Effect of pH on the ζ-potential and turbidity of yeast suspensions

The present work considers how changes in the ζ-potential affect the flocculation of yeast suspensions over the pH range from 3 to 10 using sodium chloride and aluminium sulphate as background electrolytes. The degree of flocculation is assessed both in terms of turbidity of the yeast suspensions and in changes to the size distributions of these suspensions. The results indicate that the ζ-potential of yeast depends on pH being positive below pH 3.5 and negative at higher pH. It is seen that when the ζ-potential is low, turbidity is low and the average particle size of flocs in suspension increases and when the ζ-potential is relatively higher the opposite is seen. It is found that the classical DLVO theory does not fully explain the observed changes in turbidity, however, when an additional repulsive force attributed to hydration energy is considered the extended DLVO provides a reasonable explanation of the experimental data.