The mechanism of flocculation of a Saccharomyces cerevisiae cell homogenate using polyethyleneimine

The effects of polyethyleneimine, electrolyte concentration and pH on the electrophoretic mobility values for whole yeast, yeast homogenate and borax clarified homogenate were observed. The polyethyleneimine concentration at which there is optimum clarification of the borax-clarified homogenate corresponded to a mobility value of zero. Increased flee size up to the point of zero mobility was obtained by use of polyethyleneimine of larger molecular weight and also higher concentration. The effect of ageing under shear on the size of the flocs was examined and indicated reversibility of break-up at low shear rates while at higher shear rates the flocs were irreversibly broken. Such growth and ageing observations suggest flee formation comprises a two-stage process; the initial formation of primary particles by polymer bridging, and the subsequent formation of larger flocs as these primary particles are brought together by charge neutralisation.