Flocculation of cell walls of brewer's yeast and effects of metal ions, protein-denaturants and enzyme treatments

Abstract

Effects of metal ions, protein-denaturants and enzyme treatments on flocculation of cell walls of Beer Yeast IFO 2018 were investigated. Cell walls from flocculent cells grown in a complete medium were able to form flocs as were whole cells, but cell walls from non-flocculent cells, such as “Mg2+-deficient” cells, “early-phase” cells and “low-pH” cells, were not. The cell walls dispersed in distilled water reflocculated in solutions containing Ca2+ or other metal ions. Of the alkali metal ions tested, only Na+ inhibited flocculation of flocculent cell walls at a concentration more than 0.1 M. Ca2+ or Sn4+ was absolutely required for flocculation of cell walls in the physiological saline (NaCl, 150 mM), but the effect of Sn4+ seems rather non-specific, because it promoted flocculation of non-flocculent cell walls as well. Sr2+ and Ba2+ were antagonistic to Ca2+ and inhibited flocculation. Flocculation of cell walls was also depressed by high concentrations of protein-denaturants, e.g. urea and guanidine·HCl. Treatment with proteolytic enzymes deprived cell walls of floc-forming ability. Effect of metal ions, protein-denaturants and treatment with enzymes on the flocculation of intact cells was investigated as control. Since flocculating properties of cell walls were very similar to those of intact cells, flocculation must be an inherent property of cell walls.