STUDY OF THE PHENOMENON OF AGGLOMERATION IN THE YEAST SACCHAROMYCES CEREVISIAE

Abstract

Agglomeration or “grittiness” is detrimental to bakers' yeast quality. Gritty yeast only partially resuspends when mixed in water, most of it remaining as macroscopic cell aggregates. A macroscopic sedimentation test was developed for measuring agglomeration intensity. Expression of the gritty phenotype was investigated in two strains (N176 and GB1) of Saccharomyces cerevisiae grown on a 14‐liter scale by varying fermentation conditions of agitation and aeration. Results show that yeast agglomeration is different from yeast flocculation, and is determined by both strain genetic background and environmental factors. The gritty phenotype was expressed in the strain prone to agglomeration (N176) when dissolved oxygen was limiting in the fermenter. Gritty cells had a lower phosphorus and lipid concentration and a higher protein concentration at the surface of the cell, and a higher amount of whole cell and cell wall proteins and calcium than non‐gritty cells. Some proteins were also extracted from gritty cells with sodium hydroxide or mercaptoethanol, that were not present in non‐gritty cells. Agglomeration did not result in major differences in the structure or composition of the structural cell wall mannoprotein (CWMP). A model for agglomeration is proposed: proteins (cognors) activated by Ca2+ (cofactors) to increase their binding capacity bind the mannans (cognons) of adjoining cells; binding is facilitated by the lower phosphorus and lipid concentration at the surface of gritty cells. 1993 The Institute of Brewing & Distilling