Composition and Functional Properties of Mottled Yolks

Abstract

Yolk mottling was induced by feeding 0.02% Nicarbazin to 6-month old White Leghorn pullets. A second group of pullets, fed a standard layer ration, served as the control. Eggs were collected for three months on a daily basis, but the yolks were pooled on a weekly basis for analysis. Composition and functional properties of both mottled and normal yolks were determined.The percent solids of normal yolks was significantly higher than mottled yolks. The pH of normal yolks was lower than mottled yolks but not significantly. Normal yolks contained higher percentage fat, protein, and ash than mottled yolks; however, the percent carbohydrate was lower in normal yolks. There was no difference in the cholesterol content of mottled and normal yolks. Normal yolks contained significantly higher percent calcium, phosphorus, and iron than mottled yolks.Emulsifying capacity and viscosity of normal yolks were greater than for mottled yolks. Foam volume and sponge cake volume were always larger for mottled yolks than for normal yolks, but normal yolks produced more stable foam and better cake texture.Electrophoretic separation of the components of mottled and normal yolks indicated that two egg white proteins were present in mottled yolks but not apparent in normal yolks. The two proteins are believed to be ovalbumin and conalbumin.