INFLUENCE OF SOME SELECTED IONS ON SYSTEM WATER ACTIVITY AND ON ETHANOL VAPOR-PRESSURE AND ITS INHIBITORY-ACTION ON SACCHAROMYCES-CEREVISIAE

The individual and interactive effects of some ionic species on the et hanol vapour pressure in equilibrium with the system, the water activi ty, and the fermentative performance of Saccharomyces cerevisiae were investigated. The concentrations of the ions Ca2+, Mg2+, and NH4+ were modulated according to a central composite design, within a range of values that can be individually considered optimal for S. cerevisiae. Although the temperature and ethanol and glucose concentrations were k ept constant, the initial water activity and ethanol vapour pressure o f the systems were remarkably affected by the interactions between the three ions studied. The data concerning the fermentative activity emp hasize the role of the physical state of ethanol. In fact, when the et hanol concentration was kept constant, the highest fermentative perfor mances of yeast were obtained when the ethanol vapour pressure, depend ing particularly on the Ca2+ and Mg2+ interaction, was the lowest in t he matrix of values considered.