LPT 321: Meat Science (1+1)

PROTEINS, VITAMINS, AND PIGMENTS OF EGGS

Proteins

• Egg is a rich source of protein and the protein is of high quality.
• Proteins are present both in albumen and yolk.
• The predominant protein of albumen is ovalbumen which constitutes 54% of the total albumen protein.
• The other proteins present in albumen are conalbumin, ovomucoid, ovomucin, lysozyme, G₂ globulin, G₃ globulin, flavoprotein, avidin, ovomacroglobulin, ovoglycoprotein etc.
• The major protein in yolk is ovovitelline which constitutes 75% of the total yolk protein and the remaining 25% is constituted by ovolivetin.
• Ovovitelline is rich in phosphorus and one-third of phosphorus content of yolk is present in this fraction.
• Ovolivetin is rich in sulphur and contains nearly one-third of the total sulphur of yolk and a very small proportion of phosphorus.
• Proteins of vitelline and shell membranes are ovokeratin and ovomucin.
• Shell proteins are mainly collagen in nature.
• The proteins of egg contain all essential amino acids in correct proportions.

Vitamins

• Egg contains both water and fat soluble vitamins.

Enzymes

• Egg albumen contains the enzyme lysozyme, which is antimicrobial in nature and the yolk contains small amounts of catalase, peptidase, tributyrase, amylase, phosphatidase etc.

Pigments

• Shell pigments of egg include ovoporphyrin, which is responsible for the brownish tint of some eggs.
• Ovocyan gives bluish tint to eggs ( in Araucana breed of chicken).
• Some poultry egg shell membrane has a pinkish pigment porophyrin.
• Albumen pigment is ovoflavin which has a creamy tinge.
• Yolk pigments are of two types – water soluble pigment or lyochromes that resemble ovoflavin of albumen and fat soluble pigments or lipochromes which include carotenoids and xanthophylls.
• Carotenoids include ά and βcarotenes which have vitamin A activity.
• Xanthophylls include cryptoxanthene, zeaxanthene and lutein which have pigmenting property alone.