Role of the maltose in the simultaneous-saccharification-fermentation process from raw wheat starch and Saccharomyces cerevisiae

During the simultaneous-saccharification-fermentation from raw wheat starch, amyloglucosidase and commercial yeast, Saccharomyces cerevisiae, the fermentescible sugars profile, at the beginning of the process, plays a great role in the process regulation. From a liquefied wort, fermentescible sugars were glucose, maltose and maltotriose at concentration of 2 g/l, 40 g/l and 7 g/l, respectively. A complete hydrolysis of starch leads to a potential glucose concentration of 150 g/l. The general mechanism of a simultaneous-saccharification-fermentation occurs into two steps: the production of fermentescible sugars and the consumption of these by the yeast. In our case, maltose, dominating sugar in the wort, is the most significant sugar in the process regulation because it was substrate not only for the amyloglucosidase but also for the yeast. The maltose consumption by the yeast is repressed by the glucose, itself produced by the saccharification. We demonstrated that the apparent drop of maltose concentration in the wort acts as an activator of the amyloglucosidase and this fact allows a rapid ethanol production. The process is regulated by different interactions between glucose, maltose and maltotriose, the three sugars that, on one hand, are produced by the enzyme and on the other hand are used by the yeast.