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 b aking, brewing and distilling industries, which rely on yeast catabolism of mixtures of hexoses and maltose. Maltose utilisation requires the presence of maltose permease and cu-glucosidase (maltase), encoded by MAL genes. Sy nthesis 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 m altose metabolism. The extent of the lag was linked to the levels of maltos e 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 s ugar medium, enhanced sugar fermentation. Maltose pulsing of yeasts could t herefore be useful for enhancing some fermentations relevant to baking and other yeast industries.