LIPIDS PRESENT IN EGGS 811 



(1) The Composition of Eggs 



The lipids in egg are concentrated in the yolk, and only a trace is found 

 in the white. The average composition of the egg is given in Table 27. 



Table 27 

 The Approximate Average Composition (in per Cent) of Hens' Eggs' 1 



Whole egg Yolk White 



Category A v. = 44 g. Av. = 16 g. A v. = 28 g. 



Water 73.0 49.0 85.0 



Lipid 12.0 33.0 Trace 



Protein 12.5 16.0 11.5 



Carbohydrate 0.5 0.5 0.6 



Ash 1.0 1.5 0.5 



a Adapted from E. S. West and W. R. Todd, Textbook of Biochemistry, Macmillan, 

 New York, 1951, p. 1215. 



One-third of the yolk of the hen's egg is lipid. It consists of about one- 

 third phospholipids and two-thirds cholesterol and neutral fat. The total 

 cholesterol content is 0.2 to 0.4 g. per egg, and the average phospholipid 

 is 2.0 g. per egg. 49 



a. Fatty Acids Present in Eggs. Riemenschneider et al. 58S reported the 

 presence of oleic, linoleic, and clupanodonic acids in egg-yolk lecithin and 

 glycerides, as well as small amounts of palmitoleic acid (9,10-hexadecenoic 

 acid). Palmitic and stearic acids were also present. According to Rie- 

 menschneider et al., m the average proportion of the saturated acids, by 

 weight, in the glycerides and phospholipids of egg yolk are as follows: 

 myristic, 0.7, not shown; palmitic, 25.2, 31.8; and stearic, 7.5, 4.1. In 

 the unsaturated group, the following average proportions, by weight, were 

 reported in the glyceride and phospholipid fractions, respectively: palmit- 

 oleic, 3.3, not shown; oleic, 52.4, 42.6; linoleic, 8.6, 8.2; clupanodonic, 

 2.3, 13.3; and total unsaturated acids, 66.6, 64.1. It appears that palmit- 

 oleic acid occurs only in the glycerides, while the highly unsaturated acid, 

 clupanodonic, is concentrated mainly in the lecithin (phospholipid) fraction. 



The mean figures for the iodine number of the egg lipids vary between 

 80 and 90. Mottram 589 reported that some variations existed between 

 different hens, but that the iodine number of the fat from any particular 

 fowl was extremely constant. It was likewise constant for hens of each 

 breed, respectively, and for eggs of birds in any certain locality. Incubation 



688 R. W. Riemenschneider, N. R. Ellis, and H. W. Titus, J. Biol. Chem., 126, 255-263 

 (1938). 



639 V. H. Mottram, J. Physiol, 47, xviii-xix (1913). 



