Application of aqueous two-phase partition in PEG-phosphate systems. Design and implementation of a prototype process for recovery of bulk protein fractions from waste brewer's yeast.

The practical development of a process exploiting aqueous two-phase partition in PEG/phosphate systems is described for the recovery and partial purification of a bulk protein fraction from waste Brewer's yeast. Inadequacies in current assumptions concerning de novo process design of such systems necessitated the empirical establishment of conditions for the two-step extraction of protein from wet-milled yeast suspensions. Experiments with homogeneous proteins and yeast extracts are presented to illustrate the true influence of phase volume upon primary protein extraction, and of added salts and modified system pH upon selective back extraction. A mechanistic description of physical and chemical factors influential upon selective phase partition in PEG/phosphate systems is discussed.