Simultaneous saccharification and fermentation of wheat bran to ethanol using a defined recombinant cellulase cocktail and industrial amylolytic Saccharomyces cerevisiae strains

Wheat bran, generated from the milling of wheat, represents a promising feedstock for the production of bioethanol. This substrate consists of three main components: starch, hemicellulose and cellulose. This study determined the optimal conditions for wheat bran hydrolysis using a recombinant cellulase cocktail (RCC), which contains two cellobiohydrolases, an endoglucanase and \u3b2-glucosidase. The 10% (w/v, expressed in terms of dry matter) substrate loading yielded the most glucose, while the 2% substrate loading gave the best hydrolysis efficiency (degree of saccharification), using unmilled wheat bran. The ethanol production of two industrial amylolytic Saccharomyces cerevisiae strains, MEL2[TLG1-SFA1] and M2n[TLG1-SFA1], were compared in an Simultaneous Saccharification and Fermentation (SSF) for 10% substrate loading and the optimised RCC. The recombinant yeast S. cerevisiae MEL2[TLG1-SFA1] and M2n[TLG1-SFA1] completely hydrolysed wheat bran starch producing similar amounts of ethanol (5.3 and 5.0 g l-1, respectively). Supplementing SSF with RCC resulted in additional ethanol production of about 2.0 g l-1. SEM analysis confirmed the effectiveness of both RCC and engineered amylolytic strains in terms of cellulose and starch depolymerisation. This study demonstrated that untreated wheat bran could be a promising ready-to-use substrate for ethanol production. The addition of crude recombinant cellulases improved ethanol yields in the SSF process and S. cerevisiae MEL2[TLG1-SFA1] and M2n[TLG1-SFA1] strains can efficiently convert starch to ethanol directly from starchy by-products