Cell surface properties and flocculation behaviour of industrial strains of Saccharomyces cerevisiae

Cellular adhesion properties of yeasts depend on the characteristics of the outer layer of the cell wall. In this study, the flocculation behaviour of four industrial strains of Saccharomyces cerevisiae used for production of beer, champagne, wine and fuel alcohol was evaluated; their flocculation abilities being, 42.5, 14.8, 13.8 and 11.6%, respectively. The brewing yeast strain was found to be the most flocculent. Very little flocculation was observed during the lag and logarithmic phases of growth (1-15%), while during the early and late stationary phases, different strains exhibited variable flocculation patterns. Cell surface hydrophobicity [assayed using hydrophobicity microsphere assay (HMA) and microbial adhesion to solvent (MATS) techniques] and surface charge (assayed by Alcian blue dye retention) played important roles in dictating flocculation behaviour in different yeast strains, as did the yeast growth phase. Percentage hydrophobicity index (HI) and percentage hydrophobicity of the four strains followed, respectively the same order, viz: Beer (66.6, 21.5) > Champagne (33, 10.5) > fuel alcohol (22.4, 7.4) > wine (20.5, 2.7). Our findings provide new insight into yeast cell surface properties and how these relate to behavioural characteristics of yeasts employed in industrial fermentations.