-4; p. 203, online edition
- ISBN 978-0-85404-629-4. Retrieved 2013-03-20.
Egg yolk has the approximate composition (by weight) of 50% water, 16% protein, 9% lecithin, 23% other fat, 0.3% carbohydrate and 1.7% minerals.
- S2CID 7695406.
- S2CID 30240374.
- PMID 12135361.
- PMID 9687371.
- ^ U.S. Department of Agriculture, Agricultural Research Service, 2010. USDA National Nutrient Database for Standard Reference, Release 23, Nutrient Data Laboratory Home Page: http://www.ars.usda.gov/nutrientdata
- ^ "Odd Eggs, Double Yolks, No Yolks, etc". poultryhelp.com. 2005-03-04. Retrieved 2008-10-25.
- ^ Kruszelnicki, Karl S. (2003). "Double-yolked eggs and chicken development". Australian Broadcasting Corporation. Retrieved 2007-12-09.
- .
- S2CID 4280287.
- ^ "Cock's egg". Retrieved 2010-09-02.
- ^ "OEDILF – Word Lookup". www.oedilf.com.
- ^ Poultry Science by richard page 216 [full citation needed]
- ISBN 978-0-470-95911-4. Retrieved 1 September 2013.
- S2CID 46922423.
- ISBN 1-56465-193-2
- ISBN 92-5-104543-7. OCLC 156157504.
External links
- Anatomy of an Egg from the Exploratorium
- Making egg tempera from the Society of Tempera Painters