Efficient ethanol production from wheat bran by enzymatic saccharification using commercially available enzyme products and fermentation using bakers' yeast

We aimed to produce ethanol efficiently by enzymatic saccharification coupled with ethanol fermentation using wheat bran as a biomass. For this purpose, we examined pretreatment conditions of biomass and a combination of commercially available enzyme products for saccharification. When a 3.3% (w/v) wheat bran suspension was pretreated using subcritical water at 140°C with a holding time of 0 h, followed by saccharification at 45°C using a mixture of commercially available Meiselase (composed of cellulase, ce!lobiase/β?- glucosidase, and xylanase) and Novozyme*188 (composed of cellobiase/βS-glucosidase,« amylase, and glucoamylase) at a ratio of 4 to 1 by weight, glucose was released at 10.6 g/l, which corresponded to 90% of the value calculated on the basis of the total amount of glucose-based saccharides contained in the wheat bran. On the other hand, from a pretreated 33% (w/v) wheat bran suspension, 85 g/l glucose was produced, which corresponded to only 72% of the theoretical value, owing to the inhibitory effect of glucose on β?-glucosidase activity. However, when fermentation was carried out at 30°C following 24-h saccharification of the pretreated wheat bran using a mixture of Meiselase and Novozyme*188, the inhibitory effect of glucose was considered to be reduced and as a result, after 21-h fermentation, ethanol was produced at 5.2% (w/v), which corresponded to 88% of the theoretical maximum value.