FURTHER EVIDENCE FOR THE CROSS-BRIDGING HYPOTHESIS FOR FLOCCULATION OF BREWER'S YEAST

Abstract

Mannan-protein has been extracted from the walls of various yeast strains. The range of side-chains of the mannan varies from strain to strain but differences do not correlate with flocculence. There is no correlation between flocculence and the levels of acidic amino acids present in the walls. The capacity of cells to flocculate by cross-bridging is proportional to the phosphate groupings present in the outer layer of the mannan-protein. The level of phosphate in the outer layer is sufficient only in the case of flocculent strains to enable binding of bivalent cations between adjacent cells. Scanning electron microscopy failed to reveal surface features of the walls relevant to flocculation.