EFFECT OF MUST TURBIDITY ON CELL-WALL POROSITY AND MACROMOLECULE EXCRETION OF SACCHAROMYCES-CEREVISIAE CULTIVATED ON GRAPE JUICE

Mannoproteins have a great technological importance such as improvemen t of proteic and tartaric acid stability or the stimulation of lactic acid bacteria, but their production in wine is still poorly understood . The influence of grape juice turbidity on Saccharomyces cerevisiae c ell wall characteristics was studied. Grape juice insoluble particles and colloids were shown to have no influence on yeast cell wall porosi ty during the lag time but their absence led to increased yeast cell w all porosity at the end of growth phase. Cell wall porosity increased during cell growth and decreased at the transition from the growing ph ase to the stationary phase. Leakage of cell wall components was linke d with cell wall porosity and composition. Such components were freed during growth and during the stationary phase entrance but not during the stationary phase. Compared with a non-clarified medium (380 NTU), a clarified medium (34 NTU) caused the cell wall composition to exhibi t a higher proteic content and a lower mannose content. These results suggest that the removal of grape juice particles and colloids has an action on the cell wall synthesis of proliferating yeast i.e. by lower ing the glycosylation of mannoproteins. This finding is in agreement w ith the high cell wall porosity observed and the macromolecule excreti on.