Published work on the chemical composition of eggs, with particular reference to the protein and lipid constituents, is reviewed and summarised.

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Flow curves determined with a rotational Viscometer have shown that unfrozen raw and pasteurized liquid whole egg are Newtonian fluids and that thawed frozen whole egg is pseudo-plastic. For the latter a useful value for comparative purposes may be obtained by calculating the apparent viscosity at a selected low rate of shear. Some preliminary results illustrate the very large difference in viscosity between unfrozen egg and thawed frozen egg.

The proteins of whole egg may be separated into soluble and insoluble portions by dialysis against glycine solution followed by centrifugation at a high speed. The soluble proteins can then be resolved into at least twelve fractions by ion-exchange chromatography on diethylaminoethyl-cellulose, using stepwise elution with dilute glycine-phosphate buffer solutions containing increasing concentrations of sodium chloride. Further examination has shown that most of the fractions contain more than one protein, and some tentative identifications have been made. The insoluble proteins can be dissolved in a relatively strong phosphate buffer and fractionated on diethylaminoethyl-cellulose in a similar way. Separate examinations of white and yolk indicated that the soluble proteins of whole egg are predominantly the same as those of the white, and also showed certain differences between whole egg and the separated white and yolk that could be attributed to some form of protein association in mixed whole egg. An initial experiment has suggested that the method described will reveal differences between raw and pasteurised egg.

Zone electrophoresis assisted in the identification of several of the fractions isolated from white, yolk and whole egg, and particularly in following the distribution of the ovalbumin homologues. Certain artifacts in electropherograms of ovalbumin fractions were attributed to aggregation of this substance during freeze-drying. The ovalbumin in whole egg appears to have a slightly higher affinity for diethylaminoethylcellulose than when it is present in egg white only. Characteristics of some unidentified proteins are noted. The implications of all the findings are discussed and the susceptibility of the low density fraction of egg yolk to environmental change is emphasised.