Preparation of Crystallized Egg Albumin (Ovalbumin)

Abstract

Sörensen 1 indicates that crystallized egg albumin, in contrast to most common proteins, may be considered to be a distinct chemical individual. Since this property makes it especially suitable for studies on the physico-chemical and immunological behavior of proteins, a simple, dependable method for its preparation is desirable.

In all the standard methods for the preparation of crystallized egg albumin, fresh egg white is first treated with an equal volume of saturated ammonium sulphate solution, to precipitate the so-called egg “globulin”. The filtrate from this sticky, dough-like precipitate of globulin is then ordinarily brought to the neighborhood of the iso-electric point of the ovalbumin, where crystallization takes place, by the addition of the required amounts of acetic, hydrochloric or sulphuric acids. Hektoen and Cole 2 pointed out that the voluminous precipitate of “globulin” obtained from egg white is not a true globulin, but a mixture or compound of all the proteins in egg white. When extracted with distilled water, the greater portion of it dissolves, leaving behind a clear, gelatinous residue which has the physical properties, at least, of a mucin. The water soluble portion yields crystals of ovalbumin, and contains large quantities of the non-crystallizable conalbumin as well as some ovomucoid.

In the present method, fresh egg white is beaten lightly to break up the membranes, strained through cheese cloth and then acidified by the gradual addition, with constant stirring, of one volume of N/1 acetic acid for each 9 volumes of egg white. Measurements made with the quinhydrone electrode on numerous samples of fresh egg white indicate that this amount of acid is sufficient to bring the material to a pH of 5.0 or less, where, as shown by Sörensen and Höyrup 3 crystallization of the ovalbumin readily takes place.