Enhancement of maltose utilisation by Saccharomyces cerevisiae in medium containing fermentable hexoses.

Some industrial strains of Saccharomyces cerevisiae are unable to maintain high rates of fermentation during transition from catabolism of hexoses to maltose. This phenomenon, termed 'maltose lag', presents problems for the baking, brewing and distilling industries, which rely on yeast catabolism of mixtures of hexoses and maltose. Maltose utilisation requires the presence of maltose permease and alpha-glucosidase (maltase), encoded by MAL genes. Synthesis of these is induced by maltose and repressed by glucose. One strain of baker's yeast used in this work exhibited a marked maltose lag, whereas a second strain exhibited a shorter lag during conversion from hexose to maltose metabolism. The extent of the lag was linked to the levels of maltose permease and maltase in cells at the time of inoculation into mixed sugar medium. This view is supported by results showing that pulsing yeast with maltose to induce expression of MAL genes prior to inoculation into mixed sugar medium, enhanced sugar fermentation. Maltose pulsing of yeasts could therefore be useful for enhancing some fermentations relevant to baking and other yeast industries.