Question from The Times of India

"Is it harmful to have the yolk of egg? If I mix one yolk with the whites of five eggs in my breakfast omelets, would that be okay or am I still asking for cholesterol problems?"

- Rushad Bana

"No, consuming the yolk is not totally harmful, especially if not eaten daily. Yes, the yolk contains most of the fat (99 per cent) of the egg, but it also contains a chunk of the nutrients, including 90 per cent of the calcium, iron, Vitamin B6 + B12, zinc, and folate content. Majority of the protein (100 per cent complete in all essential amino acids) content is in the egg white, and since it has just 1 per cent of the fat; it contributes very little calories to the daily intake. Thus egg whites can be had in multiple numbers daily."

Found here..
http://articles.timesofindia.indiatimes.com/2011-08-23/diet/29773720_1_jaggery-refined-white-sugar-egg-yolk/2

DEFINITION: Avidin

"Avidin is a tetrameric biotin-binding protein produced in the oviducts of birds, reptiles and amphibians deposited in the whites of their eggs. In chicken egg white, avidin makes up approximately 0.05% of total protein (approximately 1.8 mg per egg). The tetrameric protein contains four identical subunits (homotetramer), each of which can bind to biotin (Vitamin B7, vitamin H) with a high degree of affinity and specificity. The dissociation constant of avidin is measured to be KD ≈ 10−15 M, making it one of the strongest known non-covalent bonds.

"In its tetrameric form, avidin is estimated to be between 66–69 kDa in size. Ten percent of the molecular weight is attributed to carbohydrate content composed of four to five mannose and three N-acetylglucosamine residues. The carbohydrate moieties of avidin contain at least three unique oligosaccharide structural types that are similar in structure and composition.

"Functional avidin is found only in raw egg, as the biotin avidity of the protein is destroyed by cooking. The natural function of avidin in eggs is not known, although it has been postulated to be made in the ovaduct as a bacterial growth-inhibitor, by binding biotin the bacteria need. As evidence for this, streptavidin, a loosely related protein with equal biotin affinity and a very similar binding site, is made by certain strains of Streptomyces bacteria, and is thought to serve to inhibit the growth of competing bacteria, in the manner of an antibiotic.

"A non-glycosylated form of avidin has been isolated from commercially prepared product; however, it is not conclusive as to whether the non-glycosylated form occurs naturally or is a product of the manufacturing process."

http://en.wikipedia.org/wiki/Avidin

Avidin, which is found in raw egg whites, blocks the uptake of Vitamin B6 (Biotin) causing a vitamin deficiency. You must cook the egg white to neutralize the Avidin and allow your body to safely digest the protein and utilize all its Amino acids. Unfortunately, cooking also starts to destroy the protein.

http://www.eggwhitesint.com/healthfacts.htm

Egg Yolk

The yolk makes up about 33% of the liquid weight of the egg; it contains approximately 60 calories, three times the caloric content of the egg white.

The yolk of one large egg (50 g total, 17 g yolk) contains approximately: 2.7 g protein, 210 mg cholesterol, 0.61 g carbohydrates, and 4.51 g total fat. (USDA National Nutrient Database)

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 is typically as follows:[1]

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.

The yellow color is due to lutein and zeaxanthin, which are yellow or orange carotenoids known as xanthophylls.