Nutritive Component of Egg

By: Suharyanto

Egg Structure and Composition

• Shell +10%
• Albumen + 60%
• Yolk + 30%
• Ratio of shell, albumen, yolk :
- Hen egg = 12,3% : 55,8% : 31,9%
- Duck egg = 12% : 52,6% : 35,4%


Nutrition Content

component % Water Protein Fat CHO
All 100 74.6 12.1 11.2 1.2
Albumen 58 88.0 10.1 0.2 0.8
Yolk 31 48.0 16.4 32.9 2.0


Physically, albumen consist of 4 layers:
• Outer layer 23,2%, mucin fiber
• Midle layer (albuminous sac) 57,3%, myelinous mucin
• Inner layer 16,9%, highly thick of fluids, rare mucin.
• Membrana kalazifera layer 2,7%, myelinous mucin sparating yolk and albumin. It functions as a hold of yolk.


Protein in Albumen:
• Ovalbumin
– Monomeric phosphoglycoprotein
– 54% in albumen
• Ovotransferrin
• Ovomucoid
• Lysozyme
• Ovomucin
• Globulin


Ovalbumen:
• 54%, the greatest
• It can be readily purified and crystallized
• It is a monomeric phosphoglycoprotein
• It has a molecular weight of 45,000
• It has pI of 4.7.
• Function:
– foaming and gelling;
– structure of baked products.


Ovotransferin:
• 12%, second largest
• Or Conalbumen
• It is a monomeric glycoprotein
• Function: binds metal/ion and discolorization.
• Denaturate at 60oC


Ovomucoid:
• 11%
• Contains 20-25% carbohydrates
• These carbohydrates contribute to ovomucoid stability againts tryptic hydrolysis
• Function: protease inhibitor, mainly tripsin.
• Physically is stable, but biologic activity is lost severe heat treatment, 100oC for 60 min.

Ovomucin:
• A Fibrous Protein.
• Characterized by a highly viscous gel-like nature.
• Not soluble in water, soluble in a salt dilution at pH 9 or above.
• Contains 30% carbohydrates.
• 2 types present in egg white:
– Insoluble, from gel fraction (whole thick white).
– Soluble, from liquid fraction (thin fraction).
• contributes to the thickness of the white (4 x more abundant than in yolk).
• Plays role in the foaminess of egg white.
• contributes to the stability of egg white foam.


Lyzozime:
• 8%.
Lysozyme: ability to hydrolyze a polysaccharide in the cell wall of some bacteria to prevent bacterial spoilage
others: ovoinhibitor, ovoflavoprotein, ovomicroglobulin, avidin (binds biotin, but is heat sensitive)


Yolk
• Proteins (16.4%):
 plasma (78%): livetins & LDL (protein content ~ 10%)
 granular fraction: phosvitin (16%, carrier of Fe), lipovitellins (70%) & LDL (12%)
• Water (48%)
• Lipids (32 to 34%)
 triglycerol (66%)
 phospholipid (28%) including lecithin
 (has remarkable emulsifying ability)
 cholesterol (3%, or 250 mg)
• The color of yolk depends on the presence of carotenoids.
 xanthophylls not carotene
 (Lutein and zeaxanthin)

Posted in: Animal Product Technology