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

Abstract

During the simultaneous-sacchari®cation-fermentation from raw wheat starch, amyloglucosidase and commercial yeast, Saccharomyces cerevisiae, the fermentescible sugars pro®le, at the beginning of the process, plays a great role in the process regulation. From a lique®ed 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-sacchari®cation-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 signi®cant 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 sacchari®cation. 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.

Interlinked population balance and cybernetic models for the simultaneous saccharification and fermentation of natural polymers

“…In the context of polymeric fermentation, one example is the alcoholic fermentation of starch hydrolysates (i.e., the small sugars such as glucose, maltose, maltotriose etc.) by yeast where the presence of glucose generally represses the consumption of larger sugars (Duval et al, ; Ernandes et al, ; Montesinos and Navarro, ). In general, the use of the conventional unstructured models for microbial growth kinetics (Anuradha et al, ; Hofvendahl et al, ; Jang and Chou, ; Lee et al, ; Morales‐Rodriguez et al, ; Ochoa et al, ; Podkaminer et al, ) lacks the necessary robustness to handle complex nutrient environments (Ramkrishna and Song, ).…”

“…This strategy is only applicable when only two substrates are capable of being metabolized. For the breakdown of large polymers such as starch, clearly the microbes are incapable of consuming every reducing sugar in the broth but that only the smaller ones are consumed, e.g., glucose, maltose, and maltotriose for the yeast Saccharomyces cerevisiae (Duval et al, ; Ernandes et al, ; Montesinos and Navarro, ). As such, if the microbes are capable of metabolizing more than two substrates resulting from the breakdown of polymers, the choice of the key enzymes used to mimic the excretion of extracellular depolymerase is not apparent.…”